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Cereghetti G, Kissling VM, Koch LM, Arm A, Schmidt CC, Thüringer Y, Zamboni N, Afanasyev P, Linsenmeier M, Eichmann C, Kroschwald S, Zhou J, Cao Y, Pfizenmaier DM, Wiegand T, Cadalbert R, Gupta G, Boehringer D, Knowles TPJ, Mezzenga R, Arosio P, Riek R, Peter M. An evolutionarily conserved mechanism controls reversible amyloids of pyruvate kinase via pH-sensing regions. Dev Cell 2024:S1534-5807(24)00271-5. [PMID: 38788715 DOI: 10.1016/j.devcel.2024.04.018] [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: 06/01/2022] [Revised: 10/15/2023] [Accepted: 04/26/2024] [Indexed: 05/26/2024]
Abstract
Amyloids are known as irreversible aggregates associated with neurodegenerative diseases. However, recent evidence shows that a subset of amyloids can form reversibly and fulfill essential cellular functions. Yet, the molecular mechanisms regulating functional amyloids and distinguishing them from pathological aggregates remain unclear. Here, we investigate the conserved principles of amyloid reversibility by studying the essential metabolic enzyme pyruvate kinase (PK) in yeast and human cells. We demonstrate that yeast PK (Cdc19) and human PK (PKM2) form reversible amyloids through a pH-sensitive amyloid core. Stress-induced cytosolic acidification promotes aggregation via protonation of specific glutamate (yeast) or histidine (human) residues within the amyloid core. Mutations mimicking protonation cause constitutive PK aggregation, while non-protonatable PK mutants remain soluble even upon stress. Physiological PK aggregation is coupled to metabolic rewiring and glycolysis arrest, causing severe growth defects when misregulated. Our work thus identifies an evolutionarily conserved, potentially widespread mechanism regulating functional amyloids during stress.
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Affiliation(s)
- Gea Cereghetti
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland; Centre for Misfolding Diseases, Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, UK.
| | - Vera M Kissling
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland; Particles-Biology Interactions Laboratory, Department of Materials Meet Life, Empa, 9014 St. Gallen, Switzerland
| | - Lisa M Koch
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Alexandra Arm
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Claudia C Schmidt
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Yannik Thüringer
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Nicola Zamboni
- Institute of Molecular Systems Biology, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Pavel Afanasyev
- Cryo-EM Knowledge Hub (CEMK), ETH Zurich, 8093 Zürich, Switzerland
| | - Miriam Linsenmeier
- Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland
| | - Cédric Eichmann
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland
| | - Sonja Kroschwald
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Jiangtao Zhou
- Department of Health Sciences & Technology, ETH Zürich, 8092 Zürich, Switzerland
| | - Yiping Cao
- Department of Health Sciences & Technology, ETH Zürich, 8092 Zürich, Switzerland
| | - Dorota M Pfizenmaier
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Thomas Wiegand
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland; Max Planck Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany; Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, 52074 Aachen, Germany
| | - Riccardo Cadalbert
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland
| | - Govind Gupta
- Particles-Biology Interactions Laboratory, Department of Materials Meet Life, Empa, 9014 St. Gallen, Switzerland
| | | | - Tuomas P J Knowles
- Centre for Misfolding Diseases, Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, UK
| | - Raffaele Mezzenga
- Department of Health Sciences & Technology, ETH Zürich, 8092 Zürich, Switzerland
| | - Paolo Arosio
- Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland
| | - Roland Riek
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland
| | - Matthias Peter
- Institute of Biochemistry, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland.
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Li SA, Meng XY, Zhang YJ, Chen CL, Jiao YX, Zhu YQ, Liu PP, Sun W. Progress in pH-Sensitive sensors: essential tools for organelle pH detection, spotlighting mitochondrion and diverse applications. Front Pharmacol 2024; 14:1339518. [PMID: 38269286 PMCID: PMC10806205 DOI: 10.3389/fphar.2023.1339518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Accepted: 12/20/2023] [Indexed: 01/26/2024] Open
Abstract
pH-sensitive fluorescent proteins have revolutionized the field of cellular imaging and physiology, offering insight into the dynamic pH changes that underlie fundamental cellular processes. This comprehensive review explores the diverse applications and recent advances in the use of pH-sensitive fluorescent proteins. These remarkable tools enable researchers to visualize and monitor pH variations within subcellular compartments, especially mitochondria, shedding light on organelle-specific pH regulation. They play pivotal roles in visualizing exocytosis and endocytosis events in synaptic transmission, monitoring cell death and apoptosis, and understanding drug effects and disease progression. Recent advancements have led to improved photostability, pH specificity, and subcellular targeting, enhancing their utility. Techniques for multiplexed imaging, three-dimensional visualization, and super-resolution microscopy are expanding the horizon of pH-sensitive protein applications. The future holds promise for their integration into optogenetics and drug discovery. With their ever-evolving capabilities, pH-sensitive fluorescent proteins remain indispensable tools for unravelling cellular dynamics and driving breakthroughs in biological research. This review serves as a comprehensive resource for researchers seeking to harness the potential of pH-sensitive fluorescent proteins.
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Affiliation(s)
- Shu-Ang Li
- Clinical Systems Biology Laboratories, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Xiao-Yan Meng
- Clinical Systems Biology Laboratories, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
- The Academy of Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Ying-Jie Zhang
- Clinical Systems Biology Laboratories, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
- The Academy of Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Cai-Li Chen
- Department of Immunology, School of Basic Medical Sciences, Xinxiang Medical University, Xinxiang, Henan, China
| | - Yu-Xue Jiao
- Clinical Systems Biology Laboratories, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Yong-Qing Zhu
- Clinical Systems Biology Laboratories, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
- The Academy of Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Pei-Pei Liu
- Clinical Systems Biology Laboratories, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Wei Sun
- Department of Burn and Repair Reconstruction, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
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3
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Luzia L, Lao‐Martil D, Savakis P, van Heerden J, van Riel N, Teusink B. pH dependencies of glycolytic enzymes of yeast under in vivo-like assay conditions. FEBS J 2022; 289:6021-6037. [PMID: 35429225 PMCID: PMC9790636 DOI: 10.1111/febs.16459] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 03/29/2022] [Accepted: 04/13/2022] [Indexed: 12/30/2022]
Abstract
Under carbon source transitions, the intracellular pH of Saccharomyces cerevisiae is subject to change. Dynamics in pH modulate the activity of the glycolytic enzymes, resulting in a change in glycolytic flux and ultimately cell growth. To understand how pH affects the global behavior of glycolysis and ethanol fermentation, we measured the activity of the glycolytic and fermentative enzymes in S. cerevisiae under in vivo-like conditions at different pH. We demonstrate that glycolytic enzymes exhibit differential pH dependencies, and optima, in the pH range observed during carbon source transitions. The forward reaction of GAPDH shows the highest decrease in activity, 83%, during a simulated feast/famine regime upon glucose removal (cytosolic pH drop from 7.1 to 6.4). We complement our biochemical characterization of the glycolytic enzymes by fitting the Vmax to the progression curves of product formation or decay over time. The fitting analysis shows that the observed changes in enzyme activities require changes in Vmax , but changes in Km cannot be excluded. Our study highlights the relevance of pH as a key player in metabolic regulation and provides a large set of quantitative data that can be explored to improve our understanding of metabolism in dynamic environments.
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Affiliation(s)
| | | | | | | | - Natal van Riel
- Department of Biomedical EngineeringTU EindhovenNetherlands
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4
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Aref M, Ranjbari E, García-Guzmán JJ, Hu K, Lork A, Crespo GA, Ewing AG, Cuartero M. Potentiometric pH Nanosensor for Intracellular Measurements: Real-Time and Continuous Assessment of Local Gradients. Anal Chem 2021; 93:15744-15751. [PMID: 34783529 PMCID: PMC8637545 DOI: 10.1021/acs.analchem.1c03874] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
![]()
We present a pH nanosensor
conceived for single intracellular measurements.
The sensing architecture consisted of a two-electrode system evaluated
in the potentiometric mode. We used solid-contact carbon nanopipette
electrodes tailored to produce both the indicator (pH nanosensor)
and reference electrodes. The indicator electrode was a membrane-based
ion-selective electrode containing a receptor for hydrogen ions that
provided a favorable selectivity for intracellular measurements. The
analytical features of the pH nanosensor revealed a Nernstian response
(slope of −59.5 mV/pH unit) with appropriate repeatability
and reproducibility (variation coefficients of <2% for the calibration
parameters), a fast response time (<5 s), adequate medium-term
drift (0.7 mV h–1), and a linear range of response
including physiological and abnormal cell pH levels (6.0–8.5).
In addition, the position and configuration of the reference electrode
were investigated in cell-based experiments to provide unbiased pH
measurements, in which both the indicator and reference electrodes
were located inside the same cell, each of them inside two neighboring
cells, or the indicator electrode inside the cell and the reference
electrode outside of (but nearby) the studied cell. Finally, the pH
nanosensor was applied to two cases: (i) the tracing of the pH gradient
from extra-to intracellular media over insertion into a single PC12
cell and (ii) the monitoring of variations in intracellular pH in
response to exogenous administration of pharmaceuticals. It is anticipated
that the developed pH nanosensor, which is a label-free analytical
tool, has high potential to aid in the investigation of pathological
states that manifest in cell pH misregulation, with no restriction
in the type of targeted cells.
