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Kreida S, Roche JV, Missel JW, Al-Jubair T, Hagströmer CJ, Wittenbecher V, Linse S, Gourdon P, Törnroth-Horsefield S. The role of phosphorylation in calmodulin-mediated gating of human AQP0. Biochem J 2024; 481:17-32. [PMID: 38032258 PMCID: PMC10903448 DOI: 10.1042/bcj20230158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 11/17/2023] [Accepted: 11/30/2023] [Indexed: 12/01/2023]
Abstract
Aquaporin-0 (AQP0) is the main water channel in the mammalian lens and is involved in accommodation and maintaining lens transparency. AQP0 binds the Ca2+-sensing protein calmodulin (CaM) and this interaction is believed to gate its water permeability by closing the water-conducting pore. Here, we express recombinant and functional human AQP0 in Pichia pastoris and investigate how phosphorylation affects the interaction with CaM in vitro as well as the CaM-dependent water permeability of AQP0 in proteoliposomes. Using microscale thermophoresis and surface plasmon resonance technology we show that the introduction of the single phospho-mimicking mutations S229D and S235D in AQP0 reduces CaM binding. In contrast, CaM interacts with S231D with similar affinity as wild type, but in a different manner. Permeability studies of wild-type AQP0 showed that the water conductance was significantly reduced by CaM in a Ca2+-dependent manner, whereas AQP0 S229D, S231D and S235D were all locked in an open state, insensitive to CaM. We propose a model in which phosphorylation of AQP0 control CaM-mediated gating in two different ways (1) phosphorylation of S229 or S235 abolishes binding (the pore remains open) and (2) phosphorylation of S231 results in CaM binding without causing pore closure, the functional role of which remains to be elucidated. Our results suggest that site-dependent phosphorylation of AQP0 dynamically controls its CaM-mediated gating. Since the level of phosphorylation increases towards the lens inner cortex, AQP0 may become insensitive to CaM-dependent gating along this axis.
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Affiliation(s)
- Stefan Kreida
- Department of Biochemistry and Structural Biology, Lund University, Lund, Sweden
| | | | - Julie Winkel Missel
- Department of Biomedical Sciences, Copenhagen University, Copenhagen, Denmark
| | - Tamim Al-Jubair
- Department of Biochemistry and Structural Biology, Lund University, Lund, Sweden
| | | | | | - Sara Linse
- Department of Biochemistry and Structural Biology, Lund University, Lund, Sweden
| | - Pontus Gourdon
- Department of Biomedical Sciences, Copenhagen University, Copenhagen, Denmark
- Department of Experimental Medical Science, Lund University, Lund, Sweden
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2
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Donaldson PJ, Petrova RS, Nair N, Chen Y, Schey KL. Regulation of water flow in the ocular lens: new roles for aquaporins. J Physiol 2023:10.1113/JP284102. [PMID: 37843390 PMCID: PMC11018719 DOI: 10.1113/jp284102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 09/28/2023] [Indexed: 10/17/2023] Open
Abstract
The ocular lens is an important determinant of overall vision quality whose refractive and transparent properties change throughout life. The lens operates an internal microcirculation system that generates circulating fluxes of ions, water and nutrients that maintain the transparency and refractive properties of the lens. This flow of water generates a substantial hydrostatic pressure gradient which is regulated by a dual feedback system that uses the mechanosensitive channels TRPV1 and TRPV4 to sense decreases and increases, respectively, in the pressure gradient. This regulation of water flow (pressure) and hence overall lens water content, sets the two key parameters, lens geometry and the gradient of refractive index, which determine the refractive properties of the lens. Here we focus on the roles played by the aquaporin family of water channels in mediating lens water fluxes, with a specific focus on AQP5 as a regulated water channel in the lens. We show that in addition to regulating the activity of ion transporters, which generate local osmotic gradients that drive lens water flow, the TRPV1/4-mediated dual feedback system also modulates the membrane trafficking of AQP5 in the anterior influx pathway and equatorial efflux zone of the lens. Since both lens pressure and AQP5-mediated water permeability (P H 2 O ${P_{{{\mathrm{H}}_{\mathrm{2}}}{\mathrm{O}}}}$ ) can be altered by changes in the tension applied to the lens surface via modulating ciliary muscle contraction we propose extrinsic modulation of lens water flow as a potential mechanism to alter the refractive properties of the lens to ensure light remains focused on the retina throughout life.
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Affiliation(s)
- Paul J. Donaldson
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Rosica S. Petrova
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Nikhil Nair
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Yadi Chen
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Kevin L. Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN, USA
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3
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Chang Y, Hawkins BA, Du JJ, Groundwater PW, Hibbs DE, Lai F. A Guide to In Silico Drug Design. Pharmaceutics 2022; 15:pharmaceutics15010049. [PMID: 36678678 PMCID: PMC9867171 DOI: 10.3390/pharmaceutics15010049] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Revised: 12/16/2022] [Accepted: 12/17/2022] [Indexed: 12/28/2022] Open
Abstract
The drug discovery process is a rocky path that is full of challenges, with the result that very few candidates progress from hit compound to a commercially available product, often due to factors, such as poor binding affinity, off-target effects, or physicochemical properties, such as solubility or stability. This process is further complicated by high research and development costs and time requirements. It is thus important to optimise every step of the process in order to maximise the chances of success. As a result of the recent advancements in computer power and technology, computer-aided drug design (CADD) has become an integral part of modern drug discovery to guide and accelerate the process. In this review, we present an overview of the important CADD methods and applications, such as in silico structure prediction, refinement, modelling and target validation, that are commonly used in this area.
