1
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Kammel M, Pinske C, Sawers RG. FocA and its central role in fine-tuning pH homeostasis of enterobacterial formate metabolism. MICROBIOLOGY (READING, ENGLAND) 2022; 168. [PMID: 36197793 DOI: 10.1099/mic.0.001253] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
During enterobacterial mixed-acid fermentation, formate is generated from pyruvate by the glycyl-radical enzyme pyruvate formate-lyase (PflB). In Escherichia coli, especially at low pH, formate is then disproportionated to CO2 and H2 by the cytoplasmically oriented, membrane-associated formate hydrogenlyase (FHL) complex. If electron acceptors are available, however, formate is oxidized by periplasmically oriented, respiratory formate dehydrogenases. Formate translocation across the cytoplasmic membrane is controlled by the formate channel, FocA, a member of the formate-nitrite transporter (FNT) family of homopentameric anion channels. This review highlights recent advances in our understanding of how FocA helps to maintain intracellular formate and pH homeostasis during fermentation. Efflux and influx of formate/formic acid are distinct processes performed by FocA and both are controlled through protein interaction between FocA's N-terminal domain with PflB. Formic acid efflux by FocA helps to maintain cytoplasmic pH balance during exponential-phase growth. Uptake of formate against the electrochemical gradient (inside negative) is energetically and mechanistically challenging for a fermenting bacterium unless coupled with proton/cation symport. Translocation of formate/formic acid into the cytoplasm necessitates an active FHL complex, whose synthesis also depends on formate. Thus, FocA, FHL and PflB function together to govern formate homeostasis. We explain how FocA achieves efflux of formic acid and propose mechanisms for pH-dependent uptake of formate both with and without proton symport. We propose that FocA displays both channel- and transporter-like behaviour. Whether this translocation behaviour is shared by other members of the FNT family is also discussed.
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Affiliation(s)
- Michelle Kammel
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Constanze Pinske
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - R Gary Sawers
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
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2
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Kammel M, Sawers RG. Distinguishing functional from structural roles of conserved pore residues during formate translocation by the FocA anion channel. Microbiologyopen 2022; 11:e1312. [PMID: 36031960 PMCID: PMC9380403 DOI: 10.1002/mbo3.1312] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 08/02/2022] [Accepted: 08/02/2022] [Indexed: 11/10/2022] Open
Abstract
The formate‐specific anion channel FocA of Escherichia coli belongs to the superfamily of homopentameric formate‐nitrite transporters (FNT). Minimally nine amino acid residues are conserved in the formate translocation pore of each protomer of the pentamer, including a histidine (H209) and a threonine (T91), both of which are crucial for bidirectional formate translocation through the pore. Information regarding in vivo functional or structural roles for the other seven conserved residues is limited, or nonexistent. Here, we conducted an amino acid‐exchange analysis of these seven conserved residues. Using an established formate‐responsive lacZ‐based assay to monitor changes in intracellular formate levels and anaerobic growth rate due to the inhibitory formate analog hypophosphite, we identified five of the seven residues analyzed to be important for the structural integrity of the pentamer, in particular, two highly conserved asparagine residues, N213 and N262. The remaining two conserved residues, K156 and N172, were essential for formate/hypophosphite translocation. K156 is located on the periplasmic fringe of the pore and aids the attraction of formate to the channel. Here, we show that this residue is also important for formate efflux from the cytoplasm to the periplasm, suggesting a role in formate release from the pore. N172 could be replaced by alanine with retention of low‐level bidirectional anion translocation function; however, exchange for threonine abolished anion translocation. N172 is, therefore, crucial for bidirectional formate translocation, possibly through its interaction with the conserved pore residue, T91.
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Affiliation(s)
- Michelle Kammel
- Institute for Biology/Microbiology, Martin Luther University Halle-Wittenberg, Halle, Saale, Germany
| | - R Gary Sawers
- Institute for Biology/Microbiology, Martin Luther University Halle-Wittenberg, Halle, Saale, Germany
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3
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Manoj KM, Bazhin NM, Tamagawa H, Jaeken L, Parashar A. The physiological role of complex V in ATP synthesis: Murzyme functioning is viable whereas rotary conformation change model is untenable. J Biomol Struct Dyn 2022; 41:3993-4012. [PMID: 35394896 DOI: 10.1080/07391102.2022.2060307] [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: 10/18/2022]
Abstract
Complex V or FoF1-ATPase is a multimeric protein found in bioenergetic membranes of cells and organelles like mitochondria/chloroplasts. The popular perception on Complex V deems it as a reversible molecular motor, working bi-directionally (breaking or making ATP) via a conformation-change based chemiosmotic rotary ATP synthesis (CRAS) mechanism, driven by proton-gradients or trans-membrane potential (TMP). In continuance of our pursuits against the CRAS model of cellular bioenergetics, herein we demonstrate the validity of the murburn model based in diffusible reactive (oxygen) species (DRS/DROS). Supported by new in silico derived data (that there are ∼12 adenosine nucleotide binding sites on the F1 bulb and not merely 3 sites, as perceived earlier), available structural information, known experimental observations, and thermodynamic/kinetic considerations (that de-solvation of protons from hydronium ions is facile), we deduce that Complex V serves as a physiological chemostat and a murzyme (enzyme working via murburn scheme, employing DRS). That is- Complex V uses ATP (via consumption at ε or proteins of F1 module) as a Michaelis-Menten substrate to serve as a pH-stat by inletting protons via the c-ring of Fo module. Physiologically, Complex V also functions as a murzyme by presenting ADP/Pi (or their reaction intermediates) on the αβ bulb, thereby enabling greater opportunities for DRS/proton-assisted ATP formation. Thus, the murburn paradigm succeeds the CRAS hypothesis for explaining the role of oxygen in mitochondrial physiologies of oxidative phosphorylation, thermogenesis, TMP and homeostasis.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Kelath Murali Manoj
- Biochemistry Department, Satyamjayatu: The Science & Ethics Foundation, Palakkad, Kerala, India
| | - Nikolai Mikhailovich Bazhin
- Environmental Chemistry Department, Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk, Russia
| | | | - Laurent Jaeken
- Industrial Sciences and Technology, Karel de Grote University College, Antwerp University Association, Hoboken, Belgium
| | - Abhinav Parashar
- Biochemistry Department, Satyamjayatu: The Science & Ethics Foundation, Palakkad, Kerala, India
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4
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Wang Y, Xiao E, Wu G, Bai Q, Xu F, Ji X, Li C, Li L, Liu J. The roles of selectivity filters in determining aluminum transport by AtNIP1;2. PLANT SIGNALING & BEHAVIOR 2021; 16:1991686. [PMID: 34709126 PMCID: PMC9208765 DOI: 10.1080/15592324.2021.1991686] [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: 08/25/2021] [Revised: 10/03/2021] [Accepted: 10/06/2021] [Indexed: 05/26/2023]
Abstract
Aquaporins (AQPs) are channel proteins involved in transporting a variety of substrates. It has been proposed that the constriction regions in the central pores of the AQP channels play a crucial role in determining transport substrates and activities of AQPs. Our previous results suggest that AtNIP1;2, a member of the AQP superfamily in Arabidopsis, facilitates aluminum transport across the plasma membrane. However, the functions of the constriction regions in AtNIP1;2-mediated transport activities are unclear. This study reports that residue substitutions of the constriction regions affect AtNIP1;2-mediated aluminum uptake, demonstrating the critical roles of the constriction regions for transport activities. Furthermore, a constriction region that partially or wholly mimics AtNIP5;1, a demonstrated boric-acid transporter, could not render the boric-acid transport activity to AtNIP1;2. Therefore, besides the constriction regions, other structural features are also involved in determining the nature of AtNIP1;2's transport activities.Abbreviations: AIAR: alanine-isoleucine-alanine-arginine; AIGR: alanine-isoleucine-glycine- arginine; AQP: aquaporin; Al-Mal: aluminum-malate; ar/R: aromatic/arginine; AVAR: alanine-valine-alanine-arginine; CK: control; H: helical domain; ICP-MS: inductively coupled plasma mass spectrometry; LA - LE: inter-helical loops A to E; NIP: nodulin 26-like intrinsic protein; NPA: asparagine-proline-alanine; NPG: asparagine-proline- glycine; NPS: asparagine-proline-Serine; NPV: asparagine-proline-valine; ORF: open reading frame; PIP: plasma membrane intrinsic proteins; SIP: small basic intrinsic proteins; TM: transmembrane helices; WIAR: tryptophan-isoleucine-alanine-arginine; WVAR: tryptophan-valine-alanine-arginine; WVGR: tryptophan-valine-glycine- arginine.