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Affiliation(s)
- Mohaddeseh Aref
- Department of Chemistry, School of Engineering Science in Chemistry, Biochemistry and Health, Royal Institute of Technology, KTH, Stockholm SE-100 44, Sweden
| | - Elias Ranjbari
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemivägen 10, Gothenburg 41296, Sweden
| | - Juan José García-Guzmán
- Department of Chemistry, School of Engineering Science in Chemistry, Biochemistry and Health, Royal Institute of Technology, KTH, Stockholm SE-100 44, Sweden
| | - Keke Hu
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemivägen 10, Gothenburg 41296, Sweden
| | - Alicia Lork
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemivägen 10, Gothenburg 41296, Sweden
| | - Gaston A Crespo
- Department of Chemistry, School of Engineering Science in Chemistry, Biochemistry and Health, Royal Institute of Technology, KTH, Stockholm SE-100 44, Sweden
| | - Andrew G Ewing
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemivägen 10, Gothenburg 41296, Sweden
| | - Maria Cuartero
- Department of Chemistry, School of Engineering Science in Chemistry, Biochemistry and Health, Royal Institute of Technology, KTH, Stockholm SE-100 44, Sweden
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Metabolic Shifts as the Hallmark of Most Common Diseases: The Quest for the Underlying Unity. Int J Mol Sci 2021; 22:ijms22083972. [PMID: 33921428 PMCID: PMC8068795 DOI: 10.3390/ijms22083972] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Revised: 03/31/2021] [Accepted: 04/03/2021] [Indexed: 12/13/2022] Open
Abstract
A hyper-specialization characterizes modern medicine with the consequence of classifying the various diseases of the body into unrelated categories. Such a broad diversification of medicine goes in the opposite direction of physics, which eagerly looks for unification. We argue that unification should also apply to medicine. In accordance with the second principle of thermodynamics, the cell must release its entropy either in the form of heat (catabolism) or biomass (anabolism). There is a decreased flow of entropy outside the body due to an age-related reduction in mitochondrial entropy yield resulting in increased release of entropy in the form of biomass. This shift toward anabolism has been known in oncology as Warburg-effect. The shift toward anabolism has been reported in most diseases. This quest for a single framework is reinforced by the fact that inflammation (also called the immune response) is involved in nearly every disease. This strongly suggests that despite their apparent disparity, there is an underlying unity in the diseases. This also offers guidelines for the repurposing of old drugs.
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6
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Deng H, Li J, Zhou Y, Xia Y, Chen C, Zhou Z, Wu H, Wang P, Zhou S. Genetic engineering of circularly permuted yellow fluorescent protein reveals intracellular acidification in response to nitric oxide stimuli. Redox Biol 2021; 41:101943. [PMID: 33752109 PMCID: PMC8005830 DOI: 10.1016/j.redox.2021.101943] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Revised: 03/09/2021] [Accepted: 03/09/2021] [Indexed: 02/07/2023] Open
Abstract
Intracellular pH (pHi) is a crucial parameter in cell biology; thus, a series of pH probes have been developed to determine pHi changes in living cells. However, more sensitive and non-perturbing ratiometric pH probes are needed for accurate pHi measurements. While the fluorescence of circular permutated YFP (cpYFP) is hypersensitive to pH changes due to its intrinsic properties, the single excitation peak of this protein restricts its capacity of becoming a rational type of pH sensor. Herein, we collected several cpYFP-based probes with dual excitation peaks and constructed their corresponding loss-of-function mutants to screen for a potential competent pH probe. The most sensitive probe was named NocPer. NocPer consists of cpYFP inserted into inactive-mutated GAF and AAA+, which are two regulatory domains of E. coli NorR, a nitric oxide (NO)-specific transcription factor. Fluorescence emission of NocPer peaks at 517 nm while exhibiting dual excitation peaks at 420 and 495 nm, which can be used for ratiometric imaging. This new pH sensor has a large ratio response dynamic (pH range of 7.0–11.0), which covers the physiological pH range (pH 7.0–8.0), and exhibits an approximately 3-fold higher fluorescent signal in response to a pH increase from 7.0 to 8.0 than that of pHluorin. Using NocPer, we discovered a new biological phenomenon in which NO exposure decreases the E. coli pHi, which led to the hypothesis that pathogens decrease their own pHi during infection. Further, we elucidated that the NO-induced inhibition of cytochrome c oxidase in the respiratory chain is responsible for the decline in pHi, which might represent a protective strategy of E. coli under NO stress conditions. Our results demonstrated that NocPer is a ratiometric pH probe with high sensitivity for the physiological pH range. Circular permutated YFP was modified to be an a supersensitive and ratiometric pH probe NocPer. Nitric oxide (NO) lowering intracellular pH (pHi) was discovered as a new biological phenomenon. NO-induced inhibition of cytochrome c oxidase is responsible for the decline in pHi. pHi decrease by NO might represent a bacterial protective mechanism.
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Affiliation(s)
- Haitao Deng
- State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai, 200237, China
| | - Jingyi Li
- State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai, 200237, China
| | - Yao Zhou
- State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai, 200237, China
| | - Yang Xia
- State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai, 200237, China
| | - Chao Chen
- State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai, 200237, China
| | - Zhemin Zhou
- Key Laboratory of Industrial Biotechnology (Ministry of Education), School of Biotechnology, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu, 214122, China
| | - Hui Wu
- State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai, 200237, China
| | - Ping Wang
- State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai, 200237, China
| | - Shengmin Zhou
- State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai, 200237, China.
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Tian S, Liang X, Chen J, Zeng W, Zhou J, Du G. Enhancement of 2-phenylethanol production by a wild-type Wickerhamomyces anomalus strain isolated from rice wine. BIORESOURCE TECHNOLOGY 2020; 318:124257. [PMID: 33096442 DOI: 10.1016/j.biortech.2020.124257] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 10/08/2020] [Accepted: 10/09/2020] [Indexed: 06/11/2023]
Abstract
2-Phenylethanol (2-PE) is an important high-grade aromatic alcohol, which is widely used in the cosmetics, perfumery and food industries. However, 2-PE is mainly synthesized using a chemical route, which produces environmental pollution and harmful by-products. Screening of high-yielding wild-type strains has become an important goal for the future biosynthesis of 2-PE. In this study, a wild-type Wickerhamomyces anomalus was isolated from rice wine fermented mash. By optimizing the initial glucose and l-phenylalanine concentrations, 2630.7 mg/L of 2-PE was obtained in shaking flasks. The conditions of initial glucose and l-phenylalanine concentration, pH, and inoculation amount were optimized for 2-PE production with W. anomalus. Finally, based on the optimal conditions, the 2-PE titer reached 4,727.3 mg/L by a single-dose fed-batch strategy in a 5-L bioreactor. The results showed that the ability was expanded to harness the Ehrlich pathway for the production of high-value aromatics in aroma-producing yeast species.
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Affiliation(s)
- Shufang Tian
- Key Laboratory of Industrial Biotechnology, Ministry of Education and School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; National Engineering Laboratory for Cereal Fermentation Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; Science Center for Future Foods, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China
| | - Xiaolin Liang
- Key Laboratory of Industrial Biotechnology, Ministry of Education and School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; National Engineering Laboratory for Cereal Fermentation Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; Jiangsu Provisional Research Center for Bioactive Product Processing Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China
| | - Jian Chen
- Key Laboratory of Industrial Biotechnology, Ministry of Education and School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; Science Center for Future Foods, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China
| | - Weizhu Zeng
- Key Laboratory of Industrial Biotechnology, Ministry of Education and School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; National Engineering Laboratory for Cereal Fermentation Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; Jiangsu Provisional Research Center for Bioactive Product Processing Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China
| | - Jingwen Zhou
- Key Laboratory of Industrial Biotechnology, Ministry of Education and School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; National Engineering Laboratory for Cereal Fermentation Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; Science Center for Future Foods, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; Jiangsu Provisional Research Center for Bioactive Product Processing Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China.
| | - Guocheng Du
- Key Laboratory of Industrial Biotechnology, Ministry of Education and School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China; Science Center for Future Foods, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China.
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Zhao L, Zhao Y, Tang FL, Xiong L, Su C, Mei L, Zhu XJ, Xiong WC. pHluorin-BACE1-mCherry Acts as a Reporter for the Intracellular Distribution of Active BACE1 In Vitro and In Vivo. Cells 2019; 8:E474. [PMID: 31108937 PMCID: PMC6562731 DOI: 10.3390/cells8050474] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Revised: 05/09/2019] [Accepted: 05/15/2019] [Indexed: 12/23/2022] Open
Abstract
β-site APP-cleaving enzyme 1 (BACE1) initiates amyloid precursor protein (APP) cleavage and β-amyloid (Aβ) production, a critical step in the pathogenesis of Alzheimer's disease (AD). It is thus of considerable interest to investigate how BACE1 activity is regulated. BACE1 has its maximal activity at acidic pH and GFP variant-pHluorin-displays pH dependence. In light of these observations, we generated three tandem fluorescence-tagged BACE1 fusion proteins, named pHluorin-BACE1-mCherry, BACE1-mCherry-pHluorin and BACE1-mCherry-EGFP. Comparing the fluorescence characteristics of these proteins in response to intracellular pH changes induced by chloroquine or bafilomycin A1, we found that pHluorin-BACE1-mCherry is a better pH sensor for BACE1 because its fluorescence intensity responds to pH changes more dramatically and more quickly. Additionally, we found that (pro)renin receptor (PRR), a subunit of the v-ATPase complex, which is critical for maintaining vesicular pH, regulates pHluorin's fluorescence and BACE1 activity in pHluorin-BACE1-mCherry expressing cells. Finally, we found that the expression of Swedish mutant APP (APPswe) suppresses pHluorin fluorescence in pHluorin-BACE1-mCherry expressing cells in culture and in vivo, implicating APPswe not only as a substrate but also as an activator of BACE1. Taken together, these results suggest that the pHluorin-BACE1-mCherry fusion protein may serve as a useful tool for visualizing active/inactive BACE1 in culture and in vivo.