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Affiliation(s)
- Yiqun Chang
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW 2006, Australia
| | - Bryson A. Hawkins
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW 2006, Australia
| | - Jonathan J. Du
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Paul W. Groundwater
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW 2006, Australia
| | - David E. Hibbs
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW 2006, Australia
| | - Felcia Lai
- Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW 2006, Australia
- Correspondence:
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4
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Insight into the Mammalian Aquaporin Interactome. Int J Mol Sci 2022; 23:ijms23179615. [PMID: 36077012 PMCID: PMC9456110 DOI: 10.3390/ijms23179615] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Revised: 08/16/2022] [Accepted: 08/22/2022] [Indexed: 01/07/2023] Open
Abstract
Aquaporins (AQPs) are a family of transmembrane water channels expressed in all living organisms. AQPs facilitate osmotically driven water flux across biological membranes and, in some cases, the movement of small molecules (such as glycerol, urea, CO2, NH3, H2O2). Protein-protein interactions play essential roles in protein regulation and function. This review provides a comprehensive overview of the current knowledge of the AQP interactomes and addresses the molecular basis and functional significance of these protein-protein interactions in health and diseases. Targeting AQP interactomes may offer new therapeutic avenues as targeting individual AQPs remains challenging despite intense efforts.
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5
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Schey KL, Gletten RB, O’Neale CVT, Wang Z, Petrova RS, Donaldson PJ. Lens Aquaporins in Health and Disease: Location is Everything! Front Physiol 2022; 13:882550. [PMID: 35514349 PMCID: PMC9062079 DOI: 10.3389/fphys.2022.882550] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 03/23/2022] [Indexed: 01/07/2023] Open
Abstract
Cataract and presbyopia are the leading cause of vision loss and impaired vision, respectively, worldwide. Changes in lens biochemistry and physiology with age are responsible for vision impairment, yet the specific molecular changes that underpin such changes are not entirely understood. In order to preserve transparency over decades of life, the lens establishes and maintains a microcirculation system (MCS) that, through spatially localized ion pumps, induces circulation of water and nutrients into (influx) and metabolites out of (outflow and efflux) the lens. Aquaporins (AQPs) are predicted to play important roles in the establishment and maintenance of local and global water flow throughout the lens. This review discusses the structure and function of lens AQPs and, importantly, their spatial localization that is likely key to proper water flow through the MCS. Moreover, age-related changes are detailed and their predicted effects on the MCS are discussed leading to an updated MCS model. Lastly, the potential therapeutic targeting of AQPs for prevention or treatment of cataract and presbyopia is discussed.
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Affiliation(s)
- Kevin L. Schey
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States,*Correspondence: Kevin L. Schey,
| | - Romell B. Gletten
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Carla V. T. O’Neale
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Zhen Wang
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Rosica S. Petrova
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Paul J. Donaldson
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
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6
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Li Z, Quan Y, Gu S, Jiang JX. Beyond the Channels: Adhesion Functions of Aquaporin 0 and Connexin 50 in Lens Development. Front Cell Dev Biol 2022; 10:866980. [PMID: 35465319 PMCID: PMC9022433 DOI: 10.3389/fcell.2022.866980] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 03/18/2022] [Indexed: 12/04/2022] Open
Abstract
Lens, an avascular tissue involved in light transmission, generates an internal microcirculatory system to promote ion and fluid circulation, thus providing nutrients to internal lens cells and excreting the waste. This unique system makes up for the lack of vasculature and distinctively maintains lens homeostasis and lens fiber cell survival through channels of connexins and other transporters. Aquaporins (AQP) and connexins (Cx) comprise the majority of channels in the lens microcirculation system and are, thus, essential for lens development and transparency. Mutations of AQPs and Cxs result in abnormal channel function and cataract formation. Interestingly, in the last decade or so, increasing evidence has emerged suggesting that in addition to their well-established channel functions, AQP0 and Cx50 play pivotal roles through channel-independent actions in lens development and transparency. Specifically, AQP0 and Cx50 have been shown to have a unique cell adhesion function that mediates lens development and transparency. Precise regulation of cell-matrix and cell-cell adhesion is necessary for cell migration, a critical process during lens development. This review will provide recent advances in basic research of cell adhesion mediated by AQP0 and Cx50.