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Affiliation(s)
- Yuqi Wang
- Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
| | - Enzong Xiao
- Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
| | - Guorong Wu
- Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
| | - Qing Bai
- Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
| | - Feng Xu
- Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
| | - Xiyue Ji
- Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
| | - Chune Li
- Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
| | - Li Li
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
- Plant Breeding and Genetics Section, School of Integrative Plant Sciences, Cornell University, Ithaca, Ny, USA
| | - Jiping Liu
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
- Plant Breeding and Genetics Section, School of Integrative Plant Sciences, Cornell University, Ithaca, Ny, USA
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5
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Ardalan A, Sowlati-Hashjin S, Uwumarenogie SO, Fish M, Mitchell J, Karttunen M, Smith MD, Jelokhani-Niaraki M. Functional Oligomeric Forms of Uncoupling Protein 2: Strong Evidence for Asymmetry in Protein and Lipid Bilayer Systems. J Phys Chem B 2020; 125:169-183. [PMID: 33373220 DOI: 10.1021/acs.jpcb.0c09422] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Stoichiometry of uncoupling proteins (UCPs) and their coexistence as functional monomeric and associated forms in lipid membranes remain intriguing open questions. In this study, tertiary and quaternary structures of UCP2 were analyzed experimentally and through molecular dynamics (MD) simulations. UCP2 was overexpressed in the inner membrane of Escherichia coli, then purified and reconstituted in lipid vesicles. Structure and proton transport function of UCP2 were characterized by circular dichroism (CD) spectroscopy and fluorescence methods. Findings suggest a tetrameric functional form for UCP2. MD simulations conclude that tetrameric UCP2 is a dimer of dimers, is more stable than its monomeric and dimeric forms, is asymmetrical and induces asymmetry in the membrane's lipid structure, and a biphasic on-off switch between the dimeric units is its possible mode of transport. MD simulations also show that the water density inside the UCP2 monomer is asymmetric, with the cytoplasmic side having a higher water density and a wider radius. In contrast, the structurally comparable adenosine 5'-diphosphate (ADP)/adenosine 5'-triphosphate (ATP) carrier (AAC1) did not form tetramers, implying that tetramerization cannot be generalized to all mitochondrial carriers.
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Affiliation(s)
- Afshan Ardalan
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5
| | - Shahin Sowlati-Hashjin
- Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 3K7.,Center for Advanced Materials and Biomaterials Research, The University of Western Ontario, London, Ontario, Canada N6K 3K7
| | - Stephanie O Uwumarenogie
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5
| | - Michael Fish
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5.,Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5
| | - Joel Mitchell
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5
| | - Mikko Karttunen
- Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 3K7.,Center for Advanced Materials and Biomaterials Research, The University of Western Ontario, London, Ontario, Canada N6K 3K7.,Department of Applied Mathematics, The University of Western Ontario, London, Ontario, Canada N6A 5B7
| | - Matthew D Smith
- Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5
| | - Masoud Jelokhani-Niaraki
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5
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6
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Nielsen BS, Toft-Bertelsen TL, Lolansen SD, Anderson CL, Nielsen MS, Thompson RJ, MacAulay N. Pannexin 1 activation and inhibition is permeant-selective. J Physiol 2020; 598:361-379. [PMID: 31698505 DOI: 10.1113/jp278759] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 11/05/2019] [Indexed: 01/14/2023] Open
Abstract
KEY POINTS The large-pore channel pannexin 1 (Panx1) is expressed in many cell types and can open upon different, yet not fully established, stimuli. Panx1 permeability is often inferred from channel permeability to fluorescent dyes, but it is currently unknown whether dye permeability translates to permeability to other molecules. Cell shrinkage and C-terminal cleavage led to a Panx1 open-state with increased permeability to atomic ions (current), but did not alter ethidium uptake. Panx1 inhibitors affected Panx1-mediated ion conduction differently from ethidium permeability, and inhibitor efficiency towards a given molecule therefore cannot be extrapolated to its effects on the permeability of another. We conclude that ethidium permeability does not reflect equal permeation of other molecules and thus is no measure of general Panx1 activity. ABSTRACT Pannexin 1 (Panx1) is a large-pore membrane channel connecting the extracellular milieu with the cell interior. While several activation regimes activate Panx1 in a variety of cell types, the selective permeability of an open Panx1 channel remains unresolved: does a given activation paradigm increase Panx1's permeability towards all permeants equally and does fluorescent dye flux serve as a proxy for biological permeation through an open channel? To explore permeant-selectivity of Panx1 activation and inhibition, we employed Panx1-expressing Xenopus laevis oocytes and HEK293T cells. We report that different mechanisms of activation of Panx1 differentially affected ethidium and atomic ion permeation. Most notably, C-terminal truncation or cell shrinkage elevated Panx1-mediated ion conductance, but had no effect on ethidium permeability. In contrast, extracellular pH changes predominantly affected ethidium permeability but not ionic conductance. High [K+ ]o did not increase the flux of either of the two permeants. Once open, Panx1 demonstrated preference for anionic permeants, such as Cl- , lactate and glutamate, while not supporting osmotic water flow. Panx1 inhibitors displayed enhanced potency towards Panx1-mediated currents compared to that of ethidium uptake. We conclude that activation or inhibition of Panx1 display permeant-selectivity and that permeation of ethidium does not necessarily reflect an equal permeation of smaller biological molecules and atomic ions.
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Affiliation(s)
- Brian Skriver Nielsen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Trine Lisberg Toft-Bertelsen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Sara Diana Lolansen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Connor L Anderson
- Department of Cell Biology and Anatomy, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
| | - Morten Schak Nielsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Roger J Thompson
- Department of Cell Biology and Anatomy, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
| | - Nanna MacAulay
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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7
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Sánchez-Aparicio JE, Sciortino G, Herrmannsdoerfer DV, Chueca PO, Pedregal JRG, Maréchal JD. GPathFinder: Identification of Ligand-Binding Pathways by a Multi-Objective Genetic Algorithm. Int J Mol Sci 2019; 20:E3155. [PMID: 31261636 PMCID: PMC6651367 DOI: 10.3390/ijms20133155] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Revised: 06/19/2019] [Accepted: 06/21/2019] [Indexed: 12/21/2022] Open
Abstract
Protein-ligand docking is a widely used method to generate solutions for the binding of a small molecule with its target in a short amount of time. However, these methods provide identification of physically sound protein-ligand complexes without a complete view of the binding process dynamics, which has been recognized to be a major discriminant in binding affinity and ligand selectivity. In this paper, a novel piece of open-source software to approach this problem is presented, called GPathFinder. It is built as an extension of the modular GaudiMM platform and is able to simulate ligand diffusion pathways at atomistic level. The method has been benchmarked on a set of 20 systems whose ligand-binding routes were studied by other computational tools or suggested from experimental "snapshots". In all of this set, GPathFinder identifies those channels that were already reported in the literature. Interestingly, the low-energy pathways in some cases indicate novel possible binding routes. To show the usefulness of GPathFinder, the analysis of three case systems is reported. We believe that GPathFinder is a software solution with a good balance between accuracy and computational cost, and represents a step forward in extending protein-ligand docking capacities, with implications in several fields such as drug or enzyme design.
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Affiliation(s)
| | - Giuseppe Sciortino
- Departament de Química, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain
| | | | - Pablo Orenes Chueca
- Departament de Química, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain
| | | | - Jean-Didier Maréchal
- Departament de Química, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain.