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Affiliation(s)
- Lu Zhao
- Key Laboratory of Molecular Epigenetics of Ministry of Education, Institute of Cytology and Genetics, Northeast Normal University, Changchun 130024, China.
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA.
| | - Yang Zhao
- Key Laboratory of Molecular Epigenetics of Ministry of Education, Institute of Cytology and Genetics, Northeast Normal University, Changchun 130024, China.
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
| | - Fu-Lei Tang
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA.
| | - Lei Xiong
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA.
| | - Ce Su
- Key Laboratory of Molecular Epigenetics of Ministry of Education, Institute of Cytology and Genetics, Northeast Normal University, Changchun 130024, China.
| | - Lin Mei
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA.
| | - Xiao-Juan Zhu
- Key Laboratory of Molecular Epigenetics of Ministry of Education, Institute of Cytology and Genetics, Northeast Normal University, Changchun 130024, China.
| | - Wen-Cheng Xiong
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA.
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9
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Genetically encoded fluorescent indicators for live cell pH imaging. Biochim Biophys Acta Gen Subj 2018; 1862:2924-2939. [PMID: 30279147 DOI: 10.1016/j.bbagen.2018.09.013] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 09/17/2018] [Accepted: 09/17/2018] [Indexed: 02/04/2023]
Abstract
BACKGROUND Intracellular pH underlies most cellular processes. There is emerging evidence of a pH-signaling role in plant cells and microorganisms. Dysregulation of pH is associated with human diseases, such as cancer and Alzheimer's disease. SCOPE OF REVIEW In this review, we attempt to provide a summary of the progress that has been made in the field during the past two decades. First, we present an overview of the current state of the design and applications of fluorescent protein (FP)-based pH indicators. Then, we turn our attention to the development and applications of hybrid pH sensors that combine the capabilities of non-GFP fluorophores with the advantages of genetically encoded tags. Finally, we discuss recent advances in multicolor pH imaging and the applications of genetically encoded pH sensors in multiparameter imaging. MAJOR CONCLUSIONS Genetically encoded pH sensors have proven to be indispensable noninvasive tools for selective targeting to different cellular locations. Although a variety of genetically encoded pH sensors have been designed and applied at the single cell level, there is still much room for improvements and future developments of novel powerful tools for pH imaging. Among the most pressing challenges in this area is the design of brighter redshifted sensors for tissue research and whole animal experiments. GENERAL SIGNIFICANCE The design of precise pH measuring instruments is one of the important goals in cell biochemistry and may give rise to the development of new powerful diagnostic tools for various diseases.
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10
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Reifenrath M, Boles E. A superfolder variant of pH-sensitive pHluorin for in vivo pH measurements in the endoplasmic reticulum. Sci Rep 2018; 8:11985. [PMID: 30097598 PMCID: PMC6086885 DOI: 10.1038/s41598-018-30367-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 07/27/2018] [Indexed: 11/09/2022] Open
Abstract
Many cellular processes are regulated via pH, and maintaining the pH of different organelles is crucial for cell survival. A pH-sensitive GFP variant, the so-called pHluorin, has proven to be a valuable tool to study the pH of the cytosol, mitochondria and other organelles in vivo. We found that the fluorescence intensity of Endoplasmic Reticulum (ER)-targeted pHluorin in the yeast Saccharomyces cerevisiae was very low and barely showed pH sensitivity, probably due to misfolding in the oxidative environment of the ER. We therefore developed a superfolder variant of pHluorin which enabled us to monitor pH changes in the ER and the cytosol of S. cerevisiae in vivo. The superfolder pHluorin variant is likely to be functional in cells of different organisms as well as in additional compartments that originate from the secretory pathway like the Golgi apparatus and pre-vacuolar compartments, and therefore has a broad range of possible future applications.
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Affiliation(s)
- Mara Reifenrath
- Institute of Molecular Biosciences, Faculty of Biological Sciences, Goethe University Frankfurt, Max-von-Laue Straße 9, 60438, Frankfurt am Main, Germany
| | - Eckhard Boles
- Institute of Molecular Biosciences, Faculty of Biological Sciences, Goethe University Frankfurt, Max-von-Laue Straße 9, 60438, Frankfurt am Main, Germany.
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11
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Flinck M, Kramer SH, Pedersen SF. Roles of pH in control of cell proliferation. Acta Physiol (Oxf) 2018; 223:e13068. [PMID: 29575508 DOI: 10.1111/apha.13068] [Citation(s) in RCA: 82] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Revised: 02/17/2018] [Accepted: 03/19/2018] [Indexed: 02/06/2023]
Abstract
Precise spatiotemporal regulation of intracellular pH (pHi ) is a prerequisite for normal cell function, and changes in pHi or pericellular pH (pHe ) exert important signalling functions. It is well established that proliferation of mammalian cells is dependent on a permissive pHi in the slightly alkaline range (7.0-7.2). It is also clear that mitogen signalling in nominal absence of HCO3- is associated with an intracellular alkalinization (~0.3 pH unit above steady-state pHi ), which is secondary to activation of Na+ /H+ exchange. However, it remains controversial whether this increase in pHi is part of the mitogenic signal cascade leading to cell cycle entry and progression, and whether it is relevant under physiological conditions. Furthermore, essentially all studies of pHi in mammalian cell proliferation have focused on the mitogen-induced G0-G1 transition, and the regulation and roles of pHi during the cell cycle remain poorly understood. The aim of this review is to summarize and critically discuss the possible roles of pHi and pHe in cell cycle progression. While the focus is on the mammalian cell cycle, important insights from studies in lower eukaryotes are also discussed. We summarize current evidence of links between cell cycle progression and pHi and discuss possible pHi - and pHe sensors and signalling pathways relevant to mammalian proliferation control. The possibility that changes in pHi during cell cycle progression may be an integral part of the checkpoint control machinery is explored. Finally, we discuss the relevance of links between pH and proliferation in the context of the perturbed pH homoeostasis and acidic microenvironment of solid tumours.
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Affiliation(s)
- M. Flinck
- Section for Cell Biology and Physiology; Department of Biology; Faculty of Science; University of Copenhagen; Copenhagen Denmark
| | - S. H. Kramer
- Section for Cell Biology and Physiology; Department of Biology; Faculty of Science; University of Copenhagen; Copenhagen Denmark
| | - S. F. Pedersen
- Section for Cell Biology and Physiology; Department of Biology; Faculty of Science; University of Copenhagen; Copenhagen Denmark
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12
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Rosenthal K, Oehling V, Dusny C, Schmid A. Beyond the bulk: disclosing the life of single microbial cells. FEMS Microbiol Rev 2017; 41:751-780. [PMID: 29029257 PMCID: PMC5812503 DOI: 10.1093/femsre/fux044] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Accepted: 09/08/2017] [Indexed: 01/08/2023] Open
Abstract
Microbial single cell analysis has led to discoveries that are beyond what can be resolved with population-based studies. It provides a pristine view of the mechanisms that organize cellular physiology, unbiased by population heterogeneity or uncontrollable environmental impacts. A holistic description of cellular functions at the single cell level requires analytical concepts beyond the miniaturization of existing technologies, defined but uncontrolled by the biological system itself. This review provides an overview of the latest advances in single cell technologies and demonstrates their potential. Opportunities and limitations of single cell microbiology are discussed using selected application-related examples.
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Affiliation(s)
- Katrin Rosenthal
- Department Solar Materials, Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany
- Laboratory of Chemical Biotechnology, Department of Biochemical & Chemical Engineering, TU Dortmund University, Dortmund, Germany
| | - Verena Oehling
- Department Solar Materials, Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany
- Laboratory of Chemical Biotechnology, Department of Biochemical & Chemical Engineering, TU Dortmund University, Dortmund, Germany
| | - Christian Dusny
- Department Solar Materials, Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany
| | - Andreas Schmid
- Department Solar Materials, Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany
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13
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Pal DS, Abbasi M, Mondal DK, Varghese BA, Paul R, Singh S, Datta R. Interplay between a cytosolic and a cell surface carbonic anhydrase in pH homeostasis and acid tolerance of Leishmania. J Cell Sci 2017; 130:754-766. [PMID: 28062849 DOI: 10.1242/jcs.199422] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Accepted: 12/23/2016] [Indexed: 12/11/2022] Open
Abstract
Leishmania parasites have evolved to endure the acidic phagolysosomal environment within host macrophages. How Leishmania cells maintain near-neutral intracellular pH and proliferate in such a proton-rich mileu remains poorly understood. We report here that, in order to thrive in acidic conditions, Leishmania major relies on a cytosolic and a cell surface carbonic anhydrase, LmCA1 and LmCA2, respectively. Upon exposure to acidic medium, the intracellular pH of the LmCA1+/-, LmCA2+/- and LmCA1+/-:LmCA2+/- mutant strains dropped by varying extents that led to cell cycle delay, growth retardation and morphological abnormalities. Intracellular acidosis and growth defects of the mutant strains could be reverted by genetic complementation or supplementation with bicarbonate. When J774A.1 macrophages were infected with the mutant strains, they exhibited much lower intracellular parasite burdens than their wild-type counterparts. However, these differences in intracellular parasite burden between the wild-type and mutant strains were abrogated if, before infection, the macrophages were treated with chloroquine to alkalize their phagolysosomes. Taken together, our results demonstrate that haploinsufficiency of LmCA1 and/or LmCA2 renders the parasite acid-susceptible, thereby unravelling a carbonic anhydrase-mediated pH homeostatic circuit in Leishmania cells.
