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Li Z, Yang M, Zhou C, Shi P, Hu P, Liang B, Jiang Q, Zhang L, Liu X, Lai C, Zhang T, Song H. Deciphering the molecular toolkit: regulatory elements governing shell biomineralization in marine molluscs. Integr Zool 2024. [PMID: 39030865 DOI: 10.1111/1749-4877.12876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/22/2024]
Abstract
The intricate process of shell biomineralization in marine molluscs is governed by a complex interplay of regulatory elements, encompassing secretomes, transporters, and noncoding RNA. This review delves into recent advancements in understanding these regulatory mechanisms, emphasizing their significance in elucidating the functions and evolutionary dynamics of the molluscan shell biomineralization process. Central to this intricate orchestration are secretomes with diverse functional domains, selectively exported to the extrapallial space, which directly regulate crystal growth and morphology. Transporters are crucial for substrate transportation in the calcification and maintenance of cellular homeostasis. Beyond proteins and transporters, noncoding RNA molecules are integral components influencing shell biomineralization. This review underscores the nonnegligible roles played by these genetic elements at the molecular level. To comprehend the complexity of biomineralization in mollusc, we explore the origin and evolutionary history of regulatory elements, primarily secretomes. While some elements have recently evolved, others are ancient genes that have been co-opted into the biomineralization toolkit. These elements undergo structural and functional evolution through rapidly evolving repetitive low-complexity domains and domain gain/loss/rearrangements, ultimately shaping a distinctive set of secretomes characterized by both conserved features and evolutionary innovations. This comprehensive review enhances our understanding of molluscan biomineralization at the molecular and genetic levels.
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Affiliation(s)
- Zhuoqing Li
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Meijie Yang
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Cong Zhou
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Pu Shi
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Pengpeng Hu
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Bin Liang
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Qingtian Jiang
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- Key Laboratory of Evolution & Marine Biodiversity (Ministry of Education) and Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, China
| | - Lili Zhang
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- Key Laboratory of Evolution & Marine Biodiversity (Ministry of Education) and Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, China
| | - Xiaoyan Liu
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- Qingdao Agricultural University, Qingdao, China
| | - Changping Lai
- Lianyungang Blue Carbon Marine Technology Co., Lianyungang, China
| | - Tao Zhang
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Hao Song
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
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Ayuyan AG, Cherny VV, Chaves G, Musset B, Cohen FS, DeCoursey TE. Interaction with stomatin directs human proton channels into cholesterol-dependent membrane domains. Biophys J 2024:S0006-3495(24)00168-1. [PMID: 38444158 DOI: 10.1016/j.bpj.2024.03.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Revised: 01/24/2024] [Accepted: 03/01/2024] [Indexed: 03/07/2024] Open
Abstract
Many membrane proteins are modulated by cholesterol. Here we report profound effects of cholesterol depletion and restoration on the human voltage-gated proton channel, hHV1, in excised patches but negligible effects in the whole-cell configuration. Despite the presence of a putative cholesterol-binding site, a CARC motif in hHV1, mutation of this motif did not affect cholesterol effects. The murine HV1 lacks a CARC sequence but displays similar cholesterol effects. These results argue against a direct effect of cholesterol on the HV1 protein. However, the data are fully explainable if HV1 preferentially associates with cholesterol-dependent lipid domains, or "rafts." The rafts would be expected to concentrate in the membrane/glass interface and to be depleted from the electrically accessible patch membrane. This idea is supported by evidence that HV1 channels can diffuse between seal and patch membranes when suction is applied. Simultaneous truncation of the large intracellular N and C termini of hHV1 greatly attenuated the cholesterol effect, but C truncation alone did not; this suggests that the N terminus is the region of attachment to lipid domains. Searching for abundant raft-associated proteins led to stomatin. Co-immunoprecipitation experiment results were consistent with hHV1 binding to stomatin. The stomatin-mediated association of HV1 with cholesterol-dependent lipid domains provides a mechanism for cells to direct HV1 to subcellular locations where it is needed, such as the phagosome in leukocytes.
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Affiliation(s)
- Artem G Ayuyan
- Department of Physiology & Biophysics, Rush University, Chicago, Illinois.
| | - Vladimir V Cherny
- Department of Physiology & Biophysics, Rush University, Chicago, Illinois
| | - Gustavo Chaves
- Institut für Physiologie, Pathophysiologie und Biophysik, CPPB, Paracelsus Medical University, Nürnberg, Germany
| | - Boris Musset
- Institut für Physiologie, Pathophysiologie und Biophysik, CPPB, Paracelsus Medical University, Nürnberg, Germany
| | - Fredric S Cohen
- Department of Physiology & Biophysics, Rush University, Chicago, Illinois
| | - Thomas E DeCoursey
- Department of Physiology & Biophysics, Rush University, Chicago, Illinois.
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3
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DeCoursey TE. Transcendent Aspects of Proton Channels. Annu Rev Physiol 2024; 86:357-377. [PMID: 37931166 PMCID: PMC10938948 DOI: 10.1146/annurev-physiol-042222-023242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2023]
Abstract
A handful of biological proton-selective ion channels exist. Some open at positive or negative membrane potentials, others open at low or high pH, and some are light activated. This review focuses on common features that result from the unique properties of protons. Proton conduction through water or proteins differs qualitatively from that of all other ions. Extraordinary proton selectivity is needed to ensure that protons permeate and other ions do not. Proton selectivity arises from a proton pathway comprising a hydrogen-bonded chain that typically includes at least one titratable amino acid side chain. The enormously diverse functions of proton channels in disparate regions of the phylogenetic tree can be summarized by considering the chemical and electrical consequences of proton flux across membranes. This review discusses examples of cells in which proton efflux serves to increase pHi, decrease pHo, control the membrane potential, generate action potentials, or compensate transmembrane movement of electrical charge.
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Affiliation(s)
- Thomas E DeCoursey
- Department of Physiology & Biophysics, Rush University, Chicago, Illinois, USA;
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4
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Fujiwara Y. Temperature Dependent Activity of the Voltage-Gated Proton Channel. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2024; 1461:109-125. [PMID: 39289277 DOI: 10.1007/978-981-97-4584-5_8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/19/2024]
Abstract
Voltage-gated proton channel (Hv) has activity of proton transport following electrochemical gradient of proton. Hv is expressed in neutrophils and macrophages of which functions are physiologically temperature-sensitive. Hv is also expressed in human sperm cells and regulates their locomotion. H+ transport through Hv is both regulated by membrane potential and pH difference across biological membrane. It is also reported that properties of Hv such as proton conductance and gating are highly temperature-dependent. Hv consists of the N-terminal cytoplasmic domain, the voltage sensor domain (VSD), and the C-terminal coiled-coil domain, and H+ permeates through VSD voltage-dependently. The functional unit of Hv is a dimer via the interaction between C-terminal coiled-coils assembly domain. We have reported that the coiled-coil domain of Hv has the nature of dissociation around our bodily temperature and mutational change of the coiled-coil affected temperature-sensitive gating, especially its temperature threshold. The temperature-sensitive gating is assessed from two separate points: temperature threshold and temperature dependence. In this chapter, I describe physiological roles and molecular structure mechanisms of Hv by mainly focusing on thermosensitive properties.
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Affiliation(s)
- Yuichiro Fujiwara
- Molecular Physiology & Biophysics, Faculty of Medicine/Graduate School of Medicine, Kagawa University, Miki-cho, Kagawa, Japan.
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5
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Wheeler GL, Sturm D, Langer G. Gephyrocapsa huxleyi (Emiliania huxleyi) as a model system for coccolithophore biology. JOURNAL OF PHYCOLOGY 2023; 59:1123-1129. [PMID: 37983837 DOI: 10.1111/jpy.13404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Accepted: 10/10/2023] [Indexed: 11/22/2023]
Abstract
Coccolithophores are the most abundant calcifying organisms in modern oceans and are important primary producers in many marine ecosystems. Their ability to generate a cellular covering of calcium carbonate plates (coccoliths) plays a major role in marine biogeochemistry and the global carbon cycle. Coccolithophores also play an important role in sulfur cycling through the production of the climate-active gas dimethyl sulfide. The primary model organism for coccolithophore research is Emiliania huxleyi, now named Gephyrocapsa huxleyi. G. huxleyi has a cosmopolitan distribution, occupying coastal and oceanic environments across the globe, and is the most abundant coccolithophore in modern oceans. Research in G. huxleyi has identified many aspects of coccolithophore biology, from cell biology to ecological interactions. In this perspective, we summarize the key advances made using G. huxleyi and examine the emerging tools for research in this model organism. We discuss the key steps that need to be taken by the research community to advance G. huxleyi as a model organism and the suitability of other species as models for specific aspects of coccolithophore biology.
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Affiliation(s)
- Glen L Wheeler
- The Marine Biological Association of the United Kingdom, The Laboratory, Plymouth, UK
| | - Daniela Sturm
- The Marine Biological Association of the United Kingdom, The Laboratory, Plymouth, UK
- School of Ocean and Earth Science, University of Southampton, Southampton, UK
| | - Gerald Langer
- Institute of Environmental Science and Technology (ICTA-UAB), Universitat Autònoma de Barcelona, Barcelona, Spain
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Zhao C, Webster PD, De Angeli A, Tombola F. Mechanically-primed voltage-gated proton channels from angiosperm plants. Nat Commun 2023; 14:7515. [PMID: 37980353 PMCID: PMC10657467 DOI: 10.1038/s41467-023-43280-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Accepted: 11/06/2023] [Indexed: 11/20/2023] Open
Abstract
Voltage-gated and mechanically-gated ion channels are distinct classes of membrane proteins that conduct ions across gated pores and are turned on by electrical or mechanical stimuli, respectively. Here, we describe an Hv channel (a.k.a voltage-dependent H+ channel) from the angiosperm plant A. thaliana that gates with a unique modality as it is turned on by an electrical stimulus only after exposure to a mechanical stimulus, a process that we call priming. The channel localizes in the vascular tissue and has homologs in vascular plants. We find that mechanical priming is not required for activation of non-angiosperm Hvs. Guided by AI-generated structural models of plant Hv homologs, we identify a set of residues playing a crucial role in mechanical priming. We propose that Hvs from angiosperm plants require priming because of a network of hydrophilic/charged residues that locks the channels in a silent resting conformation. Mechanical stimuli destabilize the network allowing the conduction pathway to turn on. In contrast to many other channels and receptors, Hv proteins are not thought to possess mechanisms such as inactivation or desensitization. Our findings demonstrate that angiosperm Hv channels are electrically silent until a mechanical stimulation turns on their voltage-dependent activity.
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Affiliation(s)
- Chang Zhao
- Department of Physiology and Biophysics, University of California, Irvine, CA, 92697, USA
| | - Parker D Webster
- Department of Physiology and Biophysics, University of California, Irvine, CA, 92697, USA
| | - Alexis De Angeli
- IPSiM, University of Montpellier, CNRS, INRAE, Institut Agro, Montpellier, France.
| | - Francesco Tombola
- Department of Physiology and Biophysics, University of California, Irvine, CA, 92697, USA.
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Wu F, Guo J, Duan H, Li T, Wang Y, Wang Y, Wang S, Feng Y. Ocean Acidification Affects the Response of the Coastal Coccolithophore Pleurochrysis carterae to Irradiance. BIOLOGY 2023; 12:1249. [PMID: 37759648 PMCID: PMC10525560 DOI: 10.3390/biology12091249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Accepted: 09/16/2023] [Indexed: 09/29/2023]
Abstract
The ecologically important marine phytoplankton group coccolithophores have a global distribution. The impacts of ocean acidification on the cosmopolitan species Emiliania huxleyi have received much attention and have been intensively studied. However, the species-specific responses of coccolithophores and how these responses will be regulated by other environmental drivers are still largely unknown. To examine the interactive effects of irradiance and ocean acidification on the physiology of the coastal coccolithophore species Pleurochrysis carterae, we carried out a semi-continuous incubation experiment under a range of irradiances (50, 200, 500, 800 μmol photons m-2 s-1) at two CO2 concentration conditions of 400 and 800 ppm. The results suggest that the saturation irradiance for the growth rate was higher at an elevated CO2 concentration. Ocean acidification weakened the particulate organic carbon (POC) production of Pleurochrysis carterae and the inhibition rate was decreased with increasing irradiance, indicating that ocean acidification may affect the tolerating capacity of photosynthesis to higher irradiance. Our results further provide new insight into the species-specific responses of coccolithophores to the projected ocean acidification under different irradiance scenarios in the changing marine environment.