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8
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Bernardi M, Marracino P, Ghaani MR, Liberti M, Del Signore F, Burnham CJ, Gárate JA, Apollonio F, English NJ. Human aquaporin 4 gating dynamics under axially oriented electric-field impulses: A non-equilibrium molecular-dynamics study. J Chem Phys 2019; 149:245102. [PMID: 30599740 DOI: 10.1063/1.5044665] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Human aquaporin 4 has been studied using non-equilibrium molecular dynamics simulations in the absence and presence of pulses of external electric fields. The pulses were 100 ns in duration and 0.005-0.015 V/Å in intensity acting along the pores' axes. Water diffusivity and the dipolar response of various residues of interest within the pores have been studied. Results show relatively little change in levels of water permeability per se within aquaporin channels during axially oriented field impulses, although care must be taken with regard to statistical certainty. However, the spatial variation of water permeability vis-à-vis electric-field intensity within the milieu of the channels, as revealed by heterogeneity in diffusivity-map gradients, indicates the possibility of somewhat enhanced diffusivity, owing to several residues being affected substantially by external fields, particularly for HIS 201 and 95 and ILE 93. This has the effect of increasing slightly intra-pore water diffusivity in the "pore-mouths" locale, albeit rendering it more spatially uniform overall vis-à-vis zero-field conditions (via manipulation of the selectivity filter).
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Affiliation(s)
- Mario Bernardi
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy
| | - Paolo Marracino
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy
| | - Mohammad Reza Ghaani
- School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin, D4, Ireland
| | - Micaela Liberti
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy
| | - Federico Del Signore
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy
| | - Christian J Burnham
- School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin, D4, Ireland
| | - José-Antonio Gárate
- Centro Interdisciplinario de neurociencia de Valparaíso, CINV, Universidad de Valparaíso, 05101 Valparaíso, Chile
| | - Francesca Apollonio
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy
| | - Niall J English
- School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin, D4, Ireland
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9
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Trefz M, Keller R, Vogt M, Schneider D. The GlpF residue Trp219 is part of an amino-acid cluster crucial for aquaglyceroporin oligomerization and function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:887-894. [PMID: 29069569 DOI: 10.1016/j.bbamem.2017.10.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 10/10/2017] [Accepted: 10/15/2017] [Indexed: 12/13/2022]
Abstract
The vestibule loop regions of aquaglyceroporins are involved in accumulation of glycerol inside the channel pore. Even though most loop regions do not show high sequence similarity among aquaglyceroporins, loop E is highly conserved in aquaglyceroporins, but not in members of the homologous aquaporins. Specifically, a tryptophan residue is extremely conserved within this loop. We have investigated the role of this residue (Trp219) that deeply protrudes into the protein and potentially interacts with adjacent loops, using the E. coli aqualgyeroporin GlpF as a model. Replacement of Trp219 affects the activity of GlpF and impairs the stability of the tetrameric protein. Furthermore, we have identified an amino acid cluster involving Trp219 that stabilizes the GlpF tetramer. Based on our results we propose that Trp219 is key for formation of a defined vestibule structure, which is crucial for glycerol accumulation as well as for the stability of the active GlpF tetramer.
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Affiliation(s)
- Margareta Trefz
- Johannes Gutenberg University, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Rebecca Keller
- Johannes Gutenberg University, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Miriam Vogt
- Johannes Gutenberg University, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Dirk Schneider
- Johannes Gutenberg University, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany.
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10
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Burnham CJ, English NJ. Electropumping of Water Through Human Aquaporin 4 by Circularly Polarized Electric Fields: Dramatic Enhancement and Control Revealed by Non-Equilibrium Molecular Dynamics. J Phys Chem Lett 2017; 8:4646-4651. [PMID: 28905623 DOI: 10.1021/acs.jpclett.7b02323] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
An extensive suite of nonequilibrium molecular-dynamics (NEMD) simulations have been performed for ∼60 ns of human aquaporin 4 in externally applied circularly polarized (CP) electric fields, applied axially along channels. These external fields were 0.05 V/Å in intensity and 100 GHz in frequency. This has the effect of "electro-pumping" the water through the pores as prototypical biochannels, from conversion of molecules' spin angular momentum to linear momentum in the asymmetric heterogeneous-frictional environment of the pores, thus inducing overall net flow. Water's osmotic permeability was enhanced very substantially (doubled) vis-à-vis the zero-field case. This raises the tantalizing possibility of CP-field-mediated control of water permeability in aquaporins, or other biological (or biomimetic) channels as a potential viable and competitive water-treatment technology.
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Affiliation(s)
- Christian J Burnham
- School of Chemical and Bioprocess Engineering, University College Dublin , Belfield, Dublin 4, Ireland
| | - Niall J English
- School of Chemical and Bioprocess Engineering, University College Dublin , Belfield, Dublin 4, Ireland
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11
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Ni ZX, Cui JM, Zhang NZ, Fu BQ. Structural and evolutionary divergence of aquaporins in parasites (Review). Mol Med Rep 2017; 15:3943-3948. [PMID: 28440467 PMCID: PMC5436202 DOI: 10.3892/mmr.2017.6505] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 02/28/2017] [Indexed: 11/05/2022] Open
Abstract
Aquaporins are ubiquitous proteins that belong to the major intrinsic protein family. Previous studies have indicated that aquaporins are involved in multiple physiological processes in parasites, such as nutrient absorption and end product efflux, and thus, would be promising pharmacological agents in the fight against parasite infection. In the present paper, the authors analyzed the evolutionary relationship of parasitic aquaporins by re‑constructing of a phylogenic tree using neighbor‑joining and maximum likelihood methods. In addition, the authors discussed the variation of the conserved functional sites impacting on the transportation of water molecules. The protein was concluded to be a potential drug target in parasites.
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Affiliation(s)
- Zi-Xin Ni
- College of Veterinary Medicine, China Agricultural University, Beijing 100083, P.R. China
| | - Jian-Min Cui
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu 730046, P.R. China
| | - Nian-Zhang Zhang
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu 730046, P.R. China
| | - Bao-Quan Fu
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu 730046, P.R. China
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12
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Nielsen BS, Hansen DB, Ransom BR, Nielsen MS, MacAulay N. Connexin Hemichannels in Astrocytes: An Assessment of Controversies Regarding Their Functional Characteristics. Neurochem Res 2017; 42:2537-2550. [DOI: 10.1007/s11064-017-2243-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 03/17/2017] [Accepted: 03/17/2017] [Indexed: 12/19/2022]
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13
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Padhi S, Priyakumar UD. Microsecond simulation of human aquaporin 2 reveals structural determinants of water permeability and selectivity. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:10-16. [DOI: 10.1016/j.bbamem.2016.10.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 10/19/2016] [Accepted: 10/21/2016] [Indexed: 02/06/2023]
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14
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Wang S, Ing C, Emami S, Jiang Y, Liang H, Pomès R, Brown LS, Ladizhansky V. Structure and Dynamics of Extracellular Loops in Human Aquaporin-1 from Solid-State NMR and Molecular Dynamics. J Phys Chem B 2016; 120:9887-902. [DOI: 10.1021/acs.jpcb.6b06731] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Shenlin Wang
- Department
of Physics, University of Guelph, Guelph, ON, Canada N1G 2W1
| | - Christopher Ing
- Molecular
Structure and Function, Hospital for Sick Children, Toronto, ON, Canada M5G 1X8
- Department
of Biochemistry, University of Toronto, Toronto, ON, Canada M5S 1A8
| | - Sanaz Emami
- Department
of Physics, University of Guelph, Guelph, ON, Canada N1G 2W1
- Biophysics
Interdepartmental Group, University of Guelph, Guelph, ON, Canada N1G 2W1
| | - Yunjiang Jiang
- Department
of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, United States
| | - Hongjun Liang
- Department
of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, United States
| | - Régis Pomès
- Molecular
Structure and Function, Hospital for Sick Children, Toronto, ON, Canada M5G 1X8
- Department
of Biochemistry, University of Toronto, Toronto, ON, Canada M5S 1A8
| | - Leonid S. Brown
- Department
of Physics, University of Guelph, Guelph, ON, Canada N1G 2W1
- Biophysics
Interdepartmental Group, University of Guelph, Guelph, ON, Canada N1G 2W1
| | - Vladimir Ladizhansky
- Department
of Physics, University of Guelph, Guelph, ON, Canada N1G 2W1
- Biophysics
Interdepartmental Group, University of Guelph, Guelph, ON, Canada N1G 2W1
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15
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English NJ, Garate JA. Near-microsecond human aquaporin 4 gating dynamics in static and alternating external electric fields: Non-equilibrium molecular dynamics. J Chem Phys 2016; 145:085102. [DOI: 10.1063/1.4961072] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Affiliation(s)
- Niall J. English
- School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin 4, Ireland
| | - José-A. Garate
- Computational Biology Laboratory, Life Sciences Foundation, Santiago, Chile
- Centro Interdisciplinario de neurociencia de Valparaiso, Universidad de Valparaiso, Valparaiso, Chile
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16
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Marracino P, Liberti M, Trapani E, Burnham CJ, Avena M, Garate JA, Apollonio F, English NJ. Human Aquaporin 4 Gating Dynamics under Perpendicularly-Oriented Electric-Field Impulses: A Molecular Dynamics Study. Int J Mol Sci 2016; 17:E1133. [PMID: 27428954 PMCID: PMC4964506 DOI: 10.3390/ijms17071133] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Revised: 07/01/2016] [Accepted: 07/04/2016] [Indexed: 12/25/2022] Open
Abstract
Human aquaporin 4 has been studied using molecular dynamics (MD) simulations in the absence and presence of pulses of external static electric fields. The pulses were 10 ns in duration and 0.012-0.065 V/Å in intensity acting along both directions perpendicular to the pores. Water permeability and the dipolar response of all residues of interest (including the selectivity filter) within the pores have been studied. Results showed decreased levels of water osmotic permeability within aquaporin channels during orthogonally-oriented field impulses, although care must be taken with regard to statistical certainty. This can be explained observing enhanced "dipolar flipping" of certain key residues, especially serine 211, histidine 201, arginine 216, histidine 95 and cysteine 178. These residues are placed at the extracellular end of the pore (serine 211, histidine 201, and arginine 216) and at the cytoplasm end (histidine 95 and cysteine 178), with the key role in gating mechanism, hence influencing water permeability.