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Affiliation(s)
- Zhen Li
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, United States
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
| | - Yumeng Quan
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, United States
| | - Sumin Gu
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, United States
| | - Jean X. Jiang
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, United States
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7
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Molecular mechanisms governing aquaporin relocalisation. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183853. [PMID: 34973181 PMCID: PMC8825993 DOI: 10.1016/j.bbamem.2021.183853] [Citation(s) in RCA: 36] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 12/20/2021] [Accepted: 12/21/2021] [Indexed: 02/07/2023]
Abstract
The aquaporins (AQPs) form a family of integral membrane proteins that facilitate the movement of water across biological membrane by osmosis, as well as facilitating the diffusion of small polar solutes. AQPs have been recognised as drug targets for a variety of disorders associated with disrupted water or solute transport, including brain oedema following stroke or trauma, epilepsy, cancer cell migration and tumour angiogenesis, metabolic disorders, and inflammation. Despite this, drug discovery for AQPs has made little progress due to a lack of reproducible high-throughput assays and difficulties with the druggability of AQP proteins. However, recent studies have suggested that targetting the trafficking of AQP proteins to the plasma membrane is a viable alternative drug target to direct inhibition of the water-conducting pore. Here we review the literature on the trafficking of mammalian AQPs with a view to highlighting potential new drug targets for a variety of conditions associated with disrupted water and solute homeostasis. Aquaporins (AQPs) form water and solute permeable pores in biological membranes. AQPs represent attractive drug targets for disorders of water/solute homeostasis. Drug discovery efforts towards pore-blocking AQP inhibitors have made little progress. AQPs are dynamically relocalised between intracellular vesicles and plasma membrane. This relocalisation represents a new target for inhibition of AQP function.
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8
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Ishida H, Vogel HJ, Conner AC, Kitchen P, Bill RM, MacDonald JA. Simultaneous binding of the N- and C-terminal cytoplasmic domains of aquaporin 4 to calmodulin. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183837. [PMID: 34890582 DOI: 10.1016/j.bbamem.2021.183837] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 10/30/2021] [Accepted: 11/30/2021] [Indexed: 10/19/2022]
Abstract
Aquaporin 4 (AQP4) is a water transporting, transmembrane channel protein that has important regulatory roles in maintaining cellular water homeostasis. Several other AQP proteins exhibit calmodulin (CaM)-binding properties, and CaM has recently been implicated in the cell surface localization of AQP4. The objective of the present study was to assess the CaM-binding properties of AQP4 in detail. Inspection of AQP4 revealed two putative CaM-binding domains (CBDs) in the cytoplasmic N- and C-terminal regions, respectively. The Ca2+-dependent CaM-binding properties of AQP4 CBD peptides were assessed using fluorescence spectroscopy, isothermal titration calorimetry, and two-dimensional 1H, 15N-HSQC NMR with 15N-labeled CaM. The N-terminal CBD of AQP4 predominantly interacted with the N-lobe of CaM with a 1:1 binding ratio and a Kd of 3.4 μM. The C-terminal AQP4 peptide interacted with both the C- and N-lobes of CaM (2:1 binding ratio; Kd1: 3.6 μM, Kd2: 113.6 μM, respectively). A recombinant AQP4 protein domain (recAQP4CT, containing the entire cytosolic C-terminal sequence) bound CaM in a 1:1 binding mode with a Kd of 6.1 μM. A ternary bridging complex could be generated with the N- and C-lobes of CaM interacting simultaneously with the N- and C-terminal CBD peptides. These data support a unique adapter protein binding mode for CaM with AQP4.
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Affiliation(s)
- Hiroaki Ishida
- Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
| | - Hans J Vogel
- Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
| | - Alex C Conner
- College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Philip Kitchen
- College of Health and Life Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK
| | - Roslyn M Bill
- College of Health and Life Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK
| | - Justin A MacDonald
- Department of Biochemistry and Molecular Biology, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4Z6, Canada.
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9
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Wagner K, Unger L, Salman MM, Kitchen P, Bill RM, Yool AJ. Signaling Mechanisms and Pharmacological Modulators Governing Diverse Aquaporin Functions in Human Health and Disease. Int J Mol Sci 2022; 23:ijms23031388. [PMID: 35163313 PMCID: PMC8836214 DOI: 10.3390/ijms23031388] [Citation(s) in RCA: 36] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 01/18/2022] [Accepted: 01/20/2022] [Indexed: 02/07/2023] Open
Abstract
The aquaporins (AQPs) are a family of small integral membrane proteins that facilitate the bidirectional transport of water across biological membranes in response to osmotic pressure gradients as well as enable the transmembrane diffusion of small neutral solutes (such as urea, glycerol, and hydrogen peroxide) and ions. AQPs are expressed throughout the human body. Here, we review their key roles in fluid homeostasis, glandular secretions, signal transduction and sensation, barrier function, immunity and inflammation, cell migration, and angiogenesis. Evidence from a wide variety of studies now supports a view of the functions of AQPs being much more complex than simply mediating the passive flow of water across biological membranes. The discovery and development of small-molecule AQP inhibitors for research use and therapeutic development will lead to new insights into the basic biology of and novel treatments for the wide range of AQP-associated disorders.
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Affiliation(s)
- Kim Wagner
- School of Biomedicine, University of Adelaide, Adelaide, SA 5005, Australia;
| | - Lucas Unger
- College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK; (L.U.); (P.K.)
| | - Mootaz M. Salman
- Department of Physiology Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, UK;
- Oxford Parkinson’s Disease Centre, University of Oxford, South Parks Road, Oxford OX1 3QX, UK
| | - Philip Kitchen
- College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK; (L.U.); (P.K.)
| | - Roslyn M. Bill
- College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK; (L.U.); (P.K.)
- Correspondence: (R.M.B.); (A.J.Y.); Tel.: +44-121-204-4274 (R.M.B.); +61-8-8313-3359 (A.J.Y.)
| | - Andrea J. Yool
- School of Biomedicine, University of Adelaide, Adelaide, SA 5005, Australia;
- Correspondence: (R.M.B.); (A.J.Y.); Tel.: +44-121-204-4274 (R.M.B.); +61-8-8313-3359 (A.J.Y.)