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Affiliation(s)
- Dhiman Sankar Pal
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur-741246, West Bengal, India
| | - Mazharul Abbasi
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur-741246, West Bengal, India
| | - Dipon Kumar Mondal
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur-741246, West Bengal, India
| | - Binitha Anu Varghese
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur-741246, West Bengal, India
| | - Ritama Paul
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur-741246, West Bengal, India
| | - Shalini Singh
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur-741246, West Bengal, India
| | - Rupak Datta
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur-741246, West Bengal, India
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14
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Hernández-Villa G, Velasco-Bedrán H, González-Brambila M, Campos-Guzmán E. Influence of an Alkaline Zeolite on the Carbon Flow in Anaerobiosis of Three Strains of Saccharomyces cerevisiae. INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING 2016. [DOI: 10.1515/ijcre-2016-0023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Nowadays ethanol is considered an alternative to liquid fossil fuels, as a product of fermentation of sugars by Saccharomyces cerevisiae and other microorganisms. It is very important in the food, pharmaceutical and chemical industries. Prior studies show that the addition of certain amount of zeolite induces an increase in the ethanol/glucose yield. In this work, the effect of zeolite on the carbon flux of S. cerevisiae in different culture conditions is reported. An explanation for the effect of the zeolite on the yeast metabolism is offered. Results show a 20 % increase in yield, thus lowering production costs and improving the use of raw materials, which would increase the possibilities of using alcohol as biofuel.
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15
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Munder MC, Midtvedt D, Franzmann T, Nüske E, Otto O, Herbig M, Ulbricht E, Müller P, Taubenberger A, Maharana S, Malinovska L, Richter D, Guck J, Zaburdaev V, Alberti S. A pH-driven transition of the cytoplasm from a fluid- to a solid-like state promotes entry into dormancy. eLife 2016; 5. [PMID: 27003292 PMCID: PMC4850707 DOI: 10.7554/elife.09347] [Citation(s) in RCA: 277] [Impact Index Per Article: 34.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Accepted: 02/13/2016] [Indexed: 01/19/2023] Open
Abstract
Cells can enter into a dormant state when faced with unfavorable conditions. However, how cells enter into and recover from this state is still poorly understood. Here, we study dormancy in different eukaryotic organisms and find it to be associated with a significant decrease in the mobility of organelles and foreign tracer particles. We show that this reduced mobility is caused by an influx of protons and a marked acidification of the cytoplasm, which leads to widespread macromolecular assembly of proteins and triggers a transition of the cytoplasm to a solid-like state with increased mechanical stability. We further demonstrate that this transition is required for cellular survival under conditions of starvation. Our findings have broad implications for understanding alternative physiological states, such as quiescence and dormancy, and create a new view of the cytoplasm as an adaptable fluid that can reversibly transition into a protective solid-like state.
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Affiliation(s)
| | - Daniel Midtvedt
- Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Titus Franzmann
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Elisabeth Nüske
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Oliver Otto
- Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | - Maik Herbig
- Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | - Elke Ulbricht
- Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | - Paul Müller
- Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | - Anna Taubenberger
- Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | - Shovamayee Maharana
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Liliana Malinovska
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Doris Richter
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Jochen Guck
- Biotechnology Center, Technische Universität Dresden, Dresden, Germany
| | - Vasily Zaburdaev
- Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Simon Alberti
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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16
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Valkonen M, Penttilä M, Benčina M. Intracellular pH responses in the industrially important fungus Trichoderma reesei. Fungal Genet Biol 2014; 70:86-93. [PMID: 25046860 DOI: 10.1016/j.fgb.2014.07.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Revised: 07/07/2014] [Accepted: 07/08/2014] [Indexed: 12/14/2022]
Abstract
Preserving an optimal intracellular pH is critical for cell fitness and productivity. The pH homeostasis of the industrially important filamentous fungus Trichoderma reesei (Hypocrea jecorina) is largely unexplored. We analyzed the impact of growth conditions on regulation of intracellular pH of the strain Rut-C30 and the strain M106 derived from the Rut-C30 that accumulates L-galactonic acid-from provided galacturonic acid-as a consequence of L-galactonate dehydratase deletion. For live-cell measurements of intracellular pH, we used the genetically encoded ratiometric pH-sensitive fluorescent protein RaVC. Glucose and lactose, used as carbon sources, had specific effects on intracellular pH of T. reesei. The growth in lactose-containing medium extensively acidified cytosol, while intracellular pH of hyphae cultured in a medium with glucose remained at a higher level. The strain M106 maintained higher intracellular pH in the presence of D-galacturonic acid than its parental strain Rut-C30. Acidic external pH caused significant acidification of cytosol. Altogether, the pH homeostasis of T. reesei Rut-C30 strain is sensitive to extracellular pH and the degree of acidification depends on carbon source.
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Affiliation(s)
- Mari Valkonen
- VTT Technical Research Centre of Finland, Espoo, Finland.
| | - Merja Penttilä
- VTT Technical Research Centre of Finland, Espoo, Finland
| | - Mojca Benčina
- Laboratory of Biotechnology, National Institute of Chemistry, 1000 Ljubljana, Slovenia; Centre of Excellence EN-FIST, 1000 Ljubljana, Slovenia.
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17
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Kommuguri UN, Bodiga S, Bodiga VL. Role of mitochondrial respiration in sensitization of copper-deficient yeast to cisplatin-induced cytotoxicity. FRONTIERS IN LIFE SCIENCE 2014. [DOI: 10.1080/21553769.2014.882868] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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18
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Benčina M. Illumination of the spatial order of intracellular pH by genetically encoded pH-sensitive sensors. SENSORS 2013; 13:16736-58. [PMID: 24316570 PMCID: PMC3892890 DOI: 10.3390/s131216736] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Revised: 11/27/2013] [Accepted: 11/27/2013] [Indexed: 12/11/2022]
Abstract
Fluorescent proteins have been extensively used for engineering genetically encoded sensors that can monitor levels of ions, enzyme activities, redox potential, and metabolites. Certain fluorescent proteins possess specific pH-dependent spectroscopic features, and thus can be used as indicators of intracellular pH. Moreover, concatenated pH-sensitive proteins with target proteins pin the pH sensors to a definite location within the cell, compartment, or tissue. This study provides an overview of the continually expanding family of pH-sensitive fluorescent proteins that have become essential tools for studies of pH homeostasis and cell physiology. We describe and discuss the design of intensity-based and ratiometric pH sensors, their spectral properties and pH-dependency, as well as their performance. Finally, we illustrate some examples of the applications of pH sensors targeted at different subcellular compartments.
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Affiliation(s)
- Mojca Benčina
- Laboratory of Biotechnology, National Institute of Chemistry, 1000 Ljubljana, Slovenia.
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19
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Noninvasive high-throughput single-cell analysis of the intracellular pH of Saccharomyces cerevisiae by ratiometric flow cytometry. Appl Environ Microbiol 2013; 79:7179-87. [PMID: 24038689 DOI: 10.1128/aem.02515-13] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ability of cells to maintain pH homeostasis in response to environmental changes has elicited interest in basic and applied research and has prompted the development of methods for intracellular pH measurements. Many traditional methods provide information at population level and thus the average values of the studied cell physiological phenomena, excluding the fact that cell cultures are very heterogeneous. Single-cell analysis, on the other hand, offers more detailed insight into population variability, thereby facilitating a considerably deeper understanding of cell physiology. Although microscopy methods can address this issue, they suffer from limitations in terms of the small number of individual cells that can be studied and complicated image processing. We developed a noninvasive high-throughput method that employs flow cytometry to analyze large populations of cells that express pHluorin, a genetically encoded ratiometric fluorescent probe that is sensitive to pH. The method described here enables measurement of the intracellular pH of single cells with high sensitivity and speed, which is a clear improvement compared to previously published methods that either require pretreatment of the cells, measure cell populations, or require complex data analysis. The ratios of fluorescence intensities, which correlate to the intracellular pH, are independent of the expression levels of the pH probe, making the use of transiently or extrachromosomally expressed probes possible. We conducted an experiment on the kinetics of the pH homeostasis of Saccharomyces cerevisiae cultures grown to a stationary phase after ethanol or glucose addition and after exposure to weak acid stress and glucose pulse. Minor populations with pH homeostasis behaving differently upon treatments were identified.
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20
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Ullah A, Lopes MI, Brul S, Smits GJ. Intracellular pH homeostasis in Candida glabrata in infection-associated conditions. Microbiology (Reading) 2013; 159:803-813. [DOI: 10.1099/mic.0.063610-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Affiliation(s)
- Azmat Ullah
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
| | - Maria Inês Lopes
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
| | - Stanley Brul
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
| | - Gertien J. Smits
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
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21
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Ogoh K, Kinebuchi T, Murai M, Takahashi T, Ohmiya Y, Suzuki H. Dual-color-emitting green fluorescent protein from the sea cactus Cavernularia obesa and its use as a pH indicator for fluorescence microscopy. LUMINESCENCE 2013; 28:582-91. [PMID: 23468077 PMCID: PMC3884763 DOI: 10.1002/bio.2497] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 12/20/2012] [Accepted: 01/10/2013] [Indexed: 11/18/2022]
Abstract
We isolated and characterized a green fluorescent protein (GFP) from the sea cactus Cavernularia obesa. This GFP exists as a dimer and has absorption maxima at 388 and 498 nm. Excitation at 388 nm leads to blue fluorescence (456 nm maximum) at pH 5 and below, and green fluorescence (507 nm maximum) at pH 7 and above, and the GFP is remarkably stable at pH 4. Excitation at 498 nm leads to green fluorescence (507 nm maximum) from pH 5 to pH 9. We introduced five amino acid substitutions so that this GFP formed monomers rather than dimers and then used this monomeric form to visualize intracellular pH change during the phagocytosis of living cells by use of fluorescence microscopy. The intracellular pH change is visualized by use of a simple long-pass emission filter with single-wavelength excitation, which is technically easier to use than dual-emission fluorescent proteins that require dual-wavelength excitation. Copyright © 2013 John Wiley & Sons, Ltd.