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Affiliation(s)
- Paolo Marracino
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy.
| | - Micaela Liberti
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy.
| | - Erika Trapani
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy.
| | - Christian J Burnham
- School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, D4 Dublin, Ireland.
| | - Massimiliano Avena
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy.
| | - José-Antonio Garate
- Computational Biology Laboratory, Life Sciences Foundation, 7750000 Santiago, Chile.
- Centro Interdisciplinario de neurociencia de Valparaiso, Universidad de Valparaiso, 05101 Valparaiso, Chile.
| | - Francesca Apollonio
- Department of Information Engineering, Electronics and Telecommunications, La Sapienza University, 00184 Rome, Italy.
| | - Niall J English
- School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, D4 Dublin, Ireland.
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17
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He Z, Yan H, Chen Y, Shen H, Xu W, Zhang H, Shi L, Zhu YG, Ma M. An aquaporin PvTIP4;1 from Pteris vittata may mediate arsenite uptake. THE NEW PHYTOLOGIST 2016; 209:746-61. [PMID: 26372374 DOI: 10.1111/nph.13637] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Accepted: 08/05/2015] [Indexed: 05/07/2023]
Abstract
The fern Pteris vittata is an arsenic hyperaccumulator. The genes involved in arsenite (As(III)) transport are not yet clear. Here, we describe the isolation and characterization of a new P. vittata aquaporin gene, PvTIP4;1, which may mediate As(III) uptake. PvTIP4;1 was identified from yeast functional complement cDNA library of P. vittata. Arsenic toxicity and accumulating activities of PvTIP4;1 were analyzed in Saccharomyces cerevisiae and Arabidopsis. Subcellular localization of PvTIP4;1-GFP fusion protein in P. vittata protoplast and callus was conducted. The tissue expression of PvTIP4;1 was investigated by quantitative real-time PCR. Site-directed mutagenesis of the PvTIP4;1 aromatic/arginine (Ar/R) domain was studied. Heterologous expression in yeast demonstrates that PvTIP4;1 was able to facilitate As(III) diffusion. Transgenic Arabidopsis showed that PvTIP4;1 increases arsenic accumulation and induces arsenic sensitivity. Images and FM4-64 staining suggest that PvTIP4;1 localizes to the plasma membrane in P. vittata cells. A tissue location study shows that PvTIP4;1 transcripts are mainly expressed in roots. Site-directed mutation in yeast further proved that the cysteine at the LE1 position of PvTIP4;1 Ar/R domain is a functional site. PvTIP4;1 is a new represented tonoplast intrinsic protein (TIP) aquaporin from P. vittata and the function and location results imply that PvTIP4;1 may be involved in As(III) uptake.
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Affiliation(s)
- Zhenyan He
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
| | - Huili Yan
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yanshan Chen
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Hongling Shen
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Wenxiu Xu
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
| | - Haiyan Zhang
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
| | - Lei Shi
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
| | - Yong-Guan Zhu
- Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China
| | - Mi Ma
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
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18
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Hansen DB, Ye ZC, Calloe K, Braunstein TH, Hofgaard JP, Ransom BR, Nielsen MS, MacAulay N. Activation, permeability, and inhibition of astrocytic and neuronal large pore (hemi)channels. J Biol Chem 2014; 289:26058-26073. [PMID: 25086040 DOI: 10.1074/jbc.m114.582155] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Astrocytes and neurons express several large pore (hemi)channels that may open in response to various stimuli, allowing fluorescent dyes, ions, and cytoplasmic molecules such as ATP and glutamate to permeate. Several of these large pore (hemi)channels have similar characteristics with regard to activation, permeability, and inhibitor sensitivity. Consequently, their behaviors and roles in astrocytic and neuronal (patho)physiology remain undefined. We took advantage of the Xenopus laevis expression system to determine the individual characteristics of several large pore channels in isolation. Expression of connexins Cx26, Cx30, Cx36, or Cx43, the pannexins Px1 or Px2, or the purinergic receptor P2X7 yielded functional (hemi)channels with isoform-specific characteristics. Connexin hemichannels had distinct sensitivity to alterations of extracellular Ca(2+) and their permeability to dyes and small atomic ions (conductance) were not proportional. Px1 and Px2 exhibited conductance at positive membrane potentials, but only Px1 displayed detectable fluorescent dye uptake. P2X7, in the absence of Px1, was permeable to fluorescent dyes in an agonist-dependent manner. The large pore channels displayed overlapping sensitivity to the inhibitors Brilliant Blue, gadolinium, and carbenoxolone. These results demonstrated isoform-specific characteristics among the large pore membrane channels; an open (hemi)channel is not a nonselective channel. With these isoform-specific properties in mind, we characterized the divalent cation-sensitive permeation pathway in primary cultured astrocytes. We observed no activation of membrane conductance or Cx43-mediated dye uptake in astrocytes nor in Cx43-expressing C6 cells. Our data underscore that although Cx43-mediated transport is observed in overexpressing cell systems, such transport may not be detectable in native cells under comparable experimental conditions.
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Affiliation(s)
- Daniel Bloch Hansen
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Zu-Cheng Ye
- Department of Neurology, University of Washington, Seattle, Washington 98195
| | - Kirstine Calloe
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg, Denmark, and
| | - Thomas Hartig Braunstein
- Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Johannes Pauli Hofgaard
- Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Bruce R Ransom
- Department of Neurology, University of Washington, Seattle, Washington 98195
| | - Morten Schak Nielsen
- Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Nanna MacAulay
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark,.