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Affiliation(s)
- Fengxia Wu
- College of Marine and Environment, Tianjin University of Science and Technology, Tianjin 300453, China
- School of Oceanography, Shanghai Jiao Tong University, Shanghai 200040, China
| | - Jia Guo
- College of Marine and Environment, Tianjin University of Science and Technology, Tianjin 300453, China
| | - Haozhen Duan
- College of Marine and Environment, Tianjin University of Science and Technology, Tianjin 300453, China
| | - Tongtong Li
- College of Marine and Environment, Tianjin University of Science and Technology, Tianjin 300453, China
| | - Yanan Wang
- College of Marine and Environment, Tianjin University of Science and Technology, Tianjin 300453, China
| | - Yuntao Wang
- State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China
| | - Shiqiang Wang
- College of Marine and Environment, Tianjin University of Science and Technology, Tianjin 300453, China
| | - Yuanyuan Feng
- School of Oceanography, Shanghai Jiao Tong University, Shanghai 200040, China
- Shanghai Frontiers Science Center of Polar Science (SCOPS), Shanghai 200030, China
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8
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Chen C, Hu X, Gao Y, Liang J, Sun L. Ion fluxes Involved in the Adaptation of the Estuarine Diatom Coscinodiscus centralis Ehrenberg to Salinity Stress. Int J Mol Sci 2023; 24:13683. [PMID: 37761980 PMCID: PMC10531401 DOI: 10.3390/ijms241813683] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 08/17/2023] [Accepted: 08/18/2023] [Indexed: 09/29/2023] Open
Abstract
Although estuarine diatoms have a wide range of salt tolerance, they are often severely stressed by elevated salt concentrations. It remains poorly understood how estuarine diatoms maintain ionic homeostasis under high-salinity conditions. Using a scanning ion-selective electrode technique, this study determined the fluxes of H+, Na+, and K+ involved in the acclimatization of the estuarine diatom Coscinodiscus centralis Ehrenberg after an elevation in salinity from 15 psu to 35 psu. The C. centralis cells exhibited marked H+ effluxes after a transient treatment (TT, 30 min) and short-term treatment (ST, 24 h). However, a drastic shift of H+ efflux toward an influx was induced in the long-term treatment (LT, 10 days). The Na+ flux under TT, ST, and LT salinity conditions was found to accelerate the Na+ efflux. More pronounced effects were observed under the ST and LT salinity conditions compared to the TT salinity condition. The K+ influx showed a significant increase under the LT salinity condition. However, the salinity-induced Na+/H+ exchange in the estuarine diatom was inhibited by amiloride and sodium orthovanadate. These results indicate that the Na+ extrusion in salt-stressed cells is mainly the result of an active Na+/H+ antiport across the plasma membrane. The pattern of ion fluxes under the TT and ST salinity conditions were different from those under the LT salinity conditions, suggesting an incomplete regulation of the acclimation process in the estuarine diatom under short-term salinity stress.
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Affiliation(s)
- Changping Chen
- Key Laboratory of Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen 361102, China; (X.H.); (J.L.)
| | - Xiao Hu
- Key Laboratory of Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen 361102, China; (X.H.); (J.L.)
| | - Yahui Gao
- Key Laboratory of Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen 361102, China; (X.H.); (J.L.)
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, China;
| | - Junrong Liang
- Key Laboratory of Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen 361102, China; (X.H.); (J.L.)
| | - Lin Sun
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, China;
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9
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Dubicka Z, Bojanowski MJ, Bijma J, Bickmeyer U. Mg-rich amorphous to Mg-low crystalline CaCO 3 pathway in foraminifera. Heliyon 2023; 9:e18331. [PMID: 37519760 PMCID: PMC10375801 DOI: 10.1016/j.heliyon.2023.e18331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 07/13/2023] [Accepted: 07/13/2023] [Indexed: 08/01/2023] Open
Abstract
Calcium carbonate minerals produced by marine organisms play a central role in the global carbon cycle and carbonate sedimentation, which influence the climate by regulating atmospheric CO2 levels. Foraminifera are important marine single-celled organisms that have produced calcite shells for over 300 million years. Here, we present new observations promoting our understanding for foraminiferal biocalcification by studying Amphistegina lessonii. We integrated in vivo confocal autofluorescence and dye fluorescence imaging with elemental analysis of the cell supporting the concept that the calcite shells of foraminifera are produced via deposition of intracellularly formed Mg-rich amorphous calcium carbonate (Mg-ACC) particles that transform into a stable mineral phase. This process is likely accompanied by the activity of endosymbiotic microalgae and seawater-derived endocytic vesicles that provide calcification substrates such as DIC, Ca2+, and Mg2+. The final transformation of semi-liquid amorphous nanoparticles into a crystalline shell was associated with Mg2+ liberation.
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Affiliation(s)
- Zofia Dubicka
- Ecological Chemistry, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, 27-570, Germany
- University of Warsaw, Warsaw, 02-089, Poland
| | | | - Jelle Bijma
- Marine Biogeosciences, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, 27-570, Germany
| | - Ulf Bickmeyer
- Ecological Chemistry, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, 27-570, Germany
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10
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Chaves G, Jardin C, Derst C, Musset B. Voltage-Gated Proton Channels in the Tree of Life. Biomolecules 2023; 13:1035. [PMID: 37509071 PMCID: PMC10377628 DOI: 10.3390/biom13071035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2023] [Revised: 06/14/2023] [Accepted: 06/21/2023] [Indexed: 07/30/2023] Open
Abstract
With a single gene encoding HV1 channel, proton channel diversity is particularly low in mammals compared to other members of the superfamily of voltage-gated ion channels. Nonetheless, mammalian HV1 channels are expressed in many different tissues and cell types where they exert various functions. In the first part of this review, we regard novel aspects of the functional expression of HV1 channels in mammals by differentially comparing their involvement in (1) close conjunction with the NADPH oxidase complex responsible for the respiratory burst of phagocytes, and (2) in respiratory burst independent functions such as pH homeostasis or acid extrusion. In the second part, we dissect expression of HV channels within the eukaryotic tree of life, revealing the immense diversity of the channel in other phylae, such as mollusks or dinoflagellates, where several genes encoding HV channels can be found within a single species. In the last part, a comprehensive overview of the biophysical properties of a set of twenty different HV channels characterized electrophysiologically, from Mammalia to unicellular protists, is given.
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Affiliation(s)
- Gustavo Chaves
- Center of Physiology, Pathophysiology and Biophysics, The Nuremberg Location, Paracelsus Medical University, 90419 Nuremberg, Germany
| | - Christophe Jardin
- Center of Physiology, Pathophysiology and Biophysics, The Nuremberg Location, Paracelsus Medical University, 90419 Nuremberg, Germany
| | - Christian Derst
- Center of Physiology, Pathophysiology and Biophysics, The Nuremberg Location, Paracelsus Medical University, 90419 Nuremberg, Germany
| | - Boris Musset
- Center of Physiology, Pathophysiology and Biophysics, The Nuremberg Location, Paracelsus Medical University, 90419 Nuremberg, Germany
- Center of Physiology, Pathophysiology and Biophysics, The Salzburg Location, Paracelsus Medical University, 5020 Salzburg, Austria
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11
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Skeffington A, Fischer A, Sviben S, Brzezinka M, Górka M, Bertinetti L, Woehle C, Huettel B, Graf A, Scheffel A. A joint proteomic and genomic investigation provides insights into the mechanism of calcification in coccolithophores. Nat Commun 2023; 14:3749. [PMID: 37353496 PMCID: PMC10290126 DOI: 10.1038/s41467-023-39336-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Accepted: 06/05/2023] [Indexed: 06/25/2023] Open
Abstract
Coccolithophores are globally abundant, calcifying microalgae that have profound effects on marine biogeochemical cycles, the climate, and life in the oceans. They are characterized by a cell wall of CaCO3 scales called coccoliths, which may contribute to their ecological success. The intricate morphologies of coccoliths are of interest for biomimetic materials synthesis. Despite the global impact of coccolithophore calcification, we know little about the molecular machinery underpinning coccolithophore biology. Working on the model Emiliania huxleyi, a globally distributed bloom-former, we deploy a range of proteomic strategies to identify coccolithogenesis-related proteins. These analyses are supported by a new genome, with gene models derived from long-read transcriptome sequencing, which revealed many novel proteins specific to the calcifying haptophytes. Our experiments provide insights into proteins involved in various aspects of coccolithogenesis. Our improved genome, complemented with transcriptomic and proteomic data, constitutes a new resource for investigating fundamental aspects of coccolithophore biology.
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Affiliation(s)
- Alastair Skeffington
- Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm, 14476, Germany
- Biological and Environmental Sciences, University of Stirling, Stirling, FK9 4LA, UK
| | - Axel Fischer
- Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm, 14476, Germany
| | - Sanja Sviben
- Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm, 14476, Germany
| | - Magdalena Brzezinka
- Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm, 14476, Germany
| | - Michał Górka
- Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm, 14476, Germany
| | - Luca Bertinetti
- Max Planck Institute of Colloids and Interfaces, Potsdam-Golm, 14476, Germany
| | - Christian Woehle
- Max Planck Institute for Plant Breeding Research, Max Planck-Genome-Centre Cologne, Cologne, 50829, Germany
| | - Bruno Huettel
- Max Planck Institute for Plant Breeding Research, Max Planck-Genome-Centre Cologne, Cologne, 50829, Germany
| | - Alexander Graf
- Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm, 14476, Germany
| | - André Scheffel
- Technische Universität Dresden, Faculty of Biology, 01307, Dresden, Germany.
- Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm, 14476, Germany.
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12
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Chang WW, Thies AB, Tresguerres M, Hu MY. Soluble adenylyl cyclase coordinates intracellular pH homeostasis and biomineralization in calcifying cells of a marine animal. Am J Physiol Cell Physiol 2023; 324:C777-C786. [PMID: 36779665 DOI: 10.1152/ajpcell.00524.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023]
Abstract
Biomineralizing cells concentrate dissolved inorganic carbon (DIC) and remove protons from the site of mineral precipitation. However, the molecular regulatory mechanisms that orchestrate pH homeostasis and biomineralization of calcifying cells are poorly understood. Here, we report that the acid-base sensing enzyme soluble adenylyl cyclase (sAC) coordinates intracellular pH (pHi) regulation in the calcifying primary mesenchyme cells (PMCs) of sea urchin larvae. Single-cell transcriptomics, in situ hybridization, and immunocytochemistry elucidated the spatiotemporal expression of sAC during skeletogenesis. Live pHi imaging of PMCs revealed that the downregulation of sAC activity with two structurally unrelated small molecules inhibited pHi regulation of PMCs, an effect that was rescued by the addition of cell-permeable cAMP. Pharmacological sAC inhibition also significantly reduced normal spicule growth and spicule regeneration, establishing a link between PMC pHi regulation and biomineralization. Finally, increased expression of sAC mRNA was detected during skeleton remineralization and exposure to CO2-induced acidification. These findings suggest that transcriptional regulation of sAC is required to promote remineralization and to compensate for acidic stress. This work highlights the central role of sAC in coordinating acid-base regulation and biomineralization in calcifying cells of a marine animal.
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Affiliation(s)
| | - Angus B Thies
- Scripps Institution of Oceanography, University of California San Diego, California, United States
| | - Martin Tresguerres
- Scripps Institution of Oceanography, University of California San Diego, California, United States
| | - Marian Y Hu
- Institute of Physiology, Christian-Albrechts-Universität zu Kiel, Kiel, Germany
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13
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Kholssi R, Lougraimzi H, Moreno-Garrido I. Effects of global environmental change on microalgal photosynthesis, growth and their distribution. MARINE ENVIRONMENTAL RESEARCH 2023; 184:105877. [PMID: 36640723 DOI: 10.1016/j.marenvres.2023.105877] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Revised: 01/06/2023] [Accepted: 01/08/2023] [Indexed: 06/17/2023]
Abstract
Global climate change (GCC) constitutes a complex challenge posing a serious threat to biodiversity and ecosystems in the next decades. There are several recent studies dealing with the potential effect of increased temperature, decrease of pH or shifts in salinity, as well as cascading events of GCC and their impact on human-environment systems. Microalgae as primary producers are a sensitive compartment of the marine ecosystems to all those changes. However, the potential consequences of these changes for marine microalgae have received relatively little attention and they are still not well understood. Thus, there is an urgent need to explore and understand the effects generated by multiple climatic changes on marine microalgae growth and biodiversity. Therefore, this review aimed to compare and contrast mechanisms that marine microalgae exhibit to directly respond to harsh conditions associated with GCC and the potential consequences of those changes in marine microalgal populations. Literature shows that microalgae responses to environmental stressors such as temperature were affected differently. A stress caused by salinity might slow down cell division, reduces size, ceases motility, and triggers palmelloid formation in microalgae community, but some of these changes are strongly species-specific. UV irradiance can potentially lead to an oxidative stress in microalgae, promoting the production of reactive oxygen species (ROS) or induce direct physical damage on microalgae, then inhibiting the growth of microalgae. Moreover, pH could impact many groups of microalgae being more tolerant of certain pH shifts, while others were sensitive to changes of just small units (such as coccolithophorids) and subsequently affect the species at a higher trophic level, but also total vertical carbon transport in oceans. Overall, this review highlights the importance of examining effects of multiple stressors, considering multiple responses to understand the complexity behind stressor interactions.