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Affiliation(s)
- Katsunori Ogoh
- Corporate Research and Development Center, Olympus Corporation, Kuboyama 2-3, Hachioji, Tokyo 192-8512, Japan.
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22
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Guo L, Hu W, He X, Lux R, McLean J, Shi W. investigating acid production by Streptococcus mutans with a surface-displayed pH-sensitive green fluorescent protein. PLoS One 2013; 8:e57182. [PMID: 23468929 PMCID: PMC3585301 DOI: 10.1371/journal.pone.0057182] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 01/18/2013] [Indexed: 12/31/2022] Open
Abstract
Acidogenicity and aciduricity are the main virulence factors of the cavity-causing bacterium Streptococcus mutans. Monitoring at the individual cell level the temporal and spatial distribution of acid produced by this important oral pathogen is central for our understanding of these key virulence factors especially when S. mutans resides in multi-species microbial communities. In this study, we explored the application of pH-sensitive green fluorescent proteins (pHluorins) to investigate these important features. Ecliptic pHluorin was functionally displayed on the cell surface of S. mutans as a fusion protein with SpaP. The resulting strain (O87) was used to monitor temporal and spatial pH changes in the microenvironment of S. mutans cells under both planktonic and biofilm conditions. Using strain O87, we revealed a rapid pH drop in the microenviroment of S. mutans microcolonies prior to the decrease in the macro-environment pH following sucrose fermentation. Meanwhile, a non-uniform pH distribution was observed within S. mutans biofilms, reflecting differences in microbial metabolic activity. Furthermore, strain O87 was successfully used to monitor the S. mutans acid production profiles within dual- and multispecies oral biofilms. Based on these findings, the ecliptic pHluorin allows us to investigate in vivo and in situ acid production and distribution by the cariogenic species S. mutans.
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Affiliation(s)
- Lihong Guo
- School of Dentistry, University of California Los Angeles, Los Angeles, California, United States of America
| | - Wei Hu
- School of Dentistry, University of California Los Angeles, Los Angeles, California, United States of America
- State Key Laboratory of Microbial Technology, College of Life Science, Shandong University, Jinan, China
| | - Xuesong He
- School of Dentistry, University of California Los Angeles, Los Angeles, California, United States of America
| | - Renate Lux
- School of Dentistry, University of California Los Angeles, Los Angeles, California, United States of America
| | - Jeff McLean
- J. Craig Venter Institute, San Diego, California, United States of America
| | - Wenyuan Shi
- School of Dentistry, University of California Los Angeles, Los Angeles, California, United States of America
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23
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Dardalhon M, Kumar C, Iraqui I, Vernis L, Kienda G, Banach-Latapy A, He T, Chanet R, Faye G, Outten CE, Huang ME. Redox-sensitive YFP sensors monitor dynamic nuclear and cytosolic glutathione redox changes. Free Radic Biol Med 2012; 52:2254-65. [PMID: 22561702 PMCID: PMC3382975 DOI: 10.1016/j.freeradbiomed.2012.04.004] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 02/22/2012] [Accepted: 04/06/2012] [Indexed: 02/07/2023]
Abstract
Intracellular redox homeostasis is crucial for many cellular functions but accurate measurements of cellular compartment-specific redox states remain technically challenging. To better characterize redox control in the nucleus, we targeted a yellow fluorescent protein-based redox sensor (rxYFP) to the nucleus of the yeast Saccharomyces cerevisiae. Parallel analyses of the redox state of nucleus-rxYFP and cytosol-rxYFP allowed us to monitor distinctively dynamic glutathione (GSH) redox changes within these two compartments under a given condition. We observed that the nuclear GSH redox environment is highly reducing and similar to the cytosol under steady-state conditions. Furthermore, these sensors are able to detect redox variations specific for their respective compartments in glutathione reductase (Glr1) and thioredoxin pathway (Trr1, Trx1, Trx2) mutants that have altered subcellular redox environments. Our mutant redox data provide in vivo evidence that glutathione and the thioredoxin redox systems have distinct but overlapping functions in controlling subcellular redox environments. We also monitored the dynamic response of nucleus-rxYFP and cytosol-rxYFP to GSH depletion and to exogenous low and high doses of H₂O₂ bursts. These observations indicate a rapid and almost simultaneous oxidation of both nucleus-rxYFP and cytosol-rxYFP, highlighting the robustness of the rxYFP sensors in measuring real-time compartmental redox changes. Taken together, our data suggest that the highly reduced yeast nuclear and cytosolic redox states are maintained independently to some extent and under distinct but subtle redox regulation. Nucleus- and cytosol-rxYFP register compartment-specific localized redox fluctuations that may involve exchange of reduced and/or oxidized glutathione between these two compartments. Finally, we confirmed that GSH depletion has profound effects on mitochondrial genome stability but little effect on nuclear genome stability, thereby emphasizing that the critical requirement for GSH during growth is linked to a mitochondria-dependent process.
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Affiliation(s)
- Michèle Dardalhon
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Chitranshu Kumar
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Ismail Iraqui
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Laurence Vernis
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Guy Kienda
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Agata Banach-Latapy
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Tiantian He
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Roland Chanet
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Gérard Faye
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
| | - Caryn E. Outten
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, USA
| | - Meng-Er Huang
- Centre National de la Recherche Scientifique, UMR3348 “Genotoxic Stress and Cancer”, Centre Universitaire, 91405 Orsay, France
- Institut Curie, Centre de Recherche, Centre Universitaire, 91405 Orsay, France
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24
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Pineda Rodó A, Váchová L, Palková Z. In vivo determination of organellar pH using a universal wavelength-based confocal microscopy approach. PLoS One 2012; 7:e33229. [PMID: 22470445 PMCID: PMC3310042 DOI: 10.1371/journal.pone.0033229] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Accepted: 02/12/2012] [Indexed: 11/19/2022] Open
Abstract
Many essential cellular processes are affected by transmembrane H(+) gradients and intracellular pH (pHi). The research of such metabolic events calls for a non-invasive method to monitor pHi within individual subcellular compartments. We present a novel confocal microscopy approach for the determination of organellar pHi in living cells expressing pH-dependent ratiometric fluorescent proteins. Unlike conventional intensity-based fluorometry, our method relies on emission wavelength scans at single-organelle resolution to produce wavelength-based pH estimates both accurate and robust to low-signal artifacts. Analyses of Ato1p-pHluorin and Ato1p-mCherry yeast cells revealed previously unreported wavelength shifts in pHluorin emission which, together with ratiometric mCherry, allowed for high-precision quantification of actual physiological pH values and evidenced dynamic pHi changes throughout the different stages of yeast colony development. Additionally, comparative pH quantification of Ato1p-pHluorin and Met17p-pHluorin cells implied the existence of a significant pHi gradient between peripheral and internal cytoplasm of cells from colonies occurring in the ammonia-producing alkali developmental phase. Results represent a step forward in the study of pHi regulation and subcellular metabolic functions beyond the scope of this study.
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Affiliation(s)
- Albert Pineda Rodó
- Department of Genetics and Microbiology, Charles University, Prague, Czech Republic
| | - Libuše Váchová
- Department of Genetics and Microbiology, Charles University, Prague, Czech Republic
- Institute of Microbiology, Academy of Sciences, Prague, Czech Republic
| | - Zdena Palková
- Department of Genetics and Microbiology, Charles University, Prague, Czech Republic
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Orij R, Brul S, Smits GJ. Intracellular pH is a tightly controlled signal in yeast. Biochim Biophys Acta Gen Subj 2011; 1810:933-44. [PMID: 21421024 DOI: 10.1016/j.bbagen.2011.03.011] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Revised: 03/15/2011] [Accepted: 03/15/2011] [Indexed: 11/25/2022]
Abstract
BACKGROUND Nearly all processes in living cells are pH dependent, which is why intracellular pH (pH(i)) is a tightly regulated physiological parameter in all cellular systems. However, in microbes such as yeast, pH(i) responds to extracellular conditions such as the availability of nutrients. This raises the question of how pH(i) dynamics affect cellular function. SCOPE OF REVIEW We discuss the control of pH(i,) and the regulation of processes by pH(i), focusing on the model organism Saccharomyces cerevisiae. We aim to dissect the effects of pH(i) on various aspects of cell physiology, which are often intertwined. Our goal is to provide a broad overview of how pH(i) is controlled in yeast, and how pH(i) in turn controls physiology, in the context of both general cellular functioning as well as of cellular decision making upon changes in the cell's environment. MAJOR CONCLUSIONS Besides a better understanding of the regulation of pH(i), evidence for a signaling role of pH(i) is accumulating. We conclude that pH(i) responds to nutritional cues and relays this information to alter cellular make-up and physiology. The physicochemical properties of pH allow the signal to be fast, and affect multiple regulatory levels simultaneously. GENERAL SIGNIFICANCE The mechanisms for regulation of processes by pH(i) are tightly linked to the molecules that are part of all living cells, and the biophysical properties of the signal are universal amongst all living organisms, and similar types of regulation are suggested in mammals. Therefore, dynamic control of cellular decision making by pH(i) is therefore likely a general trait. This article is part of a Special Issue entitled: Systems Biology of Microorganisms.
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Affiliation(s)
- Rick Orij
- Swammerdam Institute for Life Sciences, University of Amsterdam, the Netherlands.