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19
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Hansen DB, Braunstein TH, Nielsen MS, MacAulay N. Distinct permeation profiles of the connexin 30 and 43 hemichannels. FEBS Lett 2014; 588:1446-57. [PMID: 24503060 DOI: 10.1016/j.febslet.2014.01.036] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 01/23/2014] [Accepted: 01/24/2014] [Indexed: 01/10/2023]
Abstract
Connexin 43 (Cx43) hemichannels may form open channels in the plasma membrane when exposed to specific stimuli, e.g. reduced extracellular concentration of divalent cations, and allow passage of fluorescent molecules and presumably a range of smaller physiologically relevant molecules. However, the permeability profile of Cx43 hemichannels remains unresolved. Exposure of Cx43-expressing Xenopus laevis oocytes to divalent cation free solution induced a gadolinium-sensitive uptake of the fluorescent dye ethidium. In spite thereof, a range of biological molecules smaller than ethidium, such as glutamate, lactate, and glucose, did not permeate the pore whereas ATP did. In contrast, permeability of glutamate, glucose and ATP was observed in oocytes expressing Cx30. Exposure to divalent cation free solutions induced a robust membrane conductance in Cx30-expressing oocytes but none in Cx43-expressing oocytes. C-terminally truncated Cx43 (M257) displayed increased dye uptake and, unlike wild type Cx43 channels, conducted current. Neither Cx30 nor Cx43 acted as water channels in their hemichannel configuration. Our results demonstrate that connexin hemichannels have isoform-specific permeability profiles and that dye uptake cannot be equaled to permeability of smaller physiologically relevant molecules in given settings.
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Affiliation(s)
- Daniel Bloch Hansen
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Thomas Hartig Braunstein
- Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Morten Schak Nielsen
- Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Nanna MacAulay
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
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20
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Reale R, English NJ, Garate JA, Marracino P, Liberti M, Apollonio F. Human aquaporin 4 gating dynamics under and after nanosecond-scale static and alternating electric-field impulses: A molecular dynamics study of field effects and relaxation. J Chem Phys 2013; 139:205101. [DOI: 10.1063/1.4832383] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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21
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Maffeo C, Bhattacharya S, Yoo J, Wells D, Aksimentiev A. Modeling and simulation of ion channels. Chem Rev 2012; 112:6250-84. [PMID: 23035940 PMCID: PMC3633640 DOI: 10.1021/cr3002609] [Citation(s) in RCA: 148] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Christopher Maffeo
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Swati Bhattacharya
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Jejoong Yoo
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - David Wells
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Aleksei Aksimentiev
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
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22
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Boussac A, Ishida N, Sugiura M, Rappaport F. Probing the role of chloride in Photosystem II from Thermosynechococcus elongatus by exchanging chloride for iodide. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:802-10. [DOI: 10.1016/j.bbabio.2012.02.031] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Revised: 02/21/2012] [Accepted: 02/24/2012] [Indexed: 11/29/2022]
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23
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Araya-Secchi R, Garate JA, Holmes DS, Perez-Acle T. Molecular dynamics study of the archaeal aquaporin AqpM. BMC Genomics 2011; 12 Suppl 4:S8. [PMID: 22369250 PMCID: PMC3287591 DOI: 10.1186/1471-2164-12-s4-s8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Background Aquaporins are a large family of transmembrane channel proteins that are present throughout all domains of life and are implicated in human disorders. These channels, allow the passive but selective movement of water and other small neutral solutes across cell membranes. Aquaporins have been classified into two sub-families: i) strict aquaporins that only allow the passage of water and ii) the less selective aquaglyceroporins that transport water and other neutral solutes, such as glycerol, CO2 or urea. Recently, the identification and characterization of a number of archaeal and bacterial aquaporins suggested the existence of a third sub-family; one that is neither a strict aquaporin nor an aquaglyceroporin. The function and phylogeny of this third family is still a matter of debate. Results Twenty nanosecond molecular dynamics (MD) simulation of a fully hydrated tetramer of AqpM embedded in a lipid bilayer permitted predictions to be made of key biophysical parameters including: single channel osmotic permeability constant (pf), single channel diffusive permeability constant (pd), channel radius, potential water occupancy of the channel and water orientation inside the pore. These properties were compared with those of well characterized representatives of the two main aquaporin sub-families. Results show that changes in the amino acid composition of the aromatic/arginine region affect the size and polarity of the selectivity filter (SF) and could help explain the difference in water permeability between aquaporins. In addition, MD simulation results suggest that AqpM combines characteristics of strict aquaporins, such as the narrow SF and channel radius, with those of aquaglyceroporins, such as a more hydrophobic and less polar SF. Conclusions MD simulations of AqpM extend previous evidence that this archaeal aquaporin exhibits hybrid features intermediate between the two known aquaporin sub-families, supporting the idea that it may constitute a member of a novel class of aquaporins.
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Affiliation(s)
- Raul Araya-Secchi
- Computational Biology Laboratory, Centro de Modelamiento Matematico, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Santiago, Chile.
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24
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Azad AK, Yoshikawa N, Ishikawa T, Sawa Y, Shibata H. Substitution of a single amino acid residue in the aromatic/arginine selectivity filter alters the transport profiles of tonoplast aquaporin homologs. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1-11. [PMID: 21963407 DOI: 10.1016/j.bbamem.2011.09.014] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 09/12/2011] [Accepted: 09/13/2011] [Indexed: 11/30/2022]
Abstract
Aquaporins are integral membrane proteins that facilitate the transport of water and some small solutes across cellular membranes. X-ray crystallography of aquaporins indicates that four amino acids constitute an aromatic/arginine (ar/R) pore constriction known as the selectivity filter. On the basis of these four amino acids, tonoplast aquaporins called tonoplast intrinsic proteins (TIPs) are divided into three groups in Arabidopsis. Herein, we describe the characterization of two group I TIP1s (TgTIP1;1 and TgTIP1;2) from tulip (Tulipa gesneriana). TgTIP1;1 and TgTIP1;2 have a novel isoleucine in loop E (LE2 position) of the ar/R filter; the residue at LE2 is a valine in all group I TIPs from model plants. The homologs showed mercury-sensitive water channel activity in a fast kinetics swelling assay upon heterologous expression in Pichia pastoris. Heterologous expression of both homologs promoted the growth of P. pastoris on ammonium or urea as sole sources of nitrogen and decreased growth and survival in the presence of H(2)O(2). TgTIP1;1- and TgTIP1;2-mediated H(2)O(2) conductance was demonstrated further by a fluorescence assay. Substitutions in the ar/R selectivity filter of TgTIP1;1 showed that mutants that mimicked the ar/R constriction of group I TIPs could conduct the same substrates that were transported by wild-type TgTIP1;1. In contrast, mutants that mimicked group II TIPs showed no evidence of urea or H(2)O(2) conductance. These results suggest that the amino acid residue at LE2 position is critical for the transport selectivity of the TIP homologs and group I TIPs might have a broader spectrum of substrate selectivity than group II TIPs.
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Affiliation(s)
- Abul Kalam Azad
- Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan.
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25
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Garate JA, English NJ, MacElroy JMD. Human aquaporin 4 gating dynamics in dc and ac electric fields: A molecular dynamics study. J Chem Phys 2011; 134:055110. [DOI: 10.1063/1.3529428] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
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26
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Azad AK, Sato R, Ohtani K, Sawa Y, Ishikawa T, Shibata H. Functional characterization and hyperosmotic regulation of aquaporin in Synechocystis sp. PCC 6803. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2011; 180:375-382. [PMID: 21421383 DOI: 10.1016/j.plantsci.2010.10.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2010] [Revised: 09/17/2010] [Accepted: 10/19/2010] [Indexed: 05/30/2023]
Abstract
The genome of the cyanobacterium Synechocystis sp. PCC 6803 (hereafter, Synechocystis) contains an aqpZ gene (slr2057) which encodes an aquaporin (SsAqpZ), a membrane channel protein that might play a role in osmotic water transport and therefore the growth of Synechocystis. Structural characterization of SsAqpZ by protein sequence analysis and homology modelling revealed that it was more similar to bacterial aquaporin Z than the glycerol facilitator. To understand the functional role of SsAqpZ, the aqpZ knockout (KO) and myc-tagged aqpZ knockin (KI) Synechocystis were constructed. Water channel activity assays showed that SsAqpZ facilitated water transportation. SsAqpZ-mediated changes in cell volume were observed in wild-type (WT) and KI Synechocystis. Expression of SsAqpZ in KI Synechocystis was induced by extracellular hyperosmolarity. In the absence of hyperosmolarity, WT, KO and KI Synechocystis showed the same pattern of growth and no morphological or phenotypical perturbations. Under hyperosmotic condition, while the WT and also KI cells maintained a similar growth rate throughout the entire exponential phase, KO cells grew significantly slower. These results indicate that SsAqpZ has water channel activity and is involved in the adaptation and maintenance of growth of Synechocystis in a hyperosmotic environment.