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10
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Salman MM, Kitchen P, Yool AJ, Bill RM. Recent breakthroughs and future directions in drugging aquaporins. Trends Pharmacol Sci 2021; 43:30-42. [PMID: 34863533 DOI: 10.1016/j.tips.2021.10.009] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 09/09/2021] [Accepted: 10/18/2021] [Indexed: 02/06/2023]
Abstract
Aquaporins facilitate the passive transport of water, solutes, or ions across biological membranes. They are implicated in diverse pathologies including brain edema following stroke or trauma, epilepsy, cancer cell migration and tumor angiogenesis, metabolic disorders, and inflammation. Despite this, there is no aquaporin-targeted drug in the clinic and aquaporins have been perceived to be intrinsically non-druggable targets. Here we challenge this idea, as viable routes to inhibition of aquaporin function have recently been identified, including targeting their regulation or their roles as channels for unexpected substrates. Identifying new drug development frameworks for conditions associated with disrupted water and solute homeostasis will meet the urgent, unmet clinical need of millions of patients for whom no pharmacological interventions are available.
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Affiliation(s)
- Mootaz M Salman
- Department of Physiology, Anatomy and Genetics, Kavli Institute for NanoScience Discovery, University of Oxford, Oxford OX1 3PT, UK; Oxford Parkinson's Disease Centre, University of Oxford, Oxford, UK.
| | - Philip Kitchen
- School of Biosciences, College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK.
| | - Andrea J Yool
- University of Adelaide, School of Biomedicine, Adelaide, South Australia 5005, Australia.
| | - Roslyn M Bill
- School of Biosciences, College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK.
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Peracchia C, Leverone Peracchia LM. Calmodulin-Connexin Partnership in Gap Junction Channel Regulation-Calmodulin-Cork Gating Model. Int J Mol Sci 2021; 22:ijms222313055. [PMID: 34884859 PMCID: PMC8658047 DOI: 10.3390/ijms222313055] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 11/27/2021] [Accepted: 11/29/2021] [Indexed: 01/19/2023] Open
Abstract
In the past four decades numerous findings have indicated that gap junction channel gating is mediated by intracellular calcium concentrations ([Ca2+i]) in the high nanomolar range via calmodulin (CaM). We have proposed a CaM-based gating model based on evidence for a direct CaM role in gating. This model is based on the following: CaM inhibitors and the inhibition of CaM expression to prevent chemical gating. A CaM mutant with higher Ca2+ sensitivity greatly increases gating sensitivity. CaM co-localizes with connexins. Connexins have high-affinity CaM-binding sites. Connexin mutants paired to wild type connexins have a higher gating sensitivity, which is eliminated by the inhibition of CaM expression. Repeated trans-junctional voltage (Vj) pulses progressively close channels by the chemical/slow gate (CaM’s N-lobe). At the single channel level, the gate closes and opens slowly with on-off fluctuations. Internally perfused crayfish axons lose gating competency but recover it by the addition of Ca-CaM to the internal perfusion solution. X-ray diffraction data demonstrate that isolated gap junctions are gated at the cytoplasmic end by a particle of the size of a CaM lobe. We have proposed two types of CaM-driven gating: “Ca-CaM-Cork” and “CaM-Cork”. In the first, the gating involves Ca2+-induced CaM activation. In the second, the gating occurs without a [Ca2+]i rise.
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12
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Hu Z, Riquelme MA, Gu S, Jiang JX. Regulation of Connexin Gap Junctions and Hemichannels by Calcium and Calcium Binding Protein Calmodulin. Int J Mol Sci 2020; 21:E8194. [PMID: 33147690 PMCID: PMC7663298 DOI: 10.3390/ijms21218194] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 10/30/2020] [Accepted: 10/31/2020] [Indexed: 12/20/2022] Open
Abstract
Connexins are the structural components of gap junctions and hemichannels that mediate the communication and exchange of small molecules between cells, and between the intracellular and extracellular environment, respectively. Connexin (Cx) 46 is predominately expressed in lens fiber cells, where they function in maintaining the homeostasis and transparency of the lens. Cx46 mutations are associated with impairment of channel function, which results in the development of congenital cataracts. Cx46 gap junctions and hemichannels are closely regulated by multiple mechanisms. Key regulators of Cx46 channel function include Ca2+ and calmodulin (CaM). Ca2+ plays an essential role in lens homeostasis, and its dysregulation causes cataracts. Ca2+ associated CaM is a well-established inhibitor of gap junction coupling. Recent studies suggest that elevated intracellular Ca2+ activates Cx hemichannels in lens fiber cells and Cx46 directly interacts with CaM. A Cx46 site mutation (Cx46-G143R), which is associated with congenital Coppock cataracts, shows an increased Cx46-CaM interaction and this interaction is insensitive to Ca2+, given that depletion of Ca2+ reduces the interaction between CaM and wild-type Cx46. Moreover, inhibition of CaM function greatly reduces the hemichannel activity in the Cx46 G143R mutant. These research findings suggest a new regulatory mechanism by which enhanced association of Cx46 with CaM leads to the increase in hemichannel activity and dysregulation may lead to cataract development. In this review, we will first discuss the involvement of Ca2+/CaM in lens homeostasis and pathology, and follow by providing a general overview of Ca2+/CaM in the regulation of Cx46 gap junctions. We discuss the most recent studies concerning the molecular mechanism of Ca2+/CaM in regulating Cx46 hemichannels. Finally, we will offer perspectives of the impacts of Ca2+/CaM and dysregulation on Cx46 channels and vice versa.