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Affiliation(s)
- Rajaa Kholssi
- Composting Research Group, Faculty of Sciences, University of Burgos, Burgos, Spain; Ecology and Coastal Management, Institute of Marine Sciences of Andalusia (ICMAN-CSIC), Campus Río San Pedro, 11510, Puerto Real, Cádiz, Spain.
| | - Hanane Lougraimzi
- Laboratory of Plant, Animal and Agro-Industry Productions, Faculty of Sciences, Ibn Tofail University, BP: 242, 14000, Kenitra, Morocco
| | - Ignacio Moreno-Garrido
- Ecology and Coastal Management, Institute of Marine Sciences of Andalusia (ICMAN-CSIC), Campus Río San Pedro, 11510, Puerto Real, Cádiz, Spain
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14
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Chaves G, Ayuyan AG, Cherny VV, Morgan D, Franzen A, Fieber L, Nausch L, Derst C, Mahorivska I, Jardin C, DeCoursey TE, Musset B. Unexpected expansion of the voltage-gated proton channel family. FEBS J 2023; 290:1008-1026. [PMID: 36062330 PMCID: PMC10911540 DOI: 10.1111/febs.16617] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 08/17/2022] [Accepted: 09/02/2022] [Indexed: 11/27/2022]
Abstract
Voltage-gated ion channels, whose first identified function was to generate action potentials, are divided into subfamilies with numerous members. The family of voltage-gated proton channels (HV ) is tiny. To date, all species found to express HV have exclusively one gene that codes for this unique ion channel. Here we report the discovery and characterization of three proton channel genes in the classical model system of neural plasticity, Aplysia californica. The three channels (AcHV 1, AcHV 2, and AcHV 3) are distributed throughout the whole animal. Patch-clamp analysis confirmed proton selectivity of these channels but they all differed markedly in gating. AcHV 1 gating resembled HV in mammalian cells where it is responsible for proton extrusion and charge compensation. AcHV 2 activates more negatively and conducts extensive inward proton current, properties likely to acidify the cytosol. AcHV 3, which differs from AcHV 1 and AcHV 2 in lacking the first arginine in the S4 helix, exhibits proton selective leak currents and weak voltage dependence. We report the expansion of the proton channel family, demonstrating for the first time the expression of three functionally distinct proton channels in a single species.
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Affiliation(s)
- Gustavo Chaves
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Artem G Ayuyan
- Department of Physiology & Biophysics, Rush University, Chicago, IL, USA
| | - Vladimir V Cherny
- Department of Physiology & Biophysics, Rush University, Chicago, IL, USA
| | - Deri Morgan
- Department of Radiation Oncology, University of Kansas Medical Center, MO, USA
| | - Arne Franzen
- Institute of Biological Information Processing, Molecular and Cellular Physiology (IBI-1), Jülich, Germany
| | - Lynne Fieber
- Department of Marine Biology and Ecology - Rosenstiel School of Marine and Atmospheric Science, Miami, FL, USA
| | - Lydia Nausch
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
- Department of Agriculture, Food and Nutrition, Institute of Nutrition and Food Supply Management, University of Applied Sciences Weihenstephan-Triesdorf, Freising, Germany
| | - Christian Derst
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Iryna Mahorivska
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Christophe Jardin
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Thomas E DeCoursey
- Department of Physiology & Biophysics, Rush University, Chicago, IL, USA
| | - Boris Musset
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Salzburg, Austria
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15
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Suárez-Delgado E, Orozco-Contreras M, Rangel-Yescas GE, Islas LD. Activation-pathway transitions in human voltage-gated proton channels revealed by a non-canonical fluorescent amino acid. eLife 2023; 12:85836. [PMID: 36695566 PMCID: PMC9925047 DOI: 10.7554/elife.85836] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Accepted: 01/19/2023] [Indexed: 01/26/2023] Open
Abstract
Voltage-dependent gating of the voltage-gated proton channels (HV1) remains poorly understood, partly because of the difficulty of obtaining direct measurements of voltage sensor movement in the form of gating currents. To circumvent this problem, we have implemented patch-clamp fluorometry in combination with the incorporation of the fluorescent non-canonical amino acid Anap to monitor channel opening and movement of the S4 segment. Simultaneous recording of currents and fluorescence signals allows for direct correlation of these parameters and investigation of their dependence on voltage and the pH gradient (ΔpH). We present data that indicate that Anap incorporated in the S4 helix is quenched by an aromatic residue located in the S2 helix and that motion of the S4 relative to this quencher is responsible for fluorescence increases upon depolarization. The kinetics of the fluorescence signal reveal the existence of a very slow transition in the deactivation pathway, which seems to be singularly regulated by ΔpH. Our experiments also suggest that the voltage sensor can move after channel opening and that the absolute value of the pH can influence the channel opening step. These results shed light on the complexities of voltage-dependent opening of human HV1 channels.
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Affiliation(s)
- Esteban Suárez-Delgado
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México, México City, Mexico
| | - Maru Orozco-Contreras
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México, México City, Mexico
| | - Gisela E Rangel-Yescas
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México, México City, Mexico
| | - Leon D Islas
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México, México City, Mexico
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16
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Telesh IV, Skarlato SO. Harmful Blooms of Potentially Toxic Dinoflagellates in the Baltic Sea: Ecological, Cellular, and Molecular Background. RUSS J ECOL+ 2022. [DOI: 10.1134/s1067413622060157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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17
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Wang X, Li P, Cao X, Liu B, He S, Cao Z, Xing S, Liu L, Li ZH. Effects of ocean acidification and tralopyril on bivalve biomineralization and carbon cycling: A study of the Pacific Oyster (Crassostrea gigas). ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2022; 313:120161. [PMID: 36100119 DOI: 10.1016/j.envpol.2022.120161] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 08/21/2022] [Accepted: 09/08/2022] [Indexed: 06/15/2023]
Abstract
The combined effects of emerging pollutants and ocean acidification (OA) on marine organisms and marine ecosystems have attracted increasing attention. However, the combined effects of tralopyril and OA on marine organisms and marine ecosystems remain unclear. In this study, Crassostrea gigas (C. gigas) were exposed to tralopyril (1 μg/L) and/or OA (PH = 7.7) for 21 days and a 14-day recovery acclimation. To investigate the stress response and potential molecular mechanisms of C. gigas to OA and tralopyril exposure alone or in combination, as well as the effects of OA and/or tralopyril on bivalve biomineralization and marine carbon cycling. The results showed that the combined toxicity was between that of acidification and tralopyril alone. Single or combined exposure activated the general stress defense responses of C. gigas mantle, affected energy metabolism and biomineralization of the organism and the carbon cycle of the marine ecosystem. Moreover, acidification-induced and tralopyril-induced toxicity showed potential recoverability at molecular and biochemical levels. This study provides a new perspective on the molecular mechanisms of tralopyril toxicity to bivalve shellfish and reveals the potential role of tralopyril and OA on marine carbon cycling.
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Affiliation(s)
- Xu Wang
- Marine College, Shandong University, Weihai, Shandong, 264209, China
| | - Ping Li
- Marine College, Shandong University, Weihai, Shandong, 264209, China
| | - Xuqian Cao
- Marine College, Shandong University, Weihai, Shandong, 264209, China
| | - Bin Liu
- Marine College, Shandong University, Weihai, Shandong, 264209, China
| | - Shuwen He
- Marine College, Shandong University, Weihai, Shandong, 264209, China
| | - Zhihan Cao
- Marine College, Shandong University, Weihai, Shandong, 264209, China
| | - Shaoying Xing
- Marine College, Shandong University, Weihai, Shandong, 264209, China
| | - Ling Liu
- Marine College, Shandong University, Weihai, Shandong, 264209, China
| | - Zhi-Hua Li
- Marine College, Shandong University, Weihai, Shandong, 264209, China.
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18
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Wu X, Zhang L, Hong L. The role of Phe150 in human voltage-gated proton channel. iScience 2022; 25:105420. [PMID: 36388967 PMCID: PMC9646954 DOI: 10.1016/j.isci.2022.105420] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 08/15/2022] [Accepted: 10/18/2022] [Indexed: 11/06/2022] Open
Abstract
The voltage-gated proton channel Hv1 is a member of voltage-gated ion channels containing voltage-sensing domains (VSDs). The VSDs are made of four membrane-spanning segments (S1 through S4), and their function is to detect changes in membrane potential in the cells. A highly conserved phenylalanine 150 (F150) is located in the S2 segment of human voltage-gated proton channels. We previously discovered that the F150 is a binding site for the open channel blocker 2GBI. Here, we show that the Hv1 VSD voltage-dependent activation requires a hydrophobic group at position F150. We perform double-mutant cycle analysis to probe interactions between F150 and positively charged arginines in the S4 segment of the channel. Our results indicate that F150 interacts with two arginines (R2 and R3) in the S4 segment and catalyzes the transfer of the S4 arginines in the process of voltage-dependent activation. Hydrophobicity of F150 is crucial for human Hv1 channel voltage-dependent activation F150 interacts with R2 to stabilize the closed state of the Hv1 channel When depolarized, R3 moves upward to interact with F150 stabilizing the open state of Hv1 F150 is essential for the transfer of the Hv1 arginines in the process of voltage sensing
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Affiliation(s)
- Xin Wu
- Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
| | - Lu Zhang
- Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
| | - Liang Hong
- Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, IL 60612, USA
- Corresponding author
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19
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Extracellular carbonic anhydrase activity promotes a carbon concentration mechanism in metazoan calcifying cells. Proc Natl Acad Sci U S A 2022; 119:e2203904119. [PMID: 36161891 DOI: 10.1073/pnas.2203904119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many calcifying organisms utilize metabolic CO2 to generate CaCO3 minerals to harden their shells and skeletons. Carbonic anhydrases are evolutionary ancient enzymes that have been proposed to play a key role in the calcification process, with the underlying mechanisms being little understood. Here, we used the calcifying primary mesenchyme cells (PMCs) of sea urchin larva to study the role of cytosolic (iCAs) and extracellular carbonic anhydrases (eCAs) in the cellular carbon concentration mechanism (CCM). Molecular analyses identified iCAs and eCAs in PMCs and highlight the prominent expression of a glycosylphosphatidylinositol-anchored membrane-bound CA (Cara7). Intracellular pH recordings in combination with CO2 pulse experiments demonstrated iCA activity in PMCs. iCA activity measurements, together with pharmacological approaches, revealed an opposing contribution of iCAs and eCAs on the CCM. H+-selective electrodes were used to demonstrate eCA-catalyzed CO2 hydration rates at the cell surface. Knockdown of Cara7 reduced extracellular CO2 hydration rates accompanied by impaired formation of specific skeletal segments. Finally, reduced pHi regulatory capacities during inhibition and knockdown of Cara7 underscore a role of this eCA in cellular HCO3- uptake. This work reveals the function of CAs in the cellular CCM of a marine calcifying animal. Extracellular hydration of metabolic CO2 by Cara7 coupled to HCO3- uptake mechanisms mitigates the loss of carbon and reduces the cellular proton load during the mineralization process. The findings of this work provide insights into the cellular mechanisms of an ancient biological process that is capable of utilizing CO2 to generate a versatile construction material.
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20
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Leung JYS, Zhang S, Connell SD. Is Ocean Acidification Really a Threat to Marine Calcifiers? A Systematic Review and Meta-Analysis of 980+ Studies Spanning Two Decades. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2107407. [PMID: 35934837 DOI: 10.1002/smll.202107407] [Citation(s) in RCA: 44] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 06/24/2022] [Indexed: 06/15/2023]
Abstract
Ocean acidification is considered detrimental to marine calcifiers, but mounting contradictory evidence suggests a need to revisit this concept. This systematic review and meta-analysis aim to critically re-evaluate the prevailing paradigm of negative effects of ocean acidification on calcifiers. Based on 5153 observations from 985 studies, many calcifiers (e.g., echinoderms, crustaceans, and cephalopods) are found to be tolerant to near-future ocean acidification (pH ≈ 7.8 by the year 2100), but coccolithophores, calcifying algae, and corals appear to be sensitive. Calcifiers are generally more sensitive at the larval stage than adult stage. Over 70% of the observations in growth and calcification are non-negative, implying the acclimation capacity of many calcifiers to ocean acidification. This capacity can be mediated by phenotypic plasticity (e.g., physiological, mineralogical, structural, and molecular adjustments), transgenerational plasticity, increased food availability, or species interactions. The results suggest that the impacts of ocean acidification on calcifiers are less deleterious than initially thought as their adaptability has been underestimated. Therefore, in the forthcoming era of ocean acidification research, it is advocated that studying how marine organisms persist is as important as studying how they perish, and that future hypotheses and experimental designs are not constrained within the paradigm of negative effects.