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Antosiewicz JM, Shugar D. Poisson–Boltzmann continuum-solvation models: applications to pH-dependent properties of biomolecules. MOLECULAR BIOSYSTEMS 2011; 7:2923-49. [DOI: 10.1039/c1mb05170a] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Maresová L, Hosková B, Urbánková E, Chaloupka R, Sychrová H. New applications of pHluorin--measuring intracellular pH of prototrophic yeasts and determining changes in the buffering capacity of strains with affected potassium homeostasis. Yeast 2010; 27:317-25. [PMID: 20148390 DOI: 10.1002/yea.1755] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
pHluorin is a pH-sensitive variant of green fluorescent protein for measuring intracellular pH (pH(in)) in living cells. We constructed a new pHluorin plasmid with the dominant selection marker KanMX. This plasmid allows pH measurements in cells without auxotrophic mutations and/or grown in chemically indefinite media. We observed differing values of pH(in) for three prototrophic wild-types. The new construct was also used to determine the pH(in) in strains differing in the activity of the plasma membrane Pma1 H(+)-ATPase and the influence of glucose on pH(in). We describe in detail pHluorin measurements performed in a microplate reader, which require much less hands-on time and much lower cell culture volumes compared to standard cuvettes measurements. We also utilized pHluorin in a new method of measuring the buffering capacity of yeast cell cytosol in vivo, shown to be ca. 52 mM/pH for wild-type yeast and moderately decreased in mutants with affected potassium transport.
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Affiliation(s)
- Lydie Maresová
- Department of Membrane Transport, Institute of Physiology, Academy of Sciences of the Czech Republic, v.v.i., Videnska 1083, 142 20 Prague 4, Czech Republic.
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Enhancing stress resistance and production phenotypes through transcriptome engineering. Methods Enzymol 2010; 470:509-32. [PMID: 20946823 DOI: 10.1016/s0076-6879(10)70020-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/23/2023]
Abstract
As Saccharomyces cerevisiae is engineered further as a microbial factory for industrially relevant but potentially cytotoxic molecules such as ethanol, issues of cell viability arise that threaten to place a biological limit on output capacity and/or the use of less refined production conditions. Evidence suggests that one naturally evolved mode of survival in deleterious environments involves the complex, multigenic interplay between disparate stress response and homeostasis mechanisms. Rational engineering of such resistance would require a systems-level understanding of cellular behavior that is, in general, not yet available. To circumvent this limitation, we have developed a phenotype discovery approach termed global transcription machinery engineering (gTME) that allows for the generation and selection of nonphysiological traits. We alter gene expression on a genome-wide scale by selecting for dominant mutations in a randomly mutagenized general transcription factor. The gene encoding the mutated transcription factor resides on a plasmid in a strain carrying the unaltered chromosomal allele. Thus, although the dominant mutations may destroy the essential function of the plasmid-borne variant, alteration of the transcriptome with minimal perturbation to normal cellular processes is possible via the presence of the native genomic allele. Achieving a phenotype of interest involves the construction and diversity evaluation of yeast libraries harboring random sequence variants of a chosen transcription factor and the subsequent selection and validation of mutant strains. We describe the rationale and procedures associated with each step in the context of generating strains possessing enhanced ethanol tolerance.
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Acquisti C, Kumar S, Elser JJ. Signatures of nitrogen limitation in the elemental composition of the proteins involved in the metabolic apparatus. Proc Biol Sci 2009; 276:2605-10. [PMID: 19369262 DOI: 10.1098/rspb.2008.1960] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Nitrogen (N) is a fundamental component of nucleotides and amino acids and is often a limiting nutrient in natural ecosystems. Thus, study of the N content of biomolecules may establish important connections between ecology and genomics. However, while significant differences in the elemental composition of whole organisms are well documented, how the flux of nutrients in the cell has shaped the evolution of different cellular processes remains poorly understood. By examining the elemental composition of major functional classes of proteins in four multicellular eukaryotic model organisms, we find that the catabolic machinery shows substantially lower N content than the anabolic machinery and the rest of the proteome. This pattern suggests that ecological selection for N conservation specifically targets cellular components that are highly expressed in response to nutrient limitation. We propose that the RNA component of the anabolic machineries is the mechanistic force driving the elemental imbalance we found, and that RNA functions as an intracellular nutrient reservoir that is degraded and recycled during starvation periods. A comparison of the elemental composition of the anabolic and catabolic machineries in species that have experienced different levels of N limitation in their evolutionary history (animals versus plants) suggests that selection for N conservation has preferentially targeted the catabolic machineries of plants, resulting in a lower N content of the proteins involved in their catabolic processes. These findings link the composition of major cellular components to the environmental factors that trigger the activation of those components, suggesting that resource availability has constrained the atomic composition and the molecular architecture of the biotic processes that enable cells to respond to reduced nutrient availability.
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Affiliation(s)
- Claudia Acquisti
- Biodesign Institute, Center for Evolutionary Functional Genomics, Arizona State University, Tempe, AZ 85287-5301, USA.
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Dündar E, Bush DR. BAT1, a bidirectional amino acid transporter in Arabidopsis. PLANTA 2009; 229:1047-56. [PMID: 19199104 DOI: 10.1007/s00425-009-0892-8] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2008] [Accepted: 01/12/2009] [Indexed: 05/08/2023]
Abstract
The Arabidopsis thaliana At2g01170 gene is annotated as a putative gamma amino butyric acid (GABA) permease based on its sequence similarity to a yeast GABA transporting gene (UGA4). A cDNA of At2g01170 was expressed in yeast and analyzed for amino acid transport activity. Both direct measurement of amino acid transport and yeast growth experiments demonstrated that the At2g01170 encoded-protein exhibits transport activity for alanine, arginine, glutamate and lysine, but not for GABA or proline. Significantly, unlike other amino acid transporters described in plants to date, At2g01170 displayed both export and import activity. Based on that observation, it was named bidirectional amino acid transporter 1 (BAT1). Sequence comparisons show BAT1 is not a member of any previously defined amino acid transporter family. It does share, however, several conserved protein domains found in a variety of prokaryotic and eukaryotic amino acid transporters, suggesting membership in an ancient family of transporters. BAT1 is a single copy gene in the Arabidopsis genome, and its mRNA is ubiquitously expressed in all organs. A transposon--GUS gene-trap insert in the BAT1 gene displays GUS localization in the vascular tissues (Dundar in Ann Appl Biol, 2009) suggesting BAT1 may function in amino acid export from the phloem into sink tissues.
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Affiliation(s)
- Ekrem Dündar
- Biyoloji Bölümü, Fen Edebiyat Fakültesi, Balikesir Universitesi, Balikesir, Turkey.
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Live-Cell imaging and measurement of intracellular pH in filamentous fungi using a genetically encoded ratiometric probe. EUKARYOTIC CELL 2009; 8:703-12. [PMID: 19286983 DOI: 10.1128/ec.00333-08] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A novel, genetically encoded, ratiometric pH probe (RaVC) was constructed to image and measure intracellular pH in living hyphae of Aspergillus niger. RaVC is a chimeric protein based on the pH-sensitive probe pHluorin, which was partially codon optimized for expression in Aspergillus. Intracellular pH imaging and measurement was performed by simultaneous, dual-excitation confocal ratio imaging. The mean cytoplasmic pH measured was 7.4 to 7.7 based on calibrating RaVC in situ within nigericin-treated hyphae. Pronounced, longitudinal cytoplasmic pH gradients were not observed in the apical 20 microm of actively growing hyphae at the periphery of 18-h-old colonies. The cytoplasmic pH remained unchanged after prolonged growth in buffered medium with pH values between 2.5 or 9.5. Sudden changes in external pH significantly changed cytoplasmic pH by <1.3 pH units, but it returned to its original value within 20 min following treatment. The weak acid and antifungal food preservative sorbic acid caused prolonged, concentration-dependent intracellular acidification. The inhibition of ATPases with N-ethylmaleimide, dicychlohexylcarbodimide, or sodium azide caused the cytoplasmic pH to decrease by <1 pH unit. Treatment with the protonophore carbonyl cyanide m-chlorophenylhydrazone or cyanide p-(trifluoromethoxy) phenylhydrazone reduced the cytoplasmic pH by <1 pH unit. In older hyphae from 32-h-old cultures, RaVC became sequestered within large vacuoles, which were shown to have pH values between 6.2 and 6.5. Overall, our study demonstrates that RaVC is an excellent probe for visualizing and quantifying intracellular pH in living fungal hyphae.
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Orij R, Postmus J, Ter Beek A, Brul S, Smits GJ. In vivo measurement of cytosolic and mitochondrial pH using a pH-sensitive GFP derivative in Saccharomyces cerevisiae reveals a relation between intracellular pH and growth. MICROBIOLOGY-SGM 2009; 155:268-278. [PMID: 19118367 DOI: 10.1099/mic.0.022038-0] [Citation(s) in RCA: 253] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The specific pH values of cellular compartments affect virtually all biochemical processes, including enzyme activity, protein folding and redox state. Accurate, sensitive and compartment-specific measurements of intracellular pH (pHi) dynamics in living cells are therefore crucial to the understanding of stress response and adaptation. We used the pH-sensitive GFP derivative 'ratiometric pHluorin' expressed in the cytosol and in the mitochondrial matrix of growing Saccharomyces cerevisiae to assess the variation in cytosolic pH (pHcyt) and mitochondrial pH (pHmit) in response to nutrient availability, respiratory chain activity, shifts in environmental pH and stress induced by addition of sorbic acid. The in vivo measurement allowed accurate determination of organelle-specific pH, determining a constant pHcyt of 7.2 and a constant pHmit of 7.5 in cells exponentially growing on glucose. We show that pHcyt and pHmit are differentially regulated by carbon source and respiratory chain inhibitors. Upon glucose starvation or sorbic acid stress, pHi decrease coincided with growth stasis. Additionally, pHi and growth coincided similarly in recovery after addition of glucose to glucose-starved cultures or after recovery from a sorbic acid pulse. We suggest a relation between pHi and cellular energy generation, and therefore a relation between pHi and growth.