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Affiliation(s)
- Zhengping Hu
- Schepens Eye Research Institute of Massachusetts Eye and Ear, Boston, MA 02114, USA;
- Department of Ophthalmology, Harvard Medical School, Boston, MA 02114, USA
| | - Manuel A. Riquelme
- Departments of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX 78229, USA; (M.A.R.); (S.G.)
| | - Sumin Gu
- Departments of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX 78229, USA; (M.A.R.); (S.G.)
| | - Jean X. Jiang
- Departments of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX 78229, USA; (M.A.R.); (S.G.)
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13
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Pérez-Mejías G, Velázquez-Cruz A, Guerra-Castellano A, Baños-Jaime B, Díaz-Quintana A, González-Arzola K, Ángel De la Rosa M, Díaz-Moreno I. Exploring protein phosphorylation by combining computational approaches and biochemical methods. Comput Struct Biotechnol J 2020; 18:1852-1863. [PMID: 32728408 PMCID: PMC7369424 DOI: 10.1016/j.csbj.2020.06.043] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 06/29/2020] [Accepted: 06/30/2020] [Indexed: 12/14/2022] Open
Abstract
Post-translational modifications of proteins expand their functional diversity, regulating the response of cells to a variety of stimuli. Among these modifications, phosphorylation is the most ubiquitous and plays a prominent role in cell signaling. The addition of a phosphate often affects the function of a protein by altering its structure and dynamics. However, these alterations are often difficult to study and the functional and structural implications remain unresolved. New approaches are emerging to overcome common obstacles related to the production and manipulation of these samples. Here, we summarize the available methods for phosphoprotein purification and phosphomimetic engineering, highlighting the advantages and disadvantages of each. We propose a general workflow for protein phosphorylation analysis combining computational and biochemical approaches, building on recent advances that enable user-friendly and easy-to-access Molecular Dynamics simulations. We hope this innovative workflow will inform the best experimental approach to explore such post-translational modifications. We have applied this workflow to two different human protein models: the hemeprotein cytochrome c and the RNA binding protein HuR. Our results illustrate the usefulness of Molecular Dynamics as a decision-making tool to design the most appropriate phosphomimetic variant.
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Affiliation(s)
- Gonzalo Pérez-Mejías
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Alejandro Velázquez-Cruz
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Alejandra Guerra-Castellano
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Blanca Baños-Jaime
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Antonio Díaz-Quintana
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Katiuska González-Arzola
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Miguel Ángel De la Rosa
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Irene Díaz-Moreno
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
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14
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Peracchia C. Calmodulin-Mediated Regulation of Gap Junction Channels. Int J Mol Sci 2020; 21:E485. [PMID: 31940951 PMCID: PMC7014422 DOI: 10.3390/ijms21020485] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 01/03/2020] [Accepted: 01/06/2020] [Indexed: 12/25/2022] Open
Abstract
Evidence that neighboring cells uncouple from each other as one dies surfaced in the late 19th century, but it took almost a century for scientists to start understanding the uncoupling mechanism (chemical gating). The role of cytosolic free calcium (Ca2+i) in cell-cell channel gating was first reported in the mid-sixties. In these studies, only micromolar [Ca2+]i were believed to affect gating-concentrations reachable only in cell death, which would discard Ca2+i as a fine modulator of cell coupling. More recently, however, numerous researchers, including us, have reported the effectiveness of nanomolar [Ca2+]i. Since connexins do not have high-affinity calcium sites, the effectiveness of nanomolar [Ca2+]i suggests the role of Ca-modulated proteins, with calmodulin (CaM) being most obvious. Indeed, in 1981 we first reported that a CaM-inhibitor prevents chemical gating. Since then, the CaM role in gating has been confirmed by studies that tested it with a variety of approaches such as treatments with CaM-inhibitors, inhibition of CaM expression, expression of CaM mutants, immunofluorescent co-localization of CaM and gap junctions, and binding of CaM to peptides mimicking connexin domains identified as CaM targets. Our gating model envisions Ca2+-CaM to directly gate the channels by acting as a plug ("Cork" gating model), and probably also by affecting connexin conformation.
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Affiliation(s)
- Camillo Peracchia
- Department of Pharmacology and Physiology, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, USA
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15
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Schey KL, Wang Z, Friedrich MG, Garland DL, Truscott RJW. Spatiotemporal changes in the human lens proteome: Critical insights into long-lived proteins. Prog Retin Eye Res 2019; 76:100802. [PMID: 31704338 DOI: 10.1016/j.preteyeres.2019.100802] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 10/24/2019] [Accepted: 10/30/2019] [Indexed: 12/15/2022]
Abstract
The ocular lens is a unique tissue that contains an age gradient of cells and proteins ranging from newly differentiated cells containing newly synthesized proteins to cells and proteins that are as old as the organism. Thus, the ocular lens is an excellent model for studying long-lived proteins (LLPs) and the effects of aging and post-translational modifications on protein structure and function. Given the architecture of the lens, with young fiber cells in the outer cortex and the oldest cells in the lens nucleus, spatially-resolved studies provide information on age-specific protein changes. In this review, experimental strategies and proteomic methods that have been used to examine age-related and cataract-specific changes to the human lens proteome are described. Measured spatio-temporal changes in the human lens proteome are summarized and reveal a highly consistent, time-dependent set of modifications observed in transparent human lenses. Such measurements have led to the discovery of cataract-specific modifications and the realization that many animal systems are unsuitable to study many of these modifications. Mechanisms of protein modifications such as deamidation, racemization, truncation, and protein-protein crosslinking are presented and the implications of such mechanisms for other long-lived proteins in other tissues are discussed in the context of age-related neurological diseases. A comprehensive understanding of LLP modifications will enhance our ability to develop new therapies for the delay, prevention or reversal of age-related diseases.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt University, USA.