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Affiliation(s)
- Jonathan Y S Leung
- Faculty of Materials and Energy, Southwest University, Chongqing, 400715, P. R. China
- Southern Seas Ecology Laboratories, School of Biological Sciences, The University of Adelaide, Adelaide, South Australia, 5005, Australia
| | - Sam Zhang
- Faculty of Materials and Energy, Southwest University, Chongqing, 400715, P. R. China
| | - Sean D Connell
- Southern Seas Ecology Laboratories, School of Biological Sciences, The University of Adelaide, Adelaide, South Australia, 5005, Australia
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21
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Voltage-gated proton channels explain coccolithophore sensitivity to ocean acidification. Proc Natl Acad Sci U S A 2022; 119:e2206426119. [PMID: 35687664 PMCID: PMC9231618 DOI: 10.1073/pnas.2206426119] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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22
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Vázquez V, León P, Gordillo FJL, Jiménez C, Concepción I, Mackenzie K, Bresnan E, Segovia M. High-CO 2 Levels Rather than Acidification Restrict Emiliania huxleyi Growth and Performance. MICROBIAL ECOLOGY 2022:10.1007/s00248-022-02035-3. [PMID: 35624343 DOI: 10.1007/s00248-022-02035-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2021] [Accepted: 05/05/2022] [Indexed: 06/15/2023]
Abstract
The coccolithophore Emiliania huxleyi shows a variety of responses to ocean acidification (OA) and to high-CO2 concentrations, but there is still controversy on differentiating between these two factors when using different strains and culture methods. A heavily calcified type A strain isolated from the Norwegian Sea was selected and batch cultured in order to understand whether acclimation to OA was mediated mainly by CO2 or H+, and how it impacted cell growth performance, calcification, and physiological stress management. Emiliania huxleyi responded differently to each acidification method. CO2-enriched aeration (1200 µatm, pH 7.62) induced a negative effect on the cells when compared to acidification caused by decreasing pH alone (pH 7.60). The growth rates of the coccolithophore were more negatively affected by high pCO2 than by low pH without CO2 enrichment with respect to the control (400 µatm, pH 8.1). High CO2 also affected cell viability and promoted the accumulation of reactive oxygen species (ROS), which was not observed under low pH. This suggests a possible metabolic imbalance induced by high CO2 alone. In contrast, the affinity for carbon uptake was negatively affected by both low pH and high CO2. Photochemistry was only marginally affected by either acidification method when analysed by PAM fluorometry. The POC and PIC cellular quotas and the PIC:POC ratio shifted along the different phases of the cultures; consequently, calcification did not follow the same pattern observed in cell stress and growth performance. Specifically, acidification by HCl addition caused a higher proportion of severely deformed coccoliths, than CO2 enrichment. These results highlight the capacity of CO2 rather than acidification itself to generate metabolic stress, not reducing calcification.
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Affiliation(s)
- Víctor Vázquez
- Department of Ecology, Faculty of Sciences, University of Málaga, Boulevard Louis Pasteur S/N, 29071, Málaga, Spain.
| | - Pablo León
- Marine Laboratory, Marine Scotland Science, 375 Victoria Road, Aberdeen, AB11 9DB, UK
| | - Francisco J L Gordillo
- Department of Ecology, Faculty of Sciences, University of Málaga, Boulevard Louis Pasteur S/N, 29071, Málaga, Spain
| | - Carlos Jiménez
- Department of Ecology, Faculty of Sciences, University of Málaga, Boulevard Louis Pasteur S/N, 29071, Málaga, Spain
| | - Iñiguez Concepción
- Department of Ecology, Faculty of Sciences, University of Málaga, Boulevard Louis Pasteur S/N, 29071, Málaga, Spain
| | - Kevin Mackenzie
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, UK
| | - Eileen Bresnan
- Marine Laboratory, Marine Scotland Science, 375 Victoria Road, Aberdeen, AB11 9DB, UK
| | - María Segovia
- Department of Ecology, Faculty of Sciences, University of Málaga, Boulevard Louis Pasteur S/N, 29071, Málaga, Spain
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23
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Reduced H + channel activity disrupts pH homeostasis and calcification in coccolithophores at low ocean pH. Proc Natl Acad Sci U S A 2022; 119:e2118009119. [PMID: 35522711 PMCID: PMC9171652 DOI: 10.1073/pnas.2118009119] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Coccolithophore calcification is a major ocean biogeochemical process. While this process is likely to be sensitive to acidification-driven changes in ocean carbonate chemistry, incomplete understanding of the underlying mechanisms and constraints is a major bottleneck in predicting ocean acidification effects on calcification. We report severe disruption of pH homeostasis linked to a loss of H+ channel function in the coccolithophore Coccolithus braarudii acclimated to seawater pH values that are likely to be encountered currently in localized regions and more widely in future oceans. This disruption leads to specific defects in coccolith morphology. These findings provide mechanistic insight into how calcification in different coccolithophores is affected by changes in seawater carbonate chemistry. Coccolithophores are major producers of ocean biogenic calcite, but this process is predicted to be negatively affected by future ocean acidification scenarios. Since coccolithophores calcify intracellularly, the mechanisms through which changes in seawater carbonate chemistry affect calcification remain unclear. Here we show that voltage-gated H+ channels in the plasma membrane of Coccolithus braarudii serve to regulate pH and maintain calcification under normal conditions but have greatly reduced activity in cells acclimated to low pH. This disrupts intracellular pH homeostasis and impairs the ability of C. braarudii to remove H+ generated by the calcification process, leading to specific coccolith malformations. These coccolith malformations can be reproduced by pharmacological inhibition of H+ channels. Heavily calcified coccolithophore species such as C. braarudii, which make the major contribution to carbonate export to the deep ocean, have a large intracellular H+ load and are likely to be most vulnerable to future decreases in ocean pH.
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24
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Jardin C, Ohlwein N, Franzen A, Chaves G, Musset B. The pH-dependent gating of the human voltage-gated proton channel from computational simulations. Phys Chem Chem Phys 2022; 24:9964-9977. [PMID: 35445675 DOI: 10.1039/d1cp05609c] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Gating of the voltage-gated proton channel HV1 is strongly controlled by pH. There is evidence that this involves the sidechains of titratable amino acids that change their protonation state with changes of the pH. Despite experimental investigations to identify the amino acids involved in pH sensing only few progress has been made, including one histidine at the cytoplasmic side of the channel that is involved in sensing cellular pH. We have used constant pH molecular dynamics simulations in symmetrical and asymmetrical pH conditions across the membrane to investigate the pH- and ΔpH-dependent gating of the human HV1 channel. Therefore, the pKa of every titratable amino acids has been assessed in single simulations. Our simulations captured initial conformational changes between a deactivated and an activated state of the channel induced solely by changes of the pH. The pH-dependent gating is accompanied by an outward displacement of the three S4 voltage sensing arginines that moves the second arginine past the hydrophobic gasket (HG) which separates the inner and outer pores of the channel. HV1 activation, when outer pH increases, involves amino acids at the extracellular entrance of the channel that extend the network of interactions from the external solution down to the HG. Whereas, amino acids at the cytoplasmic entrance of the channel are involved in activation, when inner pH decreases, and in a network of interactions that extend from the cytoplasm up to the HG.
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Affiliation(s)
- Christophe Jardin
- Klinikum Nürnberg Medical School, CPPB, Institute of Physiology, Pathophysiology and Biophysics, Nuremberg, Germany.
| | - Niklas Ohlwein
- Klinikum Nürnberg Medical School, CPPB, Institute of Physiology, Pathophysiology and Biophysics, Nuremberg, Germany. .,Klinik für Anästhesiologie und operative Intensivmedizin, Universitätklinik der Paracelsus Medizinischen Privatuniversität, Nuremberg, Germany
| | - Arne Franzen
- Institute of Biological Information Processing, Molecular and Cellular Physiology (IBI-1), Forschungszentrum Jülich, Jülich, Germany
| | - Gustavo Chaves
- Klinikum Nürnberg Medical School, CPPB, Institute of Physiology, Pathophysiology and Biophysics, Nuremberg, Germany.
| | - Boris Musset
- Klinikum Nürnberg Medical School, CPPB, Institute of Physiology, Pathophysiology and Biophysics, Nuremberg, Germany.
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25
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Wu X, Li Y, Maienschein-Cline M, Feferman L, Wu L, Hong L. RNA-Seq Analyses Reveal Roles of the HVCN1 Proton Channel in Cardiac pH Homeostasis. Front Cell Dev Biol 2022; 10:860502. [PMID: 35372367 PMCID: PMC8967321 DOI: 10.3389/fcell.2022.860502] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Accepted: 02/16/2022] [Indexed: 12/13/2022] Open
Abstract
The voltage-gated proton channel HVCN1 is a member of the voltage-gated ion channel family. HVCN1 channel controls acid extrusion and regulates pH homeostasis in various cell types. Recent evidence indicated that the HVCN1 channel was associated with cardiac function. To investigate the role of HVCN1 in cardiac myocytes, we performed an RNA sequencing analysis of murine hearts and showed that HVCN1 null hearts exhibited a differential transcriptome profile compared with wild-type hearts. The RNA-seq data indicating impaired pH homeostasis in HVCN1 null hearts were the downregulated NADPH oxidoreductases (NOXs) and decreased expression of Cl−/HCO3− exchanger, indicating HVCN1 is a regulator of gene transcriptional networks controlling NOX signaling and CO2 homeostasis in the heart. Additionally, HVCN1 null hearts exhibited differential expression of cardiac ion channels, suggesting a potential role of HVCN1 in cardiac electrophysiological remodeling. The study highlights the importance of HVCN1 in cardiac function and may present a novel target associated with heart diseases.
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Affiliation(s)
- Xin Wu
- Department of Medicine, University of Illinois at Chicago, Chicago, IL, United States
| | - Yawei Li
- Department of Preventive Medicine, Northwestern University, Chicago, IL, United States
| | - Mark Maienschein-Cline
- Research Informatics Core, Research Resources Center, University of Illinois at Chicago, Chicago, IL, United States
| | - Leonid Feferman
- Research Informatics Core, Research Resources Center, University of Illinois at Chicago, Chicago, IL, United States
| | - Longjun Wu
- Department of Neurology, Mayo Clinic, Rochester, MN, United States
| | - Liang Hong
- Department of Medicine, University of Illinois at Chicago, Chicago, IL, United States
- *Correspondence: Liang Hong,
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26
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Gilbert PUPA, Bergmann KD, Boekelheide N, Tambutté S, Mass T, Marin F, Adkins JF, Erez J, Gilbert B, Knutson V, Cantine M, Hernández JO, Knoll AH. Biomineralization: Integrating mechanism and evolutionary history. SCIENCE ADVANCES 2022; 8:eabl9653. [PMID: 35263127 PMCID: PMC8906573 DOI: 10.1126/sciadv.abl9653] [Citation(s) in RCA: 62] [Impact Index Per Article: 31.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Calcium carbonate (CaCO3) biomineralizing organisms have played major roles in the history of life and the global carbon cycle during the past 541 Ma. Both marine diversification and mass extinctions reflect physiological responses to environmental changes through time. An integrated understanding of carbonate biomineralization is necessary to illuminate this evolutionary record and to understand how modern organisms will respond to 21st century global change. Biomineralization evolved independently but convergently across phyla, suggesting a unity of mechanism that transcends biological differences. In this review, we combine CaCO3 skeleton formation mechanisms with constraints from evolutionary history, omics, and a meta-analysis of isotopic data to develop a plausible model for CaCO3 biomineralization applicable to all phyla. The model provides a framework for understanding the environmental sensitivity of marine calcifiers, past mass extinctions, and resilience in 21st century acidifying oceans. Thus, it frames questions about the past, present, and future of CaCO3 biomineralizing organisms.
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Affiliation(s)
- Pupa U. P. A. Gilbert
- Departments of Physics, Chemistry, Geoscience, and Materials Science, University of Wisconsin-Madison, Madison, WI 53706, USA
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Corresponding author. (P.U.P.A.G.); (A.H.K.)
| | - Kristin D. Bergmann
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Nicholas Boekelheide
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Sylvie Tambutté
- Centre Scientifique de Monaco, Department of Marine Biology, 98000 Monaco, Principality of Monaco
| | - Tali Mass
- University of Haifa, Marine Biology Department, Mt. Carmel, Haifa 31905, Israel
| | - Frédéric Marin
- Université de Bourgogne–Franche-Comté (UBFC), Laboratoire Biogéosciences, UMR CNRS 6282, Bâtiment des Sciences Gabriel, 21000 Dijon, France
| | - Jess F. Adkins
- Geological and Planetary Sciences, California Institute of Technology, MS 100-23, Pasadena, CA 91125, USA
| | - Jonathan Erez
- The Hebrew University of Jerusalem, Institute of Earth Sciences, Jerusalem 91904, Israel
| | - Benjamin Gilbert
- Energy Geoscience Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Vanessa Knutson
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Marjorie Cantine
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Goethe-Universität Frankfurt, 60438 Frankfurt am Main, Germany
| | - Javier Ortega Hernández
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Andrew H. Knoll
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
- Corresponding author. (P.U.P.A.G.); (A.H.K.)