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Affiliation(s)
- Rick Orij
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
| | - Jarne Postmus
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
| | - Alex Ter Beek
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
| | - Stanley Brul
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
| | - Gertien J Smits
- Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands
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Mutagenesis of the bacterial RNA polymerase alpha subunit for improvement of complex phenotypes. Appl Environ Microbiol 2009; 75:2705-11. [PMID: 19251886 DOI: 10.1128/aem.01888-08] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Combinatorial or random methods for strain engineering have been extensively used for the improvement of multigenic phenotypes and other traits for which the underlying mechanism is not fully understood. Although the preferred method has traditionally been mutagenesis and selection, our laboratory has successfully used mutant transcription factors, which direct the RNA polymerase (RNAP) during transcription, to engineer complex phenotypes in microbial cells. Here, we show that it is also possible to impart new phenotypes by altering the RNAP core enzyme itself, in particular through mutagenesis of the alpha subunit of the bacterial polymerase. We present the use of this tool for improving tolerance of Escherichia coli to butanol and other solvents and for increasing the titers of two commercially relevant products, L-tyrosine and hyaluronic acid. In addition, we explore the underlying physiological changes that give rise to the solvent-tolerant mutant.
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Green fluorescent protein based pH indicators for in vivo use: a review. Anal Bioanal Chem 2008; 393:1107-22. [DOI: 10.1007/s00216-008-2515-9] [Citation(s) in RCA: 123] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2008] [Revised: 11/03/2008] [Accepted: 11/05/2008] [Indexed: 10/21/2022]
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Sapienza K, Bannister W, Balzan R. Mitochondrial involvement in aspirin-induced apoptosis in yeast. MICROBIOLOGY-SGM 2008; 154:2740-2747. [PMID: 18757807 DOI: 10.1099/mic.0.2008/017228-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
We have previously reported that aspirin induces apoptosis in manganese superoxide dismutase (MnSOD)-deficient Saccharomyces cerevisiae cells when cultivated on the non-fermentable carbon source ethanol. Here, we investigated the role of mitochondria in aspirin-induced apoptosis. We report that aspirin had an inhibitory effect on cellular respiration, and caused the release of most of the mitochondrial cytochrome c and a dramatic drop in the mitochondrial membrane potential (DeltaPsi(m)). Also, aspirin reduced the intracellular cytosolic pH in the MnSOD-deficient cells growing in ethanol medium, but this did not seem to be the initial trigger that committed these cells to aspirin-induced apoptosis. Furthermore, loss of DeltaPsi(m) was not required for aspirin-induced release of cytochrome c, since the initial release of cytochrome c occurred prior to the disruption of the DeltaPsi(m). It is thus possible that cytochrome c release does not involve the early onset of the mitochondrial permeability transition, but only an alteration of the permeability of the outer mitochondrial membrane.
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Affiliation(s)
- Karen Sapienza
- Department of Physiology and Biochemistry, University of Malta, Msida MSD 2080, Malta
| | - William Bannister
- Department of Physiology and Biochemistry, University of Malta, Msida MSD 2080, Malta
| | - Rena Balzan
- Department of Physiology and Biochemistry, University of Malta, Msida MSD 2080, Malta
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Kuhn Y, Rohrbach P, Lanzer M. Quantitative pH measurements in Plasmodium falciparum-infected erythrocytes using pHluorin. Cell Microbiol 2007; 9:1004-13. [PMID: 17381432 DOI: 10.1111/j.1462-5822.2006.00847.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The digestive vacuole of the malaria parasite Plasmodium falciparum is the site of action of several antimalarial drugs, such as chloroquine, which accumulate in this organelle due to their properties as amphiphilic weak bases that inhibit haem detoxification. It has been suggested that changes in the pH of the digestive vacuole, affecting either drug partitioning or haem solubility and/or biomineralization rates, would correlate with reduced intracellular chloroquine accumulation and, hence, would determine the chloroquine-resistance phenotype. The techniques previously used to quantify digestive vacuolar pH mainly relied on lysed or isolated parasites, with unpredictable consequences on internal pH homeostasis. In this study, we have investigated the baseline steady-state pH of the cytoplasm and digestive vacuole of a chloroquine-sensitive (HB3) and a chloroquine-resistant (Dd2) parasite using a pH-sensitive green fluorescent protein, termed pHluorin. This non-invasive technique allows for in vivo pH measurements in intact P. falciparum-infected erythrocytes under physiological conditions. The data suggest that the pH of the cytoplasm is approximately 7.15 +/- 0.07 and that of the digestive vacuole approximately 5.18 +/- 0.05. No significant differences in baseline pH values were recorded for the chloroquine-sensitive and chloroquine-resistant parasites.
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Affiliation(s)
- Yvonne Kuhn
- Hygiene Institut, Abteilung Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
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Phillips SN, Muzaffar N, Codlin S, Korey CA, Taschner PEM, de Voer G, Mole SE, Pearce DA. Characterizing pathogenic processes in Batten disease: Use of small eukaryotic model systems. Biochim Biophys Acta Mol Basis Dis 2006; 1762:906-19. [PMID: 17049819 DOI: 10.1016/j.bbadis.2006.08.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Revised: 08/08/2006] [Accepted: 08/27/2006] [Indexed: 10/24/2022]
Abstract
The neuronal ceroid lipofuscinoses (NCLs) are neurodegenerative disorders. Nevertheless, small model organisms, including those lacking a nervous system, have proven invaluable in the study of mechanisms that underlie the disease and in studying the functions of the conserved proteins associated to each disease. From the single-celled yeast, Saccharomyces cerevisiae and Schizosaccharomyces pombe, to the worm, Caenorhabditis elegans and the fruitfly, Drosophila melanogaster, biochemical and, in particular, genetic studies on these organisms have provided insight into the NCLs.
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Affiliation(s)
- Seasson N Phillips
- Center for Aging and Developmental Biology, Aab Institute of Biomedical Science, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
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Fliegel L, Wiebe C, Chua G, Young PG. Functional expression and cellular localization of the Na+/H+ exchanger Sod2 of the fission yeast Schizosaccharomyces pombe. Can J Physiol Pharmacol 2006; 83:565-72. [PMID: 16091782 DOI: 10.1139/y05-044] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the fission yeast Schizosaccharomyces pombe, the Na+/H+ exchanger, Sod2, plays a major role in the removal of excess intracellular sodium, and its disruption results in a sodium-sensitive phenotype. We examined the subcellular distribution and dynamics of Sod2 expression in S. pombe using a sod2-GFP fusion protein under the control of an attenuated version of the inducible nmt promoter. Sod2 was localized throughout the plasma membrane, the nuclear envelope, and some internal membrane systems. In exponentially growing cells, in which sod2-GFP was expressed and then the promoter turned-off, previously synthesized sod2-GFP was stable for long periods and found localized to the plasma membrane in the medial regions of the cell. It was not present at the actively growing cell ends. This suggests that these regions of the cell contain old plasma membrane protein vs. newly synthesized plasma membrane without Sod2 at the growing ends. Sod2 localization was not affected by salt stress. The results suggest that Sod2 is both a plasma membrane protein and is present in intracellular membranes. It is likely tethered within discrete regions of the plasma membrane and is not free to diffuse throughout the bilayer.
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Affiliation(s)
- Larry Fliegel
- Department of Biochemistry, 347 Medical Science Building, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
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Bond J, Varley J. Use of flow cytometry and SNARF to calibrate and measure intracellular pH in NS0 cells. Cytometry A 2005; 64:43-50. [PMID: 15688357 DOI: 10.1002/cyto.a.20066] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND Two calibration methods have been proposed for determining the relation between the fluorescence ratio of a pH-sensitive fluorescent indicator and intracellular pH (pHi). The first method uses nigericin to clamp pHi to external pH (pHe) and the second is the null point method. We compared these different calibration methods, solution conditions, and temperatures by using flow cytometry and the fluorescent dye 1,5- (and-6)-carboxy seminaphtorhodafluor-1-acetoxymethyl ester with an NS0 cell line. METHODS The nigericin method was performed in glucose solutions supplemented with KCl and 2-(N-morpholino)ethane sulphonic acid plus tris(hydroxymethyl)aminomethane (solution 1A), a mixture of K2HPO4/KH2PO4 in glucose-solution supplemented solutions (solution 2A), or bicarbonate buffered growth medium supplemented with K2HPO4/KH2PO4 (solution 2B); this allowed a range of pHe values to be used. The effect of temperature (22 degrees C or 37 degrees C) on the nigericin calibration curve was also investigated. The null point method was performed by using a series of solutions with a mixture of weak acid and base with a known pHi response. RESULTS Using solution 1A as the calibration solution resulted in acidic values of pHi for cells cultured in medium as compared with the values achieved with solution 2A. Using solution 2B did not affect the calibration curve. For the temperatures considered in this study, there was no affect on the calibration curve, but temperature did affect the pHi value of cells in phosphate buffered saline. The pseudo-null point method used with flow cytometry resulted in a calibration curve that was significantly different (P<0.05) from that achieved using the nigericin method. CONCLUSIONS Our data indicates that the choice of calibration solution can affect the reported pHi value; therefore, careful choice of solution is important.