| | - Zhen Wang
- Department of Biochemistry, Vanderbilt University, USA
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
| | | | - Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
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16
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Varadaraj K, Kumari S. Deletion of Seventeen Amino Acids at the C-Terminal End of Aquaporin 0 Causes Distortion Aberration and Cataract in the Lenses of AQP0ΔC/ΔC Mice. Invest Ophthalmol Vis Sci 2019; 60:858-867. [PMID: 30821811 PMCID: PMC6397018 DOI: 10.1167/iovs.18-26378] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Purpose Investigate the effects of the absence of 17 amino acids at the C-terminal end of Aquaporin 0 (AQP0) on lens transparency, focusing property, and homeostasis. Methods A knockin (KI) mouse model (AQP0ΔC/ΔC) was developed to express AQP0 only as the end-cleaved form in the lens. For this, AQP0 was genetically engineered as C-terminally end-cleaved with amino acids 1 to 246, instead of the full length 1 to 263 of the wild type (WT). After verifying the KI integration into the genome and its expression, the mouse model was bred for several generations. AQP0 KI homozygous (AQP0ΔC/ΔC) and heterozygous (AQP0+/ΔC) lenses were imaged and analyzed at different developmental stages for transparency. Correspondingly, aberrations in the lens were characterized using the standard metal grid focusing method. Data were compared with age-matched WT, AQP0 knockout (AQP0-/-), and AQP0 heterozygous (AQP0+/-) lenses. Results AQP0ΔC/ΔC lenses were transparent throughout the embryonic development and until postnatal day 15 (P15) in contrast to age-matched AQP0-/- lenses, which developed cataract at embryonic stage itself. However, there was distortion aberration in AQP0ΔC/ΔC lens at P5; after P15, cataract began to develop and progressed faster surpassing that of age-matched AQP0-/- lenses. AQP0+/ΔC lenses were transparent even at the age of 1 year in contrast to AQP0+/- lenses; however, there was distortion aberration starting at P15. Conclusions A specific distribution profile of intact and end-cleaved AQP0 from the outer cortex to the inner nucleus is required in the lens for establishing refractive index gradient to enable proper focusing without aberrations and for maintaining transparency.
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Affiliation(s)
- Kulandaiappan Varadaraj
- Department of Physiology and Biophysics, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York, United States
| | - Sindhu Kumari
- Department of Physiology and Biophysics, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York, United States
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17
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Hollingsworth SA, Dror RO. Molecular Dynamics Simulation for All. Neuron 2019; 99:1129-1143. [PMID: 30236283 DOI: 10.1016/j.neuron.2018.08.011] [Citation(s) in RCA: 910] [Impact Index Per Article: 182.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 07/17/2018] [Accepted: 08/07/2018] [Indexed: 12/12/2022]
Abstract
The impact of molecular dynamics (MD) simulations in molecular biology and drug discovery has expanded dramatically in recent years. These simulations capture the behavior of proteins and other biomolecules in full atomic detail and at very fine temporal resolution. Major improvements in simulation speed, accuracy, and accessibility, together with the proliferation of experimental structural data, have increased the appeal of biomolecular simulation to experimentalists-a trend particularly noticeable in, although certainly not limited to, neuroscience. Simulations have proven valuable in deciphering functional mechanisms of proteins and other biomolecules, in uncovering the structural basis for disease, and in the design and optimization of small molecules, peptides, and proteins. Here we describe, in practical terms, the types of information MD simulations can provide and the ways in which they typically motivate further experimental work.
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Affiliation(s)
- Scott A Hollingsworth
- Department of Computer Science, Stanford University, Stanford, CA 94305, USA; Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA 94305, USA
| | - Ron O Dror
- Department of Computer Science, Stanford University, Stanford, CA 94305, USA; Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA 94305, USA.
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18
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Cooperativity and allostery in aquaporin 0 regulation by Ca 2. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1861:988-996. [PMID: 30802427 DOI: 10.1016/j.bbamem.2019.02.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 02/18/2019] [Accepted: 02/20/2019] [Indexed: 11/21/2022]
Abstract
Aquaporin 0 (AQP0) is essential for eye lens homeostasis as is regulation of its water permeability by Ca2+, which occurs through interactions with calmodulin (CaM), but the underlying molecular mechanisms are not well understood. Here, we use molecular dynamics (MD) simulations on the microsecond timescale under an osmotic gradient to explicitly model water permeation through the AQP0 channel. To identify any structural features that are specific to water permeation through AQP0, we also performed simulations of aquaporin 1 (AQP1) and a pure mixed lipid bilayer under the same conditions. The relative single-channel water osmotic permeability coefficients (pf) calculated from all of our simulations are in reasonable agreement with experiment. Our simulations allowed us to characterize the dynamics of the key structural elements that modulate the diffusion of water single-files through the AQP0 and AQP1 pores. We find that CaM binding influences the collective dynamics of the whole AQP0 tetramer, promoting the closing of both the extracellular and intracellular gates by inducing cooperativity between neighboring subunits.