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27
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Chaves G, Derst C, Jardin C, Franzen A, Musset B. Voltage-gated proton channels in polyneopteran insects. FEBS Open Bio 2022; 12:523-537. [PMID: 34986517 PMCID: PMC8804609 DOI: 10.1002/2211-5463.13361] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Revised: 12/04/2021] [Accepted: 01/04/2022] [Indexed: 11/17/2022] Open
Abstract
Voltage‐gated proton channels (HV1) are expressed in eukaryotes, including basal hexapods and polyneopteran insects. However, currently, there is little known about HV1 channels in insects. A characteristic aspartate (Asp) that functions as the proton selectivity filter (SF) and the RxWRxxR voltage‐sensor motif are conserved structural elements in HV1 channels. By analysing Transcriptome Shotgun Assembly (TSA) databases, we found 33 polyneopteran species meeting these structural requirements. Unexpectedly, an unusual natural variation Asp to glutamate (Glu) at SF was found in Phasmatodea and Mantophasmatodea. Additionally, we analysed the expression and function of HV1 in the phasmatodean stick insect Extatosoma tiaratum (Et). EtHV1 is strongly expressed in nervous tissue and shows pronounced inward proton conduction. This is the first study of a natural occurring Glu within the SF of a functional HV1 and might be instrumental in uncovering the physiological function of HV1 in insects.
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Affiliation(s)
- Gustavo Chaves
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Christian Derst
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Christophe Jardin
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Arne Franzen
- Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, Forschungszentrum Jülich, Germany
| | - Boris Musset
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany.,Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Salzburg, Austria
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28
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Xie E, Xu K, Li Z, Li W, Yi X, Li H, Han Y, Zhang H, Zhang Y. Disentangling the Effects of Ocean Carbonation and Acidification on Elemental Contents and Macromolecules of the Coccolithophore Emiliania huxleyi. Front Microbiol 2021; 12:737454. [PMID: 34745039 PMCID: PMC8564145 DOI: 10.3389/fmicb.2021.737454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Accepted: 09/29/2021] [Indexed: 11/21/2022] Open
Abstract
Elemental contents change with shifts in macromolecular composition of marine phytoplankton. Recent studies focus on the responses of elemental contents of coccolithophores, a major calcifying phytoplankton group, to changing carbonate chemistry, caused by the dissolution of anthropogenically derived CO2 into the surface ocean. However, the effects of changing carbonate chemistry on biomacromolecules, such as protein and carbohydrate of coccolithophores, are less documented. Here, we disentangled the effects of elevated dissolved inorganic carbon (DIC) concentration (900 to 4,930μmolkg−1) and reduced pH value (8.04 to 7.70) on physiological rates, elemental contents, and macromolecules of the coccolithophore Emiliania huxleyi. Compared to present DIC concentration and pH value, combinations of high DIC concentration and low pH value (ocean acidification) significantly increased pigments content, particulate organic carbon (POC), and carbohydrate content and had less impact on growth rate, maximal relative electron transport rate (rETRmax), particulate organic nitrogen (PON), and protein content. In high pH treatments, elevated DIC concentration significantly increased growth rate, pigments content, rETRmax, POC, particulate inorganic carbon (PIC), protein, and carbohydrate contents. In low pH treatments, the extents of the increase in growth rate, pigments and carbohydrate content were reduced. Compared to high pH value, under low DIC concentration, low pH value significantly increased POC and PON contents and showed less impact on protein and carbohydrate contents; however, under high DIC concentration, low pH value significantly reduced POC, PON, protein, and carbohydrate contents. These results showed that reduced pH counteracted the positive effects of elevated DIC concentration on growth rate, rETRmax, POC, PON, carbohydrate, and protein contents. Elevated DIC concentration and reduced pH acted synergistically to increase the contribution of carbohydrate–carbon to POC, and antagonistically to affect the contribution of protein–nitrogen to PON, which further shifted the carbon/nitrogen ratio of E. huxleyi.
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Affiliation(s)
- Emei Xie
- College of Environmental Science and Engineering, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, China
| | - Kui Xu
- Hubei Key Laboratory of Edible Wild Plants Conservation and Utilization, Hubei Engineering Research Center of Special Wild Vegetables Breeding and Comprehensive Utilization Technology, College of Life Sciences, Hubei Normal University, Huangshi, China
| | - Zhengke Li
- School of Food and Biological Engineering, Shanxi University of Science and Technology, Xi'an, China
| | - Wei Li
- College of Life and Environmental Sciences, Huangshan University, Huangshan, China
| | - Xiangqi Yi
- State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen, China
| | - Hongzhou Li
- College of Environmental Science and Engineering, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, China
| | - Yonghe Han
- College of Environmental Science and Engineering, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, China
| | - Hong Zhang
- College of Environmental Science and Engineering, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, China
| | - Yong Zhang
- College of Environmental Science and Engineering, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, China
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29
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Sokolov VS, Cherny VV, Ayuyan AG, DeCoursey TE. Analysis of an electrostatic mechanism for ΔpH dependent gating of the voltage-gated proton channel, H V1, supports a contribution of protons to gating charge. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2021; 1862:148480. [PMID: 34363792 PMCID: PMC8432343 DOI: 10.1016/j.bbabio.2021.148480] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 07/23/2021] [Accepted: 08/02/2021] [Indexed: 11/23/2022]
Abstract
Voltage-gated proton channels (HV1) resemble the voltage-sensing domain of other voltage-gated ion channels, but differ in containing the conduction pathway. Essential to the functions of HV1 channels in many cells and species is a unique feature called ΔpH dependent gating. The pH on both sides of the membrane strictly regulates the voltage range of channel opening, generally resulting in exclusively outward proton current. Two types of mechanisms could produce ΔpH dependent gating. The "countercharge" mechanism proposes that protons destabilize salt bridges between amino acids in the protein that stabilize specific gating configurations (closed or open). An "electrostatic" mechanism proposes that protons bound to the channel alter the electrical field sensed by the protein. Obligatory proton binding within the membrane electrical field would contribute to measured gating charge. Estimations on the basis of the electrostatic model explain ΔpH dependent gating, but quantitative modeling requires calculations of the electric field inside the protein which, in turn, requires knowledge of its structure. We conclude that both mechanisms operate and contribute to ΔpH dependent gating of HV1.
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Affiliation(s)
- Valerij S Sokolov
- Frumkin Institute of Physical Chemistry and Electrochemistry of Russian Academy of Sciences, Moscow 119071, Russia
| | - Vladimir V Cherny
- Department of Physiology & Biophysics, Rush University, Chicago, IL 60612, USA
| | - Artem G Ayuyan
- Department of Physiology & Biophysics, Rush University, Chicago, IL 60612, USA
| | - Thomas E DeCoursey
- Department of Physiology & Biophysics, Rush University, Chicago, IL 60612, USA.
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30
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Rangel-Yescas G, Cervantes C, Cervantes-Rocha MA, Suárez-Delgado E, Banaszak AT, Maldonado E, Ramsey IS, Rosenbaum T, Islas LD. Discovery and characterization of H v1-type proton channels in reef-building corals. eLife 2021; 10:e69248. [PMID: 34355697 PMCID: PMC8346283 DOI: 10.7554/elife.69248] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 06/30/2021] [Indexed: 12/18/2022] Open
Abstract
Voltage-dependent proton-permeable channels are membrane proteins mediating a number of important physiological functions. Here we report the presence of a gene encoding Hv1 voltage-dependent, proton-permeable channels in two species of reef-building corals. We performed a characterization of their biophysical properties and found that these channels are fast-activating and modulated by the pH gradient in a distinct manner. The biophysical properties of these novel channels make them interesting model systems. We have also developed an allosteric gating model that provides mechanistic insight into the modulation of voltage-dependence by protons. This work also represents the first functional characterization of any ion channel in scleractinian corals. We discuss the implications of the presence of these channels in the membranes of coral cells in the calcification and pH-regulation processes and possible consequences of ocean acidification related to the function of these channels.
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Affiliation(s)
- Gisela Rangel-Yescas
- Departmento de Fisiología, Facultad of Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Cecilia Cervantes
- Departmento de Fisiología, Facultad of Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Miguel A Cervantes-Rocha
- Departmento de Fisiología, Facultad of Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Esteban Suárez-Delgado
- Departmento de Fisiología, Facultad of Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Anastazia T Banaszak
- Unidad Académica de Sistemas Arrecifales, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Puerto Morelos, Mexico
| | - Ernesto Maldonado
- EvoDevo Research Group, Unidad Académica de Sistemas Arrecifales, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Puerto Morelos, Mexico
| | - Ian Scott Ramsey
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, United States
| | - Tamara Rosenbaum
- Departmento of Neurociencia Cognitiva, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Leon D Islas
- Departmento de Fisiología, Facultad of Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
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31
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An otopetrin family proton channel promotes cellular acid efflux critical for biomineralization in a marine calcifier. Proc Natl Acad Sci U S A 2021; 118:2101378118. [PMID: 34301868 DOI: 10.1073/pnas.2101378118] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Otopetrins comprise a family of proton-selective channels that are critically important for the mineralization of otoliths and statoconia in vertebrates but whose underlying cellular mechanisms remain largely unknown. Here, we demonstrate that otopetrins are critically involved in the calcification process by providing an exit route for protons liberated by the formation of CaCO3 Using the sea urchin larva, we examined the otopetrin ortholog otop2l, which is exclusively expressed in the calcifying primary mesenchymal cells (PMCs) that generate the calcitic larval skeleton. otop2l expression is stimulated during skeletogenesis, and knockdown of otop2l impairs spicule formation. Intracellular pH measurements demonstrated Zn2+-sensitive H+ fluxes in PMCs that regulate intracellular pH in a Na+/HCO3 --independent manner, while Otop2l knockdown reduced membrane proton permeability. Furthermore, Otop2l displays unique features, including strong activation by high extracellular pH (>8.0) and check-valve-like outwardly rectifying H+ flux properties, making it into a cellular proton extrusion machine adapted to oceanic living conditions. Our results provide evidence that otopetrin family proton channels are a central component of the cellular pH regulatory machinery in biomineralizing cells. Their ubiquitous occurrence in calcifying systems across the animal kingdom suggest a conserved physiological function by mediating pH at the site of mineralization. This important role of otopetrin family proton channels has strong implications for our view on the cellular mechanisms of biomineralization and their response to changes in oceanic pH.
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32
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Abstract
Mollusc shells are a result of the deposition of crystalline and amorphous calcite catalysed by enzymes and shell matrix proteins. Developing a detailed understanding of bivalve mollusc biomineralization pathways is complicated not only by the multiplicity of shell forms and microstructures in this class, but also by the evolution of associated proteins by domain co-option and domain shuffling. In spite of this, a minimal biomineralization toolbox comprising proteins and protein domains critical for shell production across species has been identified. Using a matched pair design to reduce experimental noise from inter-individual variation, combined with damage-repair experiments and a database of biomineralization shell matrix proteins (SMP) derived from published works, proteins were identified that are likely to be involved in shell calcification. Eighteen new, shared proteins likely to be involved in the processes related to the calcification of shells were identified by analysis of genes expressed during repair in Crassostrea gigas, Mytilus edulis and Pecten maximus. Genes involved in ion transport were also identified as potentially involved in calcification either via the maintenance of cell acid-base balance or transport of critical ions to the extrapallial space, the site of shell assembly. These data expand the number of candidate biomineralization proteins in bivalve molluscs for future functional studies and define a minimal functional protein domain set required to produce solid microstructures from soluble calcium carbonate. This is important for understanding molluscan shell evolution, the likely impacts of environmental change on biomineralization processes, materials science, and biomimicry research.