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Affiliation(s)
- Abul Kalam Azad
- Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan.
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27
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Hernández-Cobos J, Vargas MC, Ramírez-Solís A, Ortega-Blake I. Aqueous solvation of As(OH)3: A Monte Carlo study with flexible polarizable classical interaction potentials. J Chem Phys 2010; 133:114501. [DOI: 10.1063/1.3483619] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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28
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Nielsen CH. Major intrinsic proteins in biomimetic membranes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 679:127-42. [PMID: 20666229 DOI: 10.1007/978-1-4419-6315-4_10] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Biological membranes define the structural and functional boundaries in living cells and their organelles. The integrity of the cell depends on its ability to separate inside from outside and yet at the same time allow massive transport of matter in and out the cell. Nature has elegantly met this challenge by developing membranes in the form of lipid bilayers in which specialized transport proteins are incorporated. This raises the question: is it possible to mimic biological membranes and create a membrane based sensor and/or separation device? In the development of a biomimetic sensor/separation technology, a unique class of membrane transport proteins is especially interesting-the major intrinsic proteins (MIPs). Generally, MIPs conduct water molecules and selected solutes in and out of the cell while preventing the passage of other solutes, a property critical for the conservation of the cells internal pH and salt concentration. Also known as water channels or aquaporins they are highly efficient membrane pore proteins some of which are capable of transporting water at very high rates up to 10(9) molecules per second. Some MIPs transport other small, uncharged solutes, such as glycerol and other permeants such as carbon dioxide, nitric oxide, ammonia, hydrogen peroxide and the metalloids antimonite, arsenite, silicic and boric acid depending on the effective restriction mechanism of the protein. The flux properties of MIPs thus lead to the question ifMIPs can be used in separation devices or as sensor devices based on, e.g., the selective permeation of metalloids. In principle a MIP based membrane sensor/separation device requires the supporting biomimetic matrix to be virtually impermeable to anything but water or the solute in question. In practice, however, a biomimetic support matrix will generally have finite permeabilities to both electrolytes and non-electrolytes. The feasibility of a biomimetic MIP device thus depends on the relative transport contribution from both protein and biomimetic support matrix. Also the biomimetic matrix must be encapsulated in order to protect it and make it sufficiently stable in a final application. Here, I specifically discuss the feasibility of developing osmotic biomimetic MIP membranes, but the technical issues are of general concern in the design ofbiomimetic membranes capable of supporting selective transmembrane fluxes.
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Affiliation(s)
- Claus Hélix Nielsen
- Quantrum Protein Center, Department of Physics, Technical University of Denmark, DK-2800 Lyngby.
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29
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Nielsen CH. Biomimetic membranes for sensor and separation applications. Anal Bioanal Chem 2009; 395:697-718. [DOI: 10.1007/s00216-009-2960-0] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2009] [Revised: 07/02/2009] [Accepted: 07/07/2009] [Indexed: 01/04/2023]
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30
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Abstract
Channel-forming proteins are found in a number of viral genomes. In some cases, their role in the viral life cycle is well understood, in some cases it needs still to be elucidated. A common theme is that their mode of action involves a change of electrochemical or proton gradient across the lipid membrane which modulates the viral or cellular activity. Blocking these proteins can be a suitable therapeutic strategy as for some viruses this may be "lethal." Besides the many biological relevant questions still to be answered, there are also many open questions concerning the biophysical side as well as structural information and the mechanism of function on a molecular level. The immanent biophysical issues are addressed and the work in the field is summarized.
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Les aquaporines présentes dans le rein. Nephrol Ther 2008; 4:562-7. [DOI: 10.1016/j.nephro.2008.03.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2007] [Revised: 03/28/2008] [Accepted: 03/29/2008] [Indexed: 11/15/2022]
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Invertebrate aquaporins: a review. J Comp Physiol B 2008; 178:935-55. [DOI: 10.1007/s00360-008-0288-2] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Revised: 06/03/2008] [Accepted: 06/10/2008] [Indexed: 10/25/2022]
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Bellemère G, Von Stetten O, Oddos T. Retinoic acid increases aquaporin 3 expression in normal human skin. J Invest Dermatol 2008; 128:542-8. [PMID: 17943189 DOI: 10.1038/sj.jid.5701047] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We have investigated the effects of all-trans retinoic acid (ATRA) on aquaporin 3 (AQP3) expression and function both in vitro and ex vivo. ATRA treatment provoked a rapid accumulation of AQP3 transcripts in cultured normal human epidermal keratinocytes (NHEK). This increase was still observed 24 hours after application of ATRA. The induction of AQP3 gene was accompanied by an augmentation of immunoreactivity. Using a selective agonist, we demonstrated that the effect of ATRA was predominantly mediated by retinoic acid receptor subtype gamma (RARgamma). Incubation of NHEK in ATRA for 24, 48, and 72 hours stimulated glycerol influx, suggesting that the increase in AQP3 gene and protein expression was followed by an enhancement of biological activity. Topical application of ATRA for 24 hours on skin explants induced significant epidermal expression of AQP3 and strong immunoreactivity in the epidermal basal layers. Collectively, the present results show that ATRA increased AQP3 expression and enhanced biological activity in human skin.
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Affiliation(s)
- Gaelle Bellemère
- In vitro Pharmaco-toxicology Laboratory, Johnson & Johnson Consumer France SAS, Campus de Maigremont, Val de Reuil, France.
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Liénard D, Durambur G, Kiefer-Meyer MC, Nogué F, Menu-Bouaouiche L, Charlot F, Gomord V, Lassalles JP. Water transport by aquaporins in the extant plant Physcomitrella patens. PLANT PHYSIOLOGY 2008; 146:1207-18. [PMID: 18184735 PMCID: PMC2259052 DOI: 10.1104/pp.107.111351] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2007] [Accepted: 12/20/2007] [Indexed: 05/19/2023]
Abstract
Although aquaporins (AQPs) have been shown to increase membrane water permeability in many cell types, the physiological role of this increase was not always obvious. In this report, we provide evidence that in the leafy stage of development (gametophore) of the moss Physcomitrella patens, AQPs help to replenish more rapidly the cell water that is lost by transpiration, at least if some water is in the direct vicinity of the moss plant. Three AQP genes were cloned in P. patens: PIP2;1, PIP2;2, and PIP2;3. The water permeability of the membrane was measured in protoplasts from leaves and protonema. A significant decrease was measured in protoplasts from leaves and protonema of PIP2;1 or PIP2;2 knockouts but not the PIP2;3 knockout. No phenotype was observed when knockout plants were grown in closed petri dishes with ample water supply. Gametophores isolated from the wild type and the pip2;3 mutant were not sensitive to moderate water stress, but pip2;1 or pip2;2 gametophores expressed a water stress phenotype. The knockout mutant leaves were more bent and twisted, apparently suffering from an important loss of cellular water. We propose a model to explain how the AQPs PIP2;1 and PIP2;2 delay leaf dessication in a drying atmosphere. We suggest that in ancestral land plants, some 400 million years ago, APQs were already used to facilitate the absorption of water.