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19
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Hall JE, Freites JA, Tobias DJ. Experimental and Simulation Studies of Aquaporin 0 Water Permeability and Regulation. Chem Rev 2019; 119:6015-6039. [PMID: 31026155 DOI: 10.1021/acs.chemrev.9b00106] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
We begin with the history of aquaporin zero (AQP0), the most prevalent membrane protein in the eye lens, from the early days when AQP0 was a protein of unknown function known as Major Intrinsic Protein 26. We progress through its joining the aquaporin family as a water channel in its own right and discuss how regulation of its water permeability by pH and calcium came to be discovered experimentally and linked to lens homeostasis and development. We review the development of molecular dynamics (MD) simulations of lipid bilayers and membrane proteins, including aquaporins, with an emphasis on simulation studies that have elucidated the mechanisms of water conduction, selectivity, and proton exclusion by aquaporins in general. We also review experimental and theoretical progress toward understanding why mammalian AQP0 has a lower water permeability than other aquaporins and the evolution of our present understanding of how its water permeability is regulated by pH and calcium. Finally, we discuss how MD simulations have elucidated the nature of lipid interactions with AQP0.
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20
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Vorontsova I, Gehring I, Hall JE, Schilling TF. Aqp0a Regulates Suture Stability in the Zebrafish Lens. Invest Ophthalmol Vis Sci 2019; 59:2869-2879. [PMID: 30025131 PMCID: PMC5987579 DOI: 10.1167/iovs.18-24044] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Purpose To investigate the roles of Aquaporin 0a (Aqp0a) and Aqp0b in zebrafish lens development and transparency. Methods CRISPR/Cas9 gene editing was used to generate loss-of-function deletions in zebrafish aqp0a and/or aqp0b. Wild type (WT), single mutant, and double mutant lenses were analyzed from embryonic to adult stages. Lens transparency, morphology, and growth were assessed. Immunohistochemistry was used to map protein localization as well as to assess tissue organization and distribution of cell nuclei. Results aqp0a−/− and/or aqp0b−/− cause embryonic cataracts with variable penetrance. While lenses of single mutants of either gene recover transparency in juveniles, double mutants consistently form dense cataracts that persist in adults, indicating partially redundant functions. Double mutants also reveal redundant Aqp0 functions in lens growth. The nucleus of WT lenses moves from the anterior pole to the lens center with age. In aqp0a−/− mutants, the nucleus fails to centralize as it does in WT or aqp0b−/− lenses, and in double mutant lenses there is no consistent lens nuclear position. In addition, the anterior sutures of aqp0a−/−, but not aqp0b−/− mutants, are unstable resulting in failure of suture maintenance at older stages and anterior polar opacity. Conclusions. Zebrafish Aqp0s have partially redundant functions, but only Aqp0a promotes suture stability, which directs the lens nucleus to centralize, failure of which results in anterior polar opacity. These studies support the hypothesis that the two Aqp0s subfunctionalized during fish evolution and that Aqp0-dependent maintenance of the anterior suture is essential for lens transparency.
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Affiliation(s)
- Irene Vorontsova
- Department of Physiology and Biophysics, University of California, Irvine, California, United States.,Department of Developmental and Cell Biology, University of California, Irvine, California, United States
| | - Ines Gehring
- Department of Developmental and Cell Biology, University of California, Irvine, California, United States
| | - James E Hall
- Department of Physiology and Biophysics, University of California, Irvine, California, United States
| | - Thomas F Schilling
- Department of Developmental and Cell Biology, University of California, Irvine, California, United States
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21
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Increasing Salt Rejection of Polybenzimidazole Nanofiltration Membranes via the Addition of Immobilized and Aligned Aquaporins. Processes (Basel) 2019; 7. [PMID: 31179235 PMCID: PMC6550480 DOI: 10.3390/pr7020076] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Aquaporins are water channel proteins in cell membrane, highly specific for water molecules while restricting the passage of contaminants and small molecules, such as urea and boric acid. Cysteine functional groups were installed on aquaporin Z for covalent attachment to the polymer membrane matrix so that the proteins could be immobilized to the membranes and aligned in the direction of the flow. Depth profiling using x-ray photoelectron spectrometer (XPS) analysis showed the presence of functional groups corresponding to aquaporin Z modified with cysteine (Aqp-SH). Aqp-SH modified membranes showed a higher salt rejection as compared to unmodified membranes. For 2 M NaCl and CaCl2 solutions, the rejection obtained from Aqp-SH membranes was 49.3 ± 7.5% and 59.1 ± 5.1%. On the other hand, the rejections obtained for 2 M NaCl and CaCl2 solutions from unmodified membranes were 0.8 ± 0.4% and 1.3 ± 0.2% respectively. Furthermore, Aqp-SH membranes did not show a significant decrease in salt rejection with increasing feed concentrations, as was observed with other membranes. Through simulation studies, it was determined that there was approximately 24% capping of membrane pores by dispersed aquaporins.