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Affiliation(s)
- Tejaswi Yarra
- University of Edinburgh, Institute of Evolutionary Biology, Ashworth Laboratories, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.,British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
| | - Mark Blaxter
- Sanger Institute, Wellcome Genome Campus, Hinxton, Cambridgeshire, CB10 1SA, UK
| | - Melody S Clark
- British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
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33
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Zhang Y, Gao K. Photosynthesis and calcification of the coccolithophore Emiliania huxleyi are more sensitive to changed levels of light and CO 2 under nutrient limitation. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2021; 217:112145. [PMID: 33735745 DOI: 10.1016/j.jphotobiol.2021.112145] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 01/02/2021] [Accepted: 01/25/2021] [Indexed: 11/18/2022]
Abstract
Photophysiological responses of phytoplankton to changing multiple environmental drivers are essential in understanding and predicting ecological consequences of ocean climate changes. In this study, we investigated the combined effects of two CO2 levels (410 and 925 μatm) and five light intensities (80 to 480 μmol photons m-2 s-1) on cellular pigments contents, photosynthesis and calcification of the coccolithophore Emiliania huxleyi grown under nutrient replete and limited conditions, respectively. Our results showed that high light intensity, high CO2 level and nitrate limitation acted synergistically to reduce cellular chlorophyll a and carotenoid contents. Nitrate limitation predominantly enhanced calcification rate; phosphate limitation predominantly reduced photosynthetic carbon fixation rate, with larger extent of the reduction under higher levels of CO2 and light. Reduced availability of both nitrate and phosphate under the elevated CO2 concentration decreased saturating light levels for the cells to achieve the maximal relative electron transport rate (rETRmax). Light-saturating levels for rETRmax were lower than that for photosynthetic and calcification rates under the nutrient limitation. Regardless of the culture conditions, rETR under growth light levels correlated linearly and positively with measured photosynthetic and calcification rates. Our findings imply that E. huxleyi cells acclimated to macro-nutrient limitation and elevated CO2 concentration decreased their light requirement to achieve the maximal electron transport, photosynthetic and calcification rates, indicating a photophysiological strategy to cope with CO2 rise/pH drop in shoaled upper mixing layer above the thermocline where the microalgal cells are exposed to increased levels of light and decreased levels of nutrients.
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Affiliation(s)
- Yong Zhang
- State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen, China; College of Environmental Science and Engineering, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, China
| | - Kunshan Gao
- State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen, China; Co-Innovation Center of Jiangsu Marine Bio-industry Technology, Jiangsu Ocean University, Lianyungang 222005, China.
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34
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Capasso L, Ganot P, Planas-Bielsa V, Tambutté S, Zoccola D. Intracellular pH regulation: characterization and functional investigation of H + transporters in Stylophora pistillata. BMC Mol Cell Biol 2021; 22:18. [PMID: 33685406 PMCID: PMC7941709 DOI: 10.1186/s12860-021-00353-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 02/22/2021] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Reef-building corals regularly experience changes in intra- and extracellular H+ concentrations ([H+]) due to physiological and environmental processes. Stringent control of [H+] is required to maintain the homeostatic acid-base balance in coral cells and is achieved through the regulation of intracellular pH (pHi). This task is especially challenging for reef-building corals that share an endosymbiotic relationship with photosynthetic dinoflagellates (family Symbiodinaceae), which significantly affect the pHi of coral cells. Despite their importance, the pH regulatory proteins involved in the homeostatic acid-base balance have been scarcely investigated in corals. Here, we report in the coral Stylophora pistillata a full characterization of the genomic structure, domain topology and phylogeny of three major H+ transporter families that are known to play a role in the intracellular pH regulation of animal cells; we investigated their tissue-specific expression patterns and assessed the effect of seawater acidification on their expression levels. RESULTS We identified members of the Na+/H+ exchanger (SLC9), vacuolar-type electrogenic H+-ATP hydrolase (V-ATPase) and voltage-gated proton channel (HvCN) families in the genome and transcriptome of S. pistillata. In addition, we identified a novel member of the HvCN gene family in the cnidarian subclass Hexacorallia that has not been previously described in any species. We also identified key residues that contribute to H+ transporter substrate specificity, protein function and regulation. Last, we demonstrated that some of these proteins have different tissue expression patterns, and most are unaffected by exposure to seawater acidification. CONCLUSIONS In this study, we provide the first characterization of H+ transporters that might contribute to the homeostatic acid-base balance in coral cells. This work will enrich the knowledge of the basic aspects of coral biology and has important implications for our understanding of how corals regulate their intracellular environment.
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Affiliation(s)
- Laura Capasso
- Centre Scientifique de Monaco, 8 quai Antoine 1er, 98000, Monaco, Monaco.,Sorbonne Université, Collège Doctoral, F-75005, Paris, France
| | - Philippe Ganot
- Centre Scientifique de Monaco, 8 quai Antoine 1er, 98000, Monaco, Monaco
| | | | - Sylvie Tambutté
- Centre Scientifique de Monaco, 8 quai Antoine 1er, 98000, Monaco, Monaco
| | - Didier Zoccola
- Centre Scientifique de Monaco, 8 quai Antoine 1er, 98000, Monaco, Monaco.
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35
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He X, Ding F, Sun X, Zheng Y, Xu W, Ye L, Chen H, Shen J. Reversible Chemosensor for Bioimaging and Biosensing of Zn(II) and hpH in Cells, Larval Zebrafish, and Plants with Dual-Channel Fluorescence Signals. Inorg Chem 2021; 60:5563-5572. [PMID: 33667336 DOI: 10.1021/acs.inorgchem.0c03456] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Zinc/Zn(II) is an essential trace element for humans and acts as an important substance that maintains the normal growth, development, and metabolism of the body. Excess or deficient Zn(II) can cause abnormal metabolism in the human body, leading to a series of diseases. Moreover, biosystems have complex homeostasis systems, especially harsh pH (OH-) environments. Thus, investigating the variation in the levels of Zn(II) and OH- is extremely important in clinical, medical, and environmental testing. Nevertheless, the lack of practical and convenient fluorescence imaging tools limits the tracing of Zn(II) and OH- in biosystems. In this work, a well-designed dual-channel fluorescent signal response chemosensor (DACH-fhba) was assembled for selective sensing of Zn(II) and OH- in the biosystem using a fluorescence turn-on strategy. On encountering Zn(II), the chemosensor emitted a blue fluorescence signal (455 nm). Meanwhile, the bright green fluorescence signal (530 nm) increased with OH- addition simultaneously. With the blue/green dual fluorescence response of DACH-fhba, the sensor exhibited high stability and reversibility. Notably, the bioimaging revealed that DACH-fhba successfully tracked Zn(II) and OH- in live cells, larval zebrafish, and plants. Further results implied that DACH-fhba can be used to achieve visual detection of Zn(II) and OH- in organisms. Altogether, this work is conducive to the monitoring of Zn(II) and OH- in organisms and promotes the understanding of the function of Zn(II) and OH- in biosystems.
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Affiliation(s)
- Xiaojun He
- School of Ophthalmology & Optometry, School of Biomedical Engineering, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China
| | - Feng Ding
- Department of Microbiology & Immunology, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China
| | - Xiaoshuai Sun
- School of Ophthalmology & Optometry, School of Biomedical Engineering, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China
| | - Yujing Zheng
- School of Ophthalmology & Optometry, School of Biomedical Engineering, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China
| | - Wei Xu
- School of Ophthalmology & Optometry, School of Biomedical Engineering, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China
| | - Lisong Ye
- School of Ophthalmology & Optometry, School of Biomedical Engineering, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China
| | - Hong Chen
- College of Food and Drug, Henan Functional Cosmetics Engineering & Technology Research Center, Luoyang Normal University, Luoyang, Henan 471934, China
| | - Jianliang Shen
- School of Ophthalmology & Optometry, School of Biomedical Engineering, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China.,Engineering Research Center of Clinical Functional Materials and Diagnosis & Treatment Devices of Zhejiang Province, Wenzhou Institute, University of Chinese Academy of Sciences, Wenzhou, Zhejiang 325001, China
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36
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Brownlee C, Langer G, Wheeler GL. Coccolithophore calcification: Changing paradigms in changing oceans. Acta Biomater 2021; 120:4-11. [PMID: 32763469 DOI: 10.1016/j.actbio.2020.07.050] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 07/13/2020] [Accepted: 07/26/2020] [Indexed: 11/30/2022]
Abstract
Coccolithophores represent a major component of the marine phytoplankton and contribute to the bulk of biogenic calcite formation on Earth. These unicellular protists produce minute calcite scales (coccoliths) within the cell, which are secreted to the cell surface. Individual coccoliths and their arrangements on the cell surface display a wide range of morphological variations. This review explores some of the recent evidence that points to similarities and differences in the mechanisms of calcification, focussing on the transport mechanisms that bring substrates to, and remove products from the site of calcification, together with new findings on factors that regulate coccolith morphology. We argue that better knowledge of these mechanisms and their variations is needed to inform more generally how different species of coccolithophore are likely to respond to changes in ocean chemistry. STATEMENT OF SIGNIFICANCE: Coccolithophores, minute single celled phytoplankton are the major producers of biogenic carbonate on Earth. They also represent an important component of the ocean's biota and contribute significantly to global carbon fluxes. Coccolithophores produce intricate calcite scales (coccoliths) internally that they secrete onto their external surface. This review presents some recent key findings on the mechanisms underlying the production of coccoliths. It also considers the factors that regulate the rate of production as well as the variety of shapes of individual coccoliths and their arrangements at the cell surface. Understanding these processes is needed to allow better predictions of how coccolithophores may respond to changing ocean chemistry associated with climate change.
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Affiliation(s)
- Colin Brownlee
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK; School of Ocean and Earth Sciences, University of Southampton, Southampton SO14 3ZH, UK.
| | - Gerald Langer
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK
| | - Glen L Wheeler
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK
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Voltage and pH difference across the membrane control the S4 voltage-sensor motion of the Hv1 proton channel. Sci Rep 2020; 10:21293. [PMID: 33277511 PMCID: PMC7718894 DOI: 10.1038/s41598-020-77986-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 10/28/2020] [Indexed: 12/26/2022] Open
Abstract
The voltage-gated proton channel Hv1 is expressed in a variety of cells, including macrophages, sperm, and lung epithelial cells. Hv1 is gated by both the membrane potential and the difference between the intra- and extracellular pH (ΔpH). The coupling of voltage- and ∆pH-sensing is such that Hv1 opens only when the electrochemical proton gradient is outwardly directed. However, the molecular mechanism of this coupling is not known. Here, we investigate the coupling between voltage- and ΔpH-sensing of Ciona intestinalis proton channel (ciHv1) using patch-clamp fluorometry (PCF) and proton uncaging. We show that changes in ΔpH can induce conformational changes of the S4 voltage sensor. Our results are consistent with the idea that S4 can detect both voltage and ΔpH.
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Wege S, De Angeli A. Novel Electrical Signaling: First Fast Voltage-Gated Sodium Channel Identified Outside of the Animal Kingdom. PLANT PHYSIOLOGY 2020; 184:1618-1619. [PMID: 33277327 PMCID: PMC7723076 DOI: 10.1104/pp.20.01400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Affiliation(s)
- Stefanie Wege
- Australian Research Council Centre of Excellence in Plant Energy Biology, Plant Research Centre, School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Waite Campus, Glen Osmond 5064, South Australia, Australia
| | - Alexis De Angeli
- Biochemistry and Plant Molecular Physiology, Université de Montpellier, Centre National de la Recherche Scientifique, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement, Institut Agro, Montpellier 34060, France
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Seifert M, Rost B, Trimborn S, Hauck J. Meta-analysis of multiple driver effects on marine phytoplankton highlights modulating role of pCO 2. GLOBAL CHANGE BIOLOGY 2020; 26:6787-6804. [PMID: 32905664 DOI: 10.1111/gcb.15341] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 08/26/2020] [Accepted: 08/26/2020] [Indexed: 06/11/2023]
Abstract
Responses of marine primary production to a changing climate are determined by a concert of multiple environmental changes, for example in temperature, light, pCO2 , nutrients, and grazing. To make robust projections of future global marine primary production, it is crucial to understand multiple driver effects on phytoplankton. This meta-analysis quantifies individual and interactive effects of dual driver combinations on marine phytoplankton growth rates. Almost 50% of the single-species laboratory studies were excluded because central data and metadata (growth rates, carbonate system, experimental treatments) were insufficiently reported. The remaining data (42 studies) allowed for the analysis of interactions of pCO2 with temperature, light, and nutrients, respectively. Growth rates mostly respond non-additively, whereby the interaction with increased pCO2 profusely dampens growth-enhancing effects of high temperature and high light. Multiple and single driver effects on coccolithophores differ from other phytoplankton groups, especially in their high sensitivity to increasing pCO2 . Polar species decrease their growth rate in response to high pCO2 , while temperate and tropical species benefit under these conditions. Based on the observed interactions and projected changes, we anticipate primary productivity to: (a) first increase but eventually decrease in the Arctic Ocean once nutrient limitation outweighs the benefits of higher light availability; (b) decrease in the tropics and mid-latitudes due to intensifying nutrient limitation, possibly amplified by elevated pCO2 ; and (c) increase in the Southern Ocean in view of higher nutrient availability and synergistic interaction with increasing pCO2 . Growth-enhancing effect of high light and warming to coccolithophores, mainly Emiliania huxleyi, might increase their relative abundance as long as not offset by acidification. Dinoflagellates are expected to increase their relative abundance due to their positive growth response to increasing pCO2 and light levels. Our analysis reveals gaps in the knowledge on multiple driver responses and provides recommendations for future work on phytoplankton.