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Affiliation(s)
- David Liénard
- Université de Rouen, CNRS UMR 6037, Institut Fédératif de Recherches Multidisciplinaires sur les Peptides, Faculté des Sciences Bât. Ext. Biologie, Mont-Saint-Aignan Cedex, France
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Homology modeling of major intrinsic proteins in rice, maize and Arabidopsis: comparative analysis of transmembrane helix association and aromatic/arginine selectivity filters. BMC STRUCTURAL BIOLOGY 2007; 7:27. [PMID: 17445256 PMCID: PMC1866351 DOI: 10.1186/1472-6807-7-27] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2006] [Accepted: 04/19/2007] [Indexed: 11/12/2022]
Abstract
Background The major intrinsic proteins (MIPs) facilitate the transport of water and neutral solutes across the lipid bilayers. Plant MIPs are believed to be important in cell division and expansion and in water transport properties in response to environmental conditions. More than 30 MIP sequences have been identified in Arabidopsis thaliana, maize and rice. Plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), Nod26-like intrinsic protein (NIPs) and small and basic intrinsic proteins (SIPs) are subfamilies of plant MIPs. Despite sequence diversity, all the experimentally determined structures belonging to the MIP superfamily have the same "hour-glass" fold. Results We have structurally characterized 39 rice and 31 maize MIPs and compared them with that of Arabidopsis. Homology models of 105 MIPs from all three plant species were built. Structure-based sequence alignments were generated and the residues in the helix-helix interfaces were analyzed. Small residues (Gly/Ala/Ser/Thr) are found to be highly conserved as a group in the helix-helix interface of MIP structures. Individual families sometimes prefer one or another of the residues from this group. The narrow aromatic/arginine (ar/R) selectivity filter in MIPs has been shown to provide an important constriction for solute permeability. Ar/R regions were analyzed and compared between the three plant species. Seventeen TIP, NIP and SIP members from rice and maize have ar/R signatures that are not found in Arabidopsis. A subgroup of rice and maize NIPs has small residues in three of the four positions in the ar/R tetrad, resulting in a wider constriction. These MIP members could transport larger solute molecules. Conclusion Small residues are group-conserved in the helix-helix interface of MIP structures and they seem to be important for close helix-helix interactions. Such conservation might help to preserve the hour-glass fold in MIP structures. Analysis and comparison of ar/R selectivity filters suggest that rice and maize MIPs could transport more diverse solutes than Arabidopsis MIPs. Thus the MIP members show conservation in helix-helix interfaces and diversity in aromatic/arginine selectivity filters. The former is related to structural stability and the later can be linked to functional diversity.
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Starkenburg SR, Chain PSG, Sayavedra-Soto LA, Hauser L, Land ML, Larimer FW, Malfatti SA, Klotz MG, Bottomley PJ, Arp DJ, Hickey WJ. Genome sequence of the chemolithoautotrophic nitrite-oxidizing bacterium Nitrobacter winogradskyi Nb-255. Appl Environ Microbiol 2006; 72:2050-63. [PMID: 16517654 PMCID: PMC1393235 DOI: 10.1128/aem.72.3.2050-2063.2006] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The alphaproteobacterium Nitrobacter winogradskyi (ATCC 25391) is a gram-negative facultative chemolithoautotroph capable of extracting energy from the oxidation of nitrite to nitrate. Sequencing and analysis of its genome revealed a single circular chromosome of 3,402,093 bp encoding 3,143 predicted proteins. There were extensive similarities to genes in two alphaproteobacteria, Bradyrhizobium japonicum USDA110 (1,300 genes) and Rhodopseudomonas palustris CGA009 CG (815 genes). Genes encoding pathways for known modes of chemolithotrophic and chemoorganotrophic growth were identified. Genes encoding multiple enzymes involved in anapleurotic reactions centered on C2 to C4 metabolism, including a glyoxylate bypass, were annotated. The inability of N. winogradskyi to grow on C6 molecules is consistent with the genome sequence, which lacks genes for complete Embden-Meyerhof and Entner-Doudoroff pathways, and active uptake of sugars. Two gene copies of the nitrite oxidoreductase, type I ribulose-1,5-bisphosphate carboxylase/oxygenase, cytochrome c oxidase, and gene homologs encoding an aerobic-type carbon monoxide dehydrogenase were present. Similarity of nitrite oxidoreductases to respiratory nitrate reductases was confirmed. Approximately 10% of the N. winogradskyi genome codes for genes involved in transport and secretion, including the presence of transporters for various organic-nitrogen molecules. The N. winogradskyi genome provides new insight into the phylogenetic identity and physiological capabilities of nitrite-oxidizing bacteria. The genome will serve as a model to study the cellular and molecular processes that control nitrite oxidation and its interaction with other nitrogen-cycling processes.
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Abstract
Aquaporins facilitate water permeation across biological membranes. Additionally, glycerol and other small neutral solutes are permeated by related aquaglyceroporins. The role of aquaporins in gas permeation has been a long-standing and controversially discussed issue. We present an extensive set of atomistic molecular dynamics simulations that address the question of CO(2) permeation through human aquaporin-1. Free energy profiles derived from the simulations display a barrier of approximately 23 kJ/mol in the aromatic/arginine constriction region of the water pore, whereas a barrier of approximately 4 kJ/mol was observed for a palmitoyloleoylphosphatidylethanolamine lipid bilayer membrane. The results indicate that significant aquaporin-1-mediated CO(2) permeation is to be expected only in membranes with a low intrinsic CO(2) permeability.
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Affiliation(s)
- Jochen S Hub
- Computational Biomolecular Dynamics Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
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Wallace IS, Roberts DM. Distinct transport selectivity of two structural subclasses of the nodulin-like intrinsic protein family of plant aquaglyceroporin channels. Biochemistry 2006; 44:16826-34. [PMID: 16363796 DOI: 10.1021/bi0511888] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Major intrinsic proteins (MIPs) are a diverse class of integral membrane proteins that facilitate the transport of water and some small solutes across cellular membranes. X-ray structures of MIPs indicate that a tetrad of residues (the ar/R region) form a narrow pore constriction that constitutes the selectivity filter. In comparison with mammalian and microbial species, plants have a greater number and diversity of MIPs with greater than 30 genes encoding four phylogenetic subfamilies with eight different classes of ar/R sequences. The nodulin 26-like intrinsic protein (NIP) subfamily in Arabidopsis can be subdivided into two ar/R subgroups: the NIP subgroup I, which resembles the archetype of the family, soybean nodulin 26, and the NIP subgroup II, which is represented by the Arabidopsis protein AtNIP6;1. These two NIPs differ principally by the substitution of a conserved alanine (NIP subgroup II) for a conserved tryptophan (NIP subgroup I) in the helix 2 position (H2) of the ar/R filter. A comparison of the water and solute tranport properties of the two proteins was performed by expression in Xenopus laevis oocytes. Nodulin 26 is an aquaglyceroporin with a modest osmotic water permeability (P(f)) and the ability to transport uncharged solutes such as glycerol and formamide. In constrast, AtNIP6;1 showed no measurable water permeability but transported glycerol, formamide, as well as larger solutes that were impermeable to nodulin 26. By site-directed mutagenesis, we show that the H2 position is the crucial determinant that confers these transport behaviors. A comparison of the NIPs and tonoplast-intrinsic proteins (TIP) shows that the H2 residue can predict the transport profile for water and glycerol with histidine found in TIP-like aquaporins, tryptophan found in aquaglyceroporins (NIP I), and alanine found in water-impermeable glyceroporins (AtNIP6;1).