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22
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Nesverova V, Törnroth-Horsefield S. Phosphorylation-Dependent Regulation of Mammalian Aquaporins. Cells 2019; 8:cells8020082. [PMID: 30678081 PMCID: PMC6406877 DOI: 10.3390/cells8020082] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 01/17/2019] [Accepted: 01/21/2019] [Indexed: 12/26/2022] Open
Abstract
Water homeostasis is fundamental for cell survival. Transport of water across cellular membranes is governed by aquaporins—tetrameric integral membrane channels that are highly conserved throughout the prokaryotic and eukaryotic kingdoms. In eukaryotes, specific regulation of these channels is required and is most commonly carried out by shuttling the protein between cellular compartments (trafficking) or by opening and closing the channel (gating). Structural and functional studies have revealed phosphorylation as a ubiquitous mechanism in aquaporin regulation by both regulatory processes. In this review we summarize what is currently known about the phosphorylation-dependent regulation of mammalian aquaporins. Focusing on the water-specific aquaporins (AQP0–AQP5), we discuss how gating and trafficking are controlled by phosphorylation and how phosphorylation affects the binding of aquaporins to regulatory proteins, thereby highlighting structural details and dissecting the contribution of individual phosphorylated residues when possible. Our aim is to provide an overview of the mechanisms behind how aquaporin phosphorylation controls cellular water balance and to identify key areas where further studies are needed.
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Affiliation(s)
- Veronika Nesverova
- Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, Box 124, 221 00 Lund, Sweden.
| | - Susanna Törnroth-Horsefield
- Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, Box 124, 221 00 Lund, Sweden.
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23
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Ozu M, Galizia L, Acuña C, Amodeo G. Aquaporins: More Than Functional Monomers in a Tetrameric Arrangement. Cells 2018; 7:E209. [PMID: 30423856 PMCID: PMC6262540 DOI: 10.3390/cells7110209] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Revised: 10/27/2018] [Accepted: 11/07/2018] [Indexed: 12/11/2022] Open
Abstract
Aquaporins (AQPs) function as tetrameric structures in which each monomer has its own permeable pathway. The combination of structural biology, molecular dynamics simulations, and experimental approaches has contributed to improve our knowledge of how protein conformational changes can challenge its transport capacity, rapidly altering the membrane permeability. This review is focused on evidence that highlights the functional relationship between the monomers and the tetramer. In this sense, we address AQP permeation capacity as well as regulatory mechanisms that affect the monomer, the tetramer, or tetramers combined in complex structures. We therefore explore: (i) water permeation and recent evidence on ion permeation, including the permeation pathway controversy-each monomer versus the central pore of the tetramer-and (ii) regulatory mechanisms that cannot be attributed to independent monomers. In particular, we discuss channel gating and AQPs that sense membrane tension. For the latter we propose a possible mechanism that includes the monomer (slight changes of pore shape, the number of possible H-bonds between water molecules and pore-lining residues) and the tetramer (interactions among monomers and a positive cooperative effect).
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Affiliation(s)
- Marcelo Ozu
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EGA, Argentina.
- Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires C1428EGA CABA, Argentina.
| | - Luciano Galizia
- Instituto de investigaciones Médicas A. Lanari, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires C1427ARO, Argentina.
- Consejo Nacional de Investigaciones Científicas y Técnicas, Laboratorio de Canales Iónicos, Instituto de Investigaciones Médicas (IDIM), Universidad de Buenos Aires, Buenos Aires C1427ARO, Argentina.
| | - Cynthia Acuña
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EGA, Argentina.
- Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires C1428EGA CABA, Argentina.
| | - Gabriela Amodeo
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EGA, Argentina.
- Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires C1428EGA CABA, Argentina.
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24
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Schey KL, Petrova RS, Gletten RB, Donaldson PJ. The Role of Aquaporins in Ocular Lens Homeostasis. Int J Mol Sci 2017; 18:E2693. [PMID: 29231874 PMCID: PMC5751294 DOI: 10.3390/ijms18122693] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 12/08/2017] [Accepted: 12/08/2017] [Indexed: 12/13/2022] Open
Abstract
Abstract: Aquaporins (AQPs), by playing essential roles in the maintenance of ocular lens homeostasis, contribute to the establishment and maintenance of the overall optical properties of the lens over many decades of life. Three aquaporins, AQP0, AQP1 and AQP5, each with distinctly different functional properties, are abundantly and differentially expressed in the different regions of the ocular lens. Furthermore, the diversity of AQP functionality is increased in the absence of protein turnover by age-related modifications to lens AQPs that are proposed to alter AQP function in the different regions of the lens. These regional differences in AQP functionality are proposed to contribute to the generation and directionality of the lens internal microcirculation; a system of circulating ionic and fluid fluxes that delivers nutrients to and removes wastes from the lens faster than could be achieved by passive diffusion alone. In this review, we present how regional differences in lens AQP isoforms potentially contribute to this microcirculation system by highlighting current areas of investigation and emphasizing areas where future work is required.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA.
| | - Rosica S Petrova
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Centre, University of Auckland, Auckland 1023, New Zealand.
| | - Romell B Gletten
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA.
| | - Paul J Donaldson
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Centre, University of Auckland, Auckland 1023, New Zealand.
- School of Optometry and Vison Sciences, New Zealand National Eye Centre, University of Auckland, Auckland 1023, New Zealand.
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