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Affiliation(s)
- Miriam Seifert
- Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
| | - Björn Rost
- Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
- Universität Bremen, Bremen, Germany
| | - Scarlett Trimborn
- Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
- Universität Bremen, Bremen, Germany
| | - Judith Hauck
- Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
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40
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Helliwell KE, Chrachri A, Koester JA, Wharam S, Taylor AR, Wheeler GL, Brownlee C. A Novel Single-Domain Na +-Selective Voltage-Gated Channel in Photosynthetic Eukaryotes. PLANT PHYSIOLOGY 2020; 184:1674-1683. [PMID: 33004614 PMCID: PMC7723092 DOI: 10.1104/pp.20.00889] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Accepted: 09/15/2020] [Indexed: 06/11/2023]
Abstract
The evolution of Na+-selective four-domain voltage-gated channels (4D-Navs) in animals allowed rapid Na+-dependent electrical excitability, and enabled the development of sophisticated systems for rapid and long-range signaling. While bacteria encode single-domain Na+-selective voltage-gated channels (BacNav), they typically exhibit much slower kinetics than 4D-Navs, and are not thought to have crossed the prokaryote-eukaryote boundary. As such, the capacity for rapid Na+-selective signaling is considered to be confined to certain animal taxa, and absent from photosynthetic eukaryotes. Certainly, in land plants, such as the Venus flytrap (Dionaea muscipula) where fast electrical excitability has been described, this is most likely based on fast anion channels. Here, we report a unique class of eukaryotic Na+-selective, single-domain channels (EukCatBs) that are present primarily in haptophyte algae, including the ecologically important calcifying coccolithophores, Emiliania huxleyi and Scyphosphaera apsteinii The EukCatB channels exhibit very rapid voltage-dependent activation and inactivation kinetics, and isoform-specific sensitivity to the highly selective 4D-Nav blocker tetrodotoxin. The results demonstrate that the capacity for rapid Na+-based signaling in eukaryotes is not restricted to animals or to the presence of 4D-Navs. The EukCatB channels therefore represent an independent evolution of fast Na+-based electrical signaling in eukaryotes that likely contribute to sophisticated cellular control mechanisms operating on very short time scales in unicellular algae.
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Affiliation(s)
- Katherine E Helliwell
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, United Kingdom
- Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4QD United Kingdom
| | - Abdul Chrachri
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, United Kingdom
| | - Julie A Koester
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina 28403-591
| | - Susan Wharam
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, United Kingdom
| | - Alison R Taylor
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina 28403-591
| | - Glen L Wheeler
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, United Kingdom
| | - Colin Brownlee
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, United Kingdom
- School of Ocean and Earth Science, University of Southampton, Southampton, SO14 3ZH, United Kingdom
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41
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Paul AJ, Bach LT. Universal response pattern of phytoplankton growth rates to increasing CO 2. THE NEW PHYTOLOGIST 2020; 228:1710-1716. [PMID: 32654139 DOI: 10.1111/nph.16806] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Accepted: 06/28/2020] [Indexed: 06/11/2023]
Abstract
Phytoplankton growth rate is a key variable controlling species succession and ecosystem structure throughout the surface ocean. Carbonate chemistry conditions are known to influence phytoplankton growth rates but there is no conceptual framework allowing us to compare growth rate responses across taxa. Here we analyse the literature to show that phytoplankton growth rates follow an optimum curve response pattern whenever the tested species is exposed to a sufficiently large gradient in proton (H+ ) concentrations. Based on previous findings with coccolithophores and diatoms, we argue that this 'universal reaction norm' is shaped by the stimulating influence of increasing inorganic carbon substrate (left side of the optimum) and the inhibiting influence of increase H+ (right side of the optimum). We envisage that exploration of carbonate chemistry-dependent optimum curves as a default experimental approach will boost our mechanistic understanding of phytoplankton responses to ocean acidification, like temperature curves have already boosted our mechanistic understanding to global warming.
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Affiliation(s)
- Allanah J Paul
- Marine Biogeochemistry, GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105, Kiel, Germany
| | - Lennart T Bach
- Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Tasmania, 7004, Australia
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42
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Feng Y, Roleda MY, Armstrong E, Summerfield TC, Law CS, Hurd CL, Boyd PW. Effects of multiple drivers of ocean global change on the physiology and functional gene expression of the coccolithophore Emiliania huxleyi. GLOBAL CHANGE BIOLOGY 2020; 26:5630-5645. [PMID: 32597547 DOI: 10.1111/gcb.15259] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 06/04/2020] [Accepted: 06/13/2020] [Indexed: 06/11/2023]
Abstract
Ongoing ocean global change due to anthropogenic activities is causing multiple chemical and physical seawater properties to change simultaneously, which may affect the physiology of marine phytoplankton. The coccolithophore Emiliania huxleyi is a model species often employed in the study of the marine carbon cycle. The effect of ocean acidification (OA) on coccolithophore calcification has been extensively studied; however, physiological responses to multiple environmental drivers are still largely unknown. Here we examined two-way and multiple driver effects of OA and other key environmental drivers-nitrate, phosphate, irradiance, and temperature-on the growth, photosynthetic, and calcification rates, and the elemental composition of E. huxleyi. In addition, changes in functional gene expression were examined to understand the molecular mechanisms underpinning the physiological responses. The single driver manipulation experiments suggest decreased nitrate supply being the most important driver regulating E. huxleyi physiology, by significantly reducing the growth, photosynthetic, and calcification rates. In addition, the interaction of OA and decreased nitrate supply (projected for year 2100) had more negative synergistic effects on E. huxleyi physiology than all other two-way factorial manipulations, suggesting a linkage between the single dominant driver (nitrate) effects and interactive effects with other drivers. Simultaneous manipulation of all five environmental drivers to the conditions of the projected year 2100 had the largest negative effects on most of the physiological metrics. Furthermore, functional genes associated with inorganic carbon acquisition (RubisCO, AEL1, and δCA) and calcification (CAX3, AEL1, PATP, and NhaA2) were most downregulated by the multiple driver manipulation, revealing linkages between responses of functional gene expression and associated physiological metrics. These findings together indicate that for more holistic projections of coccolithophore responses to future ocean global change, it is necessary to understand the relative importance of environmental drivers both individually (i.e., mechanistic understanding) and interactively (i.e., cumulative effect) on coccolithophore physiology.
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Affiliation(s)
- Yuanyuan Feng
- College of Marine and Environmental Sciences, Tianjin University of Science and Technology, Tianjin, China
- Department of Botany, University of Otago, Dunedin, New Zealand
| | - Michael Y Roleda
- Department of Botany, University of Otago, Dunedin, New Zealand
- The Marine Science Institute, University of the Philippines, Quezon City, Philippines
| | - Evelyn Armstrong
- NIWA/University of Otago Research Centre for Oceanography, Department of Chemistry, University of Otago, Dunedin, New Zealand
| | | | - Cliff S Law
- NIWA/University of Otago Research Centre for Oceanography, Department of Chemistry, University of Otago, Dunedin, New Zealand
- National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand
| | - Catriona L Hurd
- Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tas., Australia
| | - Philip W Boyd
- Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tas., Australia
- Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tas., Australia
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43
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Hu MY, Petersen I, Chang WW, Blurton C, Stumpp M. Cellular bicarbonate accumulation and vesicular proton transport promote calcification in the sea urchin larva. Proc Biol Sci 2020; 287:20201506. [PMID: 32900308 PMCID: PMC7542784 DOI: 10.1098/rspb.2020.1506] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Accepted: 08/07/2020] [Indexed: 12/12/2022] Open
Abstract
The sea urchin embryo develops a calcitic endoskeleton through intracellular formation of amorphous calcium carbonate (ACC). Intracellular precipitation of ACC, requires [Formula: see text] concentrating as well as proton export mechanisms to promote calcification. These processes are of fundamental importance in biological mineralization, but remain largely unexplored. Here, we demonstrate that the calcifying primary mesenchyme cells (PMCs) use Na+/H+-exchange (NHE) mechanisms to control cellular pH homeostasis during maintenance of the skeleton. During skeleton re-calcification, pHi of PMCs is increased accompanied by substantial elevation in intracellular [Formula: see text] mediated by the [Formula: see text] cotransporter Sp_Slc4a10. However, PMCs lower their pHi regulatory capacities associated with a reduction in NHE activity. Live-cell imaging using green fluorescent protein reporter constructs in combination with intravesicular pH measurements demonstrated alkaline and acidic populations of vesicles in PMCs and extensive trafficking of large V-type H+-ATPase (VHA)-rich acidic vesicles in blastocoelar filopodial cells. Pharmacological and gene expression analyses underline a central role of the VHA isoforms Sp_ATP6V0a1, Sp_ATP6V01_1 and Sp_ATPa1-4 for the process of skeleton re-calcification. These results highlight novel pH regulatory strategies in calcifying cells of a marine species with important implications for our understanding of the mineralization process in times of rapid changes in oceanic pH.
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Affiliation(s)
- Marian Y. Hu
- Institute of Physiology, Christian-Albrechts-University Kiel, Hermann-Rodewaldstraße 5, 24118 Kiel, Germany
| | - Inga Petersen
- Institute of Physiology, Christian-Albrechts-University Kiel, Hermann-Rodewaldstraße 5, 24118 Kiel, Germany
| | - William Weijen Chang
- Institute of Physiology, Christian-Albrechts-University Kiel, Hermann-Rodewaldstraße 5, 24118 Kiel, Germany
| | - Christine Blurton
- Institute of Immunobiology, Christian-Albrechts-University Kiel, Am Botanischen Garten 1-9, 24118 Kiel, Germany
| | - Meike Stumpp
- Institute of Immunobiology, Christian-Albrechts-University Kiel, Am Botanischen Garten 1-9, 24118 Kiel, Germany
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44
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Chaves G, Bungert-Plümke S, Franzen A, Mahorivska I, Musset B. Zinc modulation of proton currents in a new voltage-gated proton channel suggests a mechanism of inhibition. FEBS J 2020; 287:4996-5018. [PMID: 32160407 PMCID: PMC7754295 DOI: 10.1111/febs.15291] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 01/10/2020] [Accepted: 03/10/2020] [Indexed: 02/03/2023]
Abstract
The HV1 voltage‐gated proton (HV1) channel is a key component of the cellular proton extrusion machinery and is pivotal for charge compensation during the respiratory burst of phagocytes. The best‐described physiological inhibitor of HV1 is Zn2+. Externally applied ZnCl2 drastically reduces proton currents reportedly recorded in Homo sapiens, Rattus norvegicus, Mus musculus, Oryctolagus cuniculus, Rana esculenta, Helix aspersa, Ciona intestinalis, Coccolithus pelagicus, Emiliania huxleyi, Danio rerio, Helisoma trivolvis, and Lingulodinium polyedrum, but with considerable species variability. Here, we report the effects of Zn2+ and Cd2+ on HV1 from Nicoletia phytophila, NpHV1. We introduced mutations at potential Zn2+ coordination sites and measured Zn2+ inhibition in different extracellular pH, with Zn2+ concentrations up to 1000 μm. Zn2+ inhibition in NpHV1 was quantified by the slowing of the activation time constant and a positive shift of the conductance–voltage curve. Replacing aspartate in the S3‐S4 loop with histidine (D145H) enhanced both the slowing of activation kinetics and the shift in the voltage–conductance curve, such that Zn2+ inhibition closely resembled that of the human channel. Histidine is much more effective than aspartate in coordinating Zn2+ in the S3‐S4 linker. A simple Hodgkin Huxley model of NpHV1 suggests a decrease in the opening rate if it is inhibited by zinc or cadmium. Limiting slope measurements and high‐resolution clear native gel electrophoresis (hrCNE) confirmed that NpHV1 functions as a dimer. The data support the hypothesis that zinc is coordinated in between the dimer instead of the monomer. Zinc coordination sites may be potential targets for drug development.