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Affiliation(s)
- Ian S Wallace
- Department of Biochemistry and Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee 37996-0840, USA
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Golovko MY, Hovda JT, Cai ZJ, Craigen WJ, Murphy EJ. Tissue-dependent alterations in lipid mass in mice lacking glycerol kinase. Lipids 2005; 40:287-93. [PMID: 15957255 DOI: 10.1007/s11745-005-1384-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Glycerol kinase (ATP:glycerol-3-phosphotransferase, EC 2.7.1.30, glycerokinase) (Gyk) has a central role in plasma glycerol extraction and utilization by tissues for lipid biosynthesis. Gyk deficiency causes various phenotypic changes ranging from asymptomatic hyperglycerolemia to a severe metabolic disorder with growth and psychomotor retardation. To better understand the potential role of Gyk in tissue lipid metabolism, we determined phospholipid (PL), cholesterol (Chol), and triacylglycerol (TG) mass in a number of tissues from mice lacking Gyk. We report a tissue-dependent response to Gyk gene deletion. Tissues with elevated total PL mass (brain, kidney, muscle) were characterized by the increased mass of ethanolamine glycerophospholipids (EtnGpl), choline glycerophospholipids, and phosphatidylserine (PtdSer). In heart, lipid changes were characterized by a reduction in total PL, including decreased EtnGpl, phosphatidylinositol, and PtdSer mass and decreased TG and FFA mass. In parallel with tissue PL alterations, tissue Chol was also changed, maintaining a normal Chol/PL ratio. Under conditions of Gyk deficiency, we speculate that glycerol-3-phosphate and lipid production is maintained via alternative biosynthesis, including glycolysis, glyceroneogenesis, or by direct acylation of glycerol in brain, muscle, kidney, and liver, but not in heart.
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Affiliation(s)
- Mikhail Y Golovko
- Department of Pharmacology, University of North Dakota, Grand Forks, North Dakota 58202-9037, USA
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Liu K, Kozono D, Kato Y, Agre P, Hazama A, Yasui M. Conversion of aquaporin 6 from an anion channel to a water-selective channel by a single amino acid substitution. Proc Natl Acad Sci U S A 2005; 102:2192-7. [PMID: 15671159 PMCID: PMC548568 DOI: 10.1073/pnas.0409232102] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Aquaporin (AQP) 6 belongs to the aquaporin water channel family. Unlike other aquaporins, AQP6 functions not as a water channel but as an anion-selective channel. Single-channel analyses have shown AQP6 to flicker rapidly between closed and open status. The atomic structure of AQP1 and amino acid sequence alignments of the mammalian aquaporins reveal two well conserved glycine residues: Gly-57 in transmembrane helix (TM) 2 and Gly-173 in TM5 reside at the contact point where the two helices cross in human AQP1. Uniquely, all known mammalian orthologs of AQP6 have an asparagine residue (Asn-60) at the position corresponding to Gly-57. Here we show that a single residue substitution (N60G in rat AQP6) totally eliminates the anion permeability of AQP6 when expressed in Xenopus oocytes, but the N60G oocytes exhibit significantly higher osmotic water permeability under basal conditions. Replacement of the glycine at this site in AQP0, AQP1, and AQP2 blocked expression of the mutants at the oocyte plasma membrane. We propose that the asparagine residue at the contact point between TM2 and TM5 in AQP6 may function as a teeter board needed for rapid structural oscillations during anion permeation.
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Affiliation(s)
- Kun Liu
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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41
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Large V, Peroni O, Letexier D, Ray H, Beylot M. Metabolism of lipids in human white adipocyte. DIABETES & METABOLISM 2004; 30:294-309. [PMID: 15525872 DOI: 10.1016/s1262-3636(07)70121-0] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Adipose tissue is considered as the body's largest storage organ for energy in the form of triacylglycerols, which are mobilized through lipolysis process, to provide fuel to other organs and to deliver substrates to liver for gluconeogenesis (glycerol) and lipoprotein synthesis (free fatty acids). The release of glycerol and free fatty acids from human adipose tissue is mainly dependent on hormone-sensitive lipase which is intensively regulated by hormones and agents, such as insulin (inhibition of lipolysis) and catecholamines (stimulation of lipolysis). A special attention is paid to the recently discovered perilipins which could regulate the activity of the lipase hormono-sensible. Most of the plasma triacylglycerols are provided by dietary lipids, secreted from the intestine in the form of chylomicron or from the liver in the form of VLDL. Released into circulation as non-esterified fatty acids by lipoprotein lipase, those are taken up by adipose tissue via specific plasma fatty acid transporters (CD36, FATP, FABPpm) and used for triacylglycerol synthesis. A small part of triacylglycerols is synthesized into adipocytes from carbohydrates (lipogenesis) but its regulation is still debated in human. Physiological factors such as dieting/fasting regulate all these metabolic pathways, which are also modified in pathological conditions e.g. obesity.
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Affiliation(s)
- V Large
- INSERM 499, Faculté de médecine Laennec, rue Paradin, 69372 Lyon.
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Zheng L, Kostrewa D, Bernèche S, Winkler FK, Li XD. The mechanism of ammonia transport based on the crystal structure of AmtB of Escherichia coli. Proc Natl Acad Sci U S A 2004; 101:17090-5. [PMID: 15563598 PMCID: PMC535379 DOI: 10.1073/pnas.0406475101] [Citation(s) in RCA: 263] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2004] [Indexed: 11/18/2022] Open
Abstract
Ammonium is one of the most important nitrogen sources for bacteria, fungi, and plants, but it is toxic to animals. The ammonium transport proteins (methylamine permeases/ammonium transporters/rhesus) are present in all domains of life; however, functional studies with members of this family have yielded controversial results with respect to the chemical identity (NH(4)(+) or NH(3)) of the transported species. We have solved the structure of wild-type AmtB from Escherichia coli in two crystal forms at 1.8- and 2.1-A resolution, respectively. Substrate transport occurs through a narrow mainly hydrophobic pore located at the center of each monomer of the trimeric AmtB. At the periplasmic entry, a binding site for NH(4)(+) is observed. Two phenylalanine side chains (F107 and F215) block access into the pore from the periplasmic side. Further into the pore, the side chains of two highly conserved histidine residues (H168 and H318) bridged by a H-bond lie adjacent, with their edges pointing into the cavity. These histidine residues may facilitate the deprotonation of an ammonium ion entering the pore. Adiabatic free energy calculations support the hypothesis that an electrostatic barrier between H168 and H318 hinders the permeation of cations but not that of the uncharged NH(3.) The structural data and energetic considerations strongly indicate that the methylamine permeases/ammonium transporters/rhesus proteins are ammonia gas channels. Interestingly, at the cytoplasmic exit of the pore, two different conformational states are observed that might be related to the inactivation mechanism by its regulatory partner.
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Affiliation(s)
- Lei Zheng
- Biomolecular Research, Paul Scherrer Institut, CH-5232, Villigen, Switzerland
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Hedfalk K, Bill RM, Mullins JGL, Karlgren S, Filipsson C, Bergstrom J, Tamás MJ, Rydström J, Hohmann S. A Regulatory Domain in the C-terminal Extension of the Yeast Glycerol Channel Fps1p. J Biol Chem 2004; 279:14954-60. [PMID: 14752103 DOI: 10.1074/jbc.m313126200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Saccharomyces cerevisiae gene FPS1 encodes an aquaglyceroporin of the major intrinsic protein (MIP) family. The main function of Fps1p seems to be the efflux of glycerol in the adaptation of the yeast cell to lower external osmolarity. Fps1p is an atypical member of the family, because the protein is much larger (669 amino acids) than most MIPs due to long hydrophilic extensions in both termini. We have shown previously that a short domain in the N-terminal extension of the protein is required for restricting glycerol transport through the channel (Tamás, M. J., Karlgren, S., Bill, R. M., Hedfalk, K., Allegri, L., Ferreira, M., Thevelein, J. M., Rydström, J., Mullins, J. G. L., and Hohmann, S. (2003) J. Biol. Chem. 278, 6337-6345). Deletion of the N-terminal domain results in an unregulated channel, loss of glycerol, and osmosensitivity. In this work we have investigated the role of the Fps1p C terminus (139 amino acids). A set of eight truncations has been constructed and tested in vivo in a yeast fps1Delta strain. We have performed growth tests, membrane localization following cell fractionation, and glycerol accumulation measurements as well as an investigation of the osmotic stress response. Our results show that the C-terminal extension is also involved in restricting transport through Fps1p. We have identified a sequence of 12 amino acids, residues 535-546, close to the sixth transmembrane domain. This element seems to be important for controlling Fps1p function. Similar to the N-terminal domain, the C-terminal domain is amphiphilic and has a potential to dip into the membrane.
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Affiliation(s)
- Kristina Hedfalk
- Department of Cell and Molecular Biology/Microbiology, Götegorg University, Götegorg, Sweden.
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