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Affiliation(s)
- Jennifer Bond
- Department of Chemical Engineering and Chemical Technology, Imperial College, London, United Kingdom
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Valli M, Sauer M, Branduardi P, Borth N, Porro D, Mattanovich D. Intracellular pH distribution in Saccharomyces cerevisiae cell populations, analyzed by flow cytometry. Appl Environ Microbiol 2005; 71:1515-21. [PMID: 15746355 PMCID: PMC1065191 DOI: 10.1128/aem.71.3.1515-1521.2005] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Intracellular pH has an important role in the maintenance of the normal functions of yeast cells. The ability of the cell to maintain this pH homeostasis also in response to environmental changes has gained more and more interest in both basic and applied research. In this study we describe a protocol which allows the rapid determination of the intracellular pH of Saccharomyces cerevisiae cells. The method is based on flow cytometry and employs the pH-dependent fluorescent probe carboxy SNARF-4F. The protocol attempts to minimize the perturbation of the system under study, thus leading to accurate information about the physiological state of the single cell. Moreover, statistical analysis performed on major factors that may influence the final determination supported the validity of the optimized protocol. The protocol was used to investigate the effect of external pH on S. cerevisiae cells incubated in buffer. The results obtained showed that stationary cells are better able than exponentially grown cells to maintain their intracellular pH homeostasis independently of external pH changes. Furthermore, analysis of the intracellular pH distribution within the cell populations highlighted the presence of subpopulations characterized by different intracellular pH values. Notably, a different behavior was observed for exponentially grown and stationary cells in terms of the appearance and development of these subpopulations as a response to a changing external pH.
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Affiliation(s)
- Minoska Valli
- Institute of Applied Microbiology, University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria
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Sun N, Jang J, Lee S, Kim S, Lee S, Hoe KL, Chung KS, Kim DU, Yoo HS, Won M, Song KB. The first two-dimensional reference map of the fission yeast,Schizosaccharomyces pombe proteins. Proteomics 2005; 5:1574-9. [PMID: 15800968 DOI: 10.1002/pmic.200401053] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Cytosolic proteins of Schizosaccharomyces pombe were separated by two-dimensional (2-D) gel electrophoresis, to construct the first 2-D reference map. In the pI range 4-7, more than 500 spots were detected by silver staining, and 70 different proteins corresponding to 111 spots were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and tandem mass spectrometry, where necessary. In the pI range 6-9, approximately 330 spots were detected, and 31 proteins corresponding to 38 spots were identified by mass spectrometry. More than 50% of the identified proteins were involved in amino acid, carbohydrate or nucleotide metabolism, and energy production. A second large group of identified proteins comprises heat shock and other stress related proteins and chaperones.
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Affiliation(s)
- Namkyu Sun
- Laboratory of Protein Chemistry, Chungnam National University, Daejeon, South Korea
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Schuster S, Enzelberger M, Trauthwein H, Schmid RD, Urlacher VB. pHluorin-Based in Vivo Assay for Hydrolase Screening. Anal Chem 2005; 77:2727-32. [PMID: 15859586 DOI: 10.1021/ac0486692] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
pHluorin, a pH-sensitive mutant of green fluorescent protein (GFP), acts as a sensor for intracellular pH shifts, triggered by hydrolytic enzymes. This principle was used to develop a pHluorin-based in vivo assay for hydrolase screening. The presented assay was evaluated for Escherichia coli (E. coli) cells, producing heterologous pHluorin and an esterase from Geobacillus stearothermophilus which is considered as a model hydrolase. Subsequently, the utility of this detection system was also demonstrated with recombinantly expressed hydantoinase and amidase in E. coli. This in vivo assay also shows capability for readout with flow cytometric devices. Population shifts of pHluorin-expressing E. coli cells were easily recognized due to pH changes caused by substrate hydrolysis.
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Affiliation(s)
- Sascha Schuster
- Institute of Technical Biochemistry, University of Stuttgart, Allmandring 31, D-70569 Stuttgart, Germany
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Abstract
Gastrointestinal pathogens are faced with an extremely acidic environment. Within moments, a pathogen such as Escherichia coli O157:H7 can move from the nurturing pH 7 environment of a hamburger to the harsh pH 2 milieu of the stomach. Surprisingly, certain microorganisms that grow at neutral pH have elegantly regulated systems that enable survival during excursions into acidic environments. The best-characterized acid-resistance system is found in E. coli.
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Affiliation(s)
- John W Foster
- Department of Microbiology and Immunology, University of South Alabama College of Medicine, Mobile, Alabama 36695, USA.
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Mishra M, Karagiannis J, Trautmann S, Wang H, McCollum D, Balasubramanian MK. The Clp1p/Flp1p phosphatase ensures completion of cytokinesis in response to minor perturbation of the cell division machinery in Schizosaccharomyces pombe. J Cell Sci 2004; 117:3897-910. [PMID: 15265986 DOI: 10.1242/jcs.01244] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Fission yeast mutants defective in actomyosin ring formation and function exhibit a prolonged G2 delay following cytokinesis failure. This G2 delay depends on the SIN, a signaling network essential for cytokinesis, and the non-essential Cdc14p family phosphatase, Clp1p/Flp1p and has been proposed to signify a cytokinesis checkpoint mechanism. However, the physiological relevance of this proposed Clp1p/Flp1p-dependent checkpoint is unclear because all previous studies were carried out using mutations in essential actomyosin ring components under fully restrictive conditions and thus these cells would have died regardless of the presence of the checkpoint. Here we show that delays in cytokinesis caused by minor perturbations to different components of the cytokinetic machinery, which normally cause only mild defects, become lethal when Clp1p/Flp1p is inactivated. In addition, we show that Clp1p/Flp1p does not function simply to inhibit further rounds of nuclear division, but also allows damaged actomyosin rings to be maintained to facilitate completion of cell division. Ectopic activation of the SIN significantly bypasses the requirement of Clp1p/Flp1p for G2 delay as well as for completion of cytokinesis. We conclude that the Clp1p/Flp1p-dependent cytokinesis checkpoint provides a previously unrecognized cell survival advantage when the cell division apparatus is mildly perturbed.
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Affiliation(s)
- Mithilesh Mishra
- Cell Division Laboratory, Temasek Life Sciences Laboratory, National University of Singapore, 1 Research Link, NUS, Singapore 117604, Rep. of Singapore
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Ashby MC, Ibaraki K, Henley JM. It's green outside: tracking cell surface proteins with pH-sensitive GFP. Trends Neurosci 2004; 27:257-61. [PMID: 15111007 DOI: 10.1016/j.tins.2004.03.010] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Green fluorescent protein (GFP) and mutated GFP variants have proved to be immensely powerful tools that have had a profound impact on research in biological sciences. This review considers the development, use and future implications of pH-dependent GFP variants (e.g. pHluorins). These proteins hold considerable promise for the relatively non-invasive monitoring of events such as exocytosis, endocytosis and protein surface expression in living neurons with high spatial and temporal resolution.
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Affiliation(s)
- Michael C Ashby
- MRC Centre for Synaptic Plasticity, Department of Anatomy, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
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Hausmann S, Erdjument-Bromage H, Shuman S. Schizosaccharomyces pombe Carboxyl-terminal Domain (CTD) Phosphatase Fcp1. J Biol Chem 2004; 279:10892-900. [PMID: 14701811 DOI: 10.1074/jbc.m312513200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Schizosaccharomyces pombe Fcp1 is an essential protein serine phosphatase that preferentially dephosphorylates Ser(2) of the RNA polymerase II C-terminal domain (CTD) heptad repeat Y(1)S(2)P(3)T(4)S(5)P(6)S(7). Here we show that: (i) Fcp1 acts distributively during the hydrolysis of substrates containing tandem Ser(2)-PO(4) heptads; (ii) the minimal optimal CTD substrate for Fcp1 is a single heptad of phasing S(5)P(6)S(7)Y(1)S(2)P(3)T(4); and (iii) single alanine mutations of flanking residues Tyr(1) or Pro(3) result in 6-fold decrements in CTD phosphatase activity. Fcp1 belongs to the DXDX(T/V) family of phosphotransferases that act via an acyl-phosphoenzyme intermediate. An alanine scan of 11 conserved positions of S. pombe Fcp1 identifies Thr(174), Tyr(237), Thr(243), and Tyr(249) as important for phosphatase activity. Structure-activity relationships at these positions were determined by introducing conservative substitutions. Our results, together with previous mutational studies, highlight a constellation of 11 amino acids that are conserved in all Fcp1 orthologs and likely comprise the active site.
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Affiliation(s)
- Stéphane Hausmann
- Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA
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Olsen KN, Budde BB, Siegumfeldt H, Rechinger KB, Jakobsen M, Ingmer H. Noninvasive measurement of bacterial intracellular pH on a single-cell level with green fluorescent protein and fluorescence ratio imaging microscopy. Appl Environ Microbiol 2002; 68:4145-7. [PMID: 12147523 PMCID: PMC123996 DOI: 10.1128/aem.68.8.4145-4147.2002] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We show that a pH-sensitive derivative of the green fluorescent protein, designated ratiometric GFP, can be used to measure intracellular pH (pHi) in both gram-positive and gram-negative bacterial cells. In cells expressing ratiometric GFP, the excitation ratio (fluorescence intensity at 410 and 430 nm) is correlated to the pHi, allowing fast and noninvasive determination of pHi that is ideally suited for direct analysis of individual bacterial cells present in complex environments.
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Affiliation(s)
- Katja N Olsen
- Department of Veterinary Microbiology, The Royal Veterinary and Agricultural University, DK-1870 Frederiksberg C, Denmark
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