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Affiliation(s)
- Gustavo Chaves
- Institut für Physiologie und Pathophysiologie, Paracelsus Universität Salzburg Standort Nürnberg, Nuremberg, Germany
| | - Stefanie Bungert-Plümke
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4) Forschungszentrum Jülich, Jülich, Germany
| | - Arne Franzen
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4) Forschungszentrum Jülich, Jülich, Germany
| | - Iryna Mahorivska
- Institut für Physiologie und Pathophysiologie, Paracelsus Universität Salzburg Standort Nürnberg, Nuremberg, Germany
| | - Boris Musset
- Institut für Physiologie und Pathophysiologie, Paracelsus Universität Salzburg Standort Nürnberg, Nuremberg, Germany
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45
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Kadan Y, Aram L, Shimoni E, Levin-Zaidman S, Rosenwasser S, Gal A. In situ electron microscopy characterization of intracellular ion pools in mineral forming microalgae. J Struct Biol 2020; 210:107465. [DOI: 10.1016/j.jsb.2020.107465] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2019] [Revised: 01/13/2020] [Accepted: 01/17/2020] [Indexed: 12/19/2022]
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46
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Chandra Rajan K, Vengatesen T. Molecular adaptation of molluscan biomineralisation to high-CO 2 oceans - The known and the unknown. MARINE ENVIRONMENTAL RESEARCH 2020; 155:104883. [PMID: 32072987 DOI: 10.1016/j.marenvres.2020.104883] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2019] [Revised: 01/11/2020] [Accepted: 01/19/2020] [Indexed: 06/10/2023]
Abstract
High-CO2 induced ocean acidification (OA) reduces the calcium carbonate (CaCO3) saturation level (Ω) and the pH of oceans. Consequently, OA is causing a serious threat to several ecologically and economically important biomineralising molluscs. Biomineralisation is a highly controlled biochemical process by which molluscs deposit their calcareous structures. In this process, shell matrix proteins aid the nucleation, growth and assemblage of the CaCO3 crystals in the shell. These molluscan shell proteins (MSPs) are, ultimately, responsible for determination of the diverse shell microstructures and mechanical strength. Recent studies have attempted to integrate gene and protein expression data of MSPs with shell structure and mechanical properties. These advances made in understanding the molecular mechanism of biomineralisation suggest that molluscs either succumb or adapt to OA stress. In this review, we discuss the fate of biomineralisation process in future high-CO2 oceans and its ultimate impact on the mineralised shell's structure and mechanical properties from the perspectives of limited substrate availability theory, proton flux limitation model and the omega myth theory. Furthermore, studying the interplay of energy availability and differential gene expression is an essential first step towards understanding adaptation of molluscan biomineralisation to OA, because if there is a need to change gene expression under stressors, any living system would require more energy than usual. To conclude, we have listed, four important future research directions for molecular adaptation of molluscan biomineralisation in high-CO2 oceans: 1) Including an energy budgeting factor while understanding differential gene expression of MSPs and ion transporters under OA. 2) Unraveling the genetic or epigenetic changes related to biomineralisation under stressors to help solving a bigger picture about future evolution of molluscs, and 3) Understanding Post Translational Modifications of MSPs with and without stressors. 4) Understanding carbon uptake mechanisms across taxa with and without OA to clarify the OA theories on Ω.
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Affiliation(s)
- Kanmani Chandra Rajan
- The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China; State Key Laboratory of Marine Pollution, Hong Kong SAR, China.
| | - Thiyagarajan Vengatesen
- The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China; State Key Laboratory of Marine Pollution, Hong Kong SAR, China.
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47
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Jardin C, Chaves G, Musset B. Assessing Structural Determinants of Zn 2+ Binding to Human H V1 via Multiple MD Simulations. Biophys J 2020; 118:1221-1233. [PMID: 31972155 DOI: 10.1016/j.bpj.2019.12.035] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 12/20/2019] [Accepted: 12/27/2019] [Indexed: 01/02/2023] Open
Abstract
Voltage-gated proton channels (HV1) are essential for various physiological tasks but are strongly inhibited by Zn2+ cations. Some determinants of Zn2+ binding have been elucidated experimentally and in computational studies. However, the results have always been interpreted under the assumption that Zn2+ binds to monomeric HV1 despite evidence that HV1 expresses as a dimer and that the dimer has a higher affinity for zinc than the monomer and experimental data that suggest coordination in the dimer interface. The results of former studies are also controversial, e.g., supporting either one single or two binding sites. Some structural determinants of the binding are still elusive. We performed a series of molecular dynamics simulations to address different structures of the human proton channel, the monomer and two plausible dimer conformations, to compare their respective potential to interact with and bind Zn2+ via the essential histidines. The series consisted of several copies of the system to generate independent trajectories and increase the significance compared to a single simulation. The amount of time simulated totals 29.9 μs for 126 simulations of systems comprising ∼59,000 to ∼187,000 atoms. Our approach confirms the existence of two binding sites in monomeric and dimeric human HV1. The dimer interface is more efficient for attracting and binding Zn2+ via the essential histidines than the monomer or a dimer with the histidines in the periphery. The higher affinity is due to the residues in the dimer interface that create an attractive electrostatic potential funneling the zinc cations toward the binding sites.
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Affiliation(s)
- Christophe Jardin
- Institute of Physiology and Pathophysiology, Klinikum Nuremberg Medical School, Paracelsus Medical University, Nuremberg, Germany
| | - Gustavo Chaves
- Institute of Physiology and Pathophysiology, Klinikum Nuremberg Medical School, Paracelsus Medical University, Nuremberg, Germany
| | - Boris Musset
- Institute of Physiology and Pathophysiology, Klinikum Nuremberg Medical School, Paracelsus Medical University, Nuremberg, Germany.
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48
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Raven JA, Gobler CJ, Hansen PJ. Dynamic CO 2 and pH levels in coastal, estuarine, and inland waters: Theoretical and observed effects on harmful algal blooms. HARMFUL ALGAE 2020; 91:101594. [PMID: 32057340 DOI: 10.1016/j.hal.2019.03.012] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 03/08/2019] [Indexed: 06/10/2023]
Abstract
Rising concentrations of atmospheric CO2 results in higher equilibrium concentrations of dissolved CO2 in natural waters, with corresponding increases in hydrogen ion and bicarbonate concentrations and decreases in hydroxyl ion and carbonate concentrations. Superimposed on these climate change effects is the dynamic nature of carbon cycling in coastal zones, which can lead to seasonal and diel changes in pH and CO2 concentrations that can exceed changes expected for open ocean ecosystems by the end of the century. Among harmful algae, i.e. some species and/or strains of Cyanobacteria, Dinophyceae, Prymnesiophyceae, Bacillariophyceae, and Ulvophyceae, the occurrence of a CO2 concentrating mechanisms (CCMs) is the most frequent mechanism of inorganic carbon acquisition in natural waters in equilibrium with the present atmosphere (400 μmol CO2 mol-1 total gas), with varying phenotypic modification of the CCM. No data on CCMs are available for Raphidophyceae or the brown tide Pelagophyceae. Several HAB species and/or strains respond to increased CO2 concentrations with increases in growth rate and/or cellular toxin content, however, others are unaffected. Beyond the effects of altered C concentrations and speciation on HABs, changes in pH in natural waters are likely to have profound effects on algal physiology. This review outlines the implications of changes in inorganic cycling for HABs in coastal zones, and reviews the knowns and unknowns with regard to how HABs can be expected to ocean acidification. We further point to the large regions of uncertainty with regard to this evolving field.
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Affiliation(s)
- John A Raven
- Division of Plant Sciences, University of Dundee at the James Hutton Institute, Invergowrie, Dundee, DD2 5DA, UK; Climate Change Cluster, University of Technology Sydney, Ultimo, NSW, 2007, Australia; School of Biological Science, University of Western Australia, Crawley, WA, 6009, Australia.
| | - Christopher J Gobler
- School of Marine and Atmospheric Sciences, Stony Brook University, Southampton NY, 11968, USA.
| | - Per Juel Hansen
- University of Copenhagen, Marine Biological Section, Strandpromenaden 5, DK 3000 Helsingør, Denmark
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Bayrhuber M, Maslennikov I, Kwiatkowski W, Sobol A, Wierschem C, Eichmann C, Frey L, Riek R. Nuclear Magnetic Resonance Solution Structure and Functional Behavior of the Human Proton Channel. Biochemistry 2019; 58:4017-4027. [PMID: 31365236 DOI: 10.1021/acs.biochem.9b00471] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The human voltage-gated proton channel [Hv1(1) or VSDO(2)] plays an important role in the human innate immune system. Its structure differs considerably from those of other cation channels. It is built solely of a voltage-sensing domain and thus lacks the central pore domain, which is essential for other cation channels. Here, we determined the solution structure of an N- and C-terminally truncated human Hv1 (Δ-Hv1) in the resting state by nuclear magnetic resonance (NMR) spectroscopy. Δ-Hv1 comprises the typical voltage-sensing antiparallel four-helix bundle (S1-S4) preceded by an amphipathic helix (S0). The solution structure corresponds to an intermediate state between resting and activated forms of voltage-sensing domains. Furthermore, Zn2+-induced closing of proton channel Δ-Hv1 was studied with two-dimensional NMR spectroscopy, which showed that characteristic large scale dynamics of open Δ-Hv1 are absent in the closed state of the channel. Additionally, pH titration studies demonstrated that a higher H+ concentration is required for the protonation of side chains in the Zn2+-induced closed state than in the open state. These observations demonstrate both structural and dynamical changes involved in the process of voltage gating of the Hv1 channel and, in the future, may help to explain the unique properties of unidirectional conductance and the exceptional ion selectivity of the channel.
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Affiliation(s)
- Monika Bayrhuber
- Laboratory of Physical Chemistry , ETH Zürich , Wolfgang-Pauli-Strasse 10 , 8093 Zürich , Switzerland.,Structural Biology Laboratory , Salk Institute , 10010 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Innokentiy Maslennikov
- Structural Biology Laboratory , Salk Institute , 10010 North Torrey Pines Road , La Jolla , California 92037 , United States.,School of Pharmacy , Chapman University , 9401 Jeronimo Road , Irvine , California 92618 , United States
| | - Witek Kwiatkowski
- Laboratory of Physical Chemistry , ETH Zürich , Wolfgang-Pauli-Strasse 10 , 8093 Zürich , Switzerland.,Structural Biology Laboratory , Salk Institute , 10010 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Alexander Sobol
- Laboratory of Physical Chemistry , ETH Zürich , Wolfgang-Pauli-Strasse 10 , 8093 Zürich , Switzerland
| | - Christoph Wierschem
- Laboratory of Physical Chemistry , ETH Zürich , Wolfgang-Pauli-Strasse 10 , 8093 Zürich , Switzerland
| | - Cédric Eichmann
- Laboratory of Physical Chemistry , ETH Zürich , Wolfgang-Pauli-Strasse 10 , 8093 Zürich , Switzerland
| | - Lukas Frey
- Laboratory of Physical Chemistry , ETH Zürich , Wolfgang-Pauli-Strasse 10 , 8093 Zürich , Switzerland
| | - Roland Riek
- Laboratory of Physical Chemistry , ETH Zürich , Wolfgang-Pauli-Strasse 10 , 8093 Zürich , Switzerland.,Structural Biology Laboratory , Salk Institute , 10010 North Torrey Pines Road , La Jolla , California 92037 , United States
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Hydrophobic gasket mutation produces gating pore currents in closed human voltage-gated proton channels. Proc Natl Acad Sci U S A 2019; 116:18951-18961. [PMID: 31462498 PMCID: PMC6754559 DOI: 10.1073/pnas.1905462116] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
A large family of membrane proteins, voltage-gated ion channels, regulate a vast array of physiological functions in essentially all life forms. How these molecules sense membrane potential and respond by creating ionic conduction is incompletely understood. The voltage sensors of these channels contain a “hydrophobic gasket,” a ring of hydrophobic amino acids near the center of the membrane, separating internal and external aqueous solutions. Although voltage-gated proton channels, HV1, resemble voltage-sensing domains of other channels, they differ fundamentally. On depolarization, HV1 conducts protons, whereas other voltage sensors open a physically distinct pore. We identify Val109, Phe150, Val177, and Val178 as the hHV1 hydrophobic gasket. Replacement with less hydrophobic amino acids accelerated channel opening and caused proton-selective leak through closed channels. The hydrophobic gasket (HG), a ring of hydrophobic amino acids in the voltage-sensing domain of most voltage-gated ion channels, forms a constriction between internal and external aqueous vestibules. Cationic Arg or Lys side chains lining the S4 helix move through this “gating pore” when the channel opens. S4 movement may occur during gating of the human voltage-gated proton channel, hHV1, but proton current flows through the same pore in open channels. Here, we replaced putative HG residues with less hydrophobic residues or acidic Asp. Substitution of individuals, pairs, or all 3 HG positions did not impair proton selectivity. Evidently, the HG does not act as a secondary selectivity filter. However, 2 unexpected functions of the HG in HV1 were discovered. Mutating HG residues independently accelerated channel opening and compromised the closed state. Mutants exhibited open–closed gating, but strikingly, at negative voltages where “normal” gating produces a nonconducting closed state, the channel leaked protons. Closed-channel proton current was smaller than open-channel current and was inhibited by 10 μM Zn2+. Extreme hyperpolarization produced a deeper closed state through a weakly voltage-dependent transition. We functionally identify the HG as Val109, Phe150, Val177, and Val178, which play a critical and exclusive role in preventing H+ influx through closed channels. Molecular dynamics simulations revealed enhanced mobility of Arg208 in mutants exhibiting H+ leak. Mutation of HG residues produces gating pore currents reminiscent of several channelopathies.
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