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Cheng C. Tissue, cellular, and molecular level determinants for eye lens stiffness and elasticity. FRONTIERS IN OPHTHALMOLOGY 2024; 4:1456474. [PMID: 39176256 PMCID: PMC11339033 DOI: 10.3389/fopht.2024.1456474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/28/2024] [Accepted: 07/26/2024] [Indexed: 08/24/2024]
Abstract
The eye lens is a transparent, ellipsoid tissue in the anterior chamber that is required for the fine focusing of light onto the retina to transmit a clear image. The focusing function of the lens is tied to tissue transparency, refractive index, and biomechanical properties. The stiffness and elasticity or resilience of the human lens allows for shape changes during accommodation to focus light from objects near and far. It has long been hypothesized that changes in lens biomechanical properties with age lead to the loss of accommodative ability and the need for reading glasses with age. However, the cellular and molecular mechanisms that influence lens biomechanical properties and/or change with age remain unclear. Studies of lens stiffness and resilience in mouse models with genetic defects or at advanced age inform us of the cytoskeletal, structural, and morphometric parameters that are important for biomechanical stability. In this review, we will explore whether: 1) tissue level changes, including the capsule, lens volume, and nucleus volume, 2) cellular level alterations, including cell packing, suture organization, and complex membrane interdigitations, and 3) molecular scale modifications, including the F-actin and intermediate filament networks, protein modifications, lipids in the cell membrane, and hydrostatic pressure, influence overall lens biomechanical properties.
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Affiliation(s)
- Catherine Cheng
- School of Optometry and Vision Science Program, Indiana University, Bloomington, IN, United States
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2
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Yu Y, Qiao Y, Ye Y, Luo C, Yao K. A novel single-base deletional mutation of MIP impairs protein distribution and cell-to-cell adhesion in autosomal dominant cataracts in a Chinese family. Am J Med Genet A 2024; 194:e63504. [PMID: 38153133 DOI: 10.1002/ajmg.a.63504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Revised: 11/24/2023] [Accepted: 12/01/2023] [Indexed: 12/29/2023]
Abstract
Congenital cataracts are the leading cause of irreversible visual disability in children, and genetic factors play an important role in their development. In this study, targeted exome sequencing revealed a novel single-base deletional mutation of MIP (c.301delG; p.Ala101Profs*16) segregated with congenital punctate cataract in a Chinese family. The hydrophobic properties, and secondary and tertiary structures for truncated MIP were predicted to affect the function of protein by bioinformatics analysis. When MIP-WT and MIP-Ala101fs expression constructs were singly transfected into HeLa cells, it was found that the mRNA level showed no significant difference, while the protein level of the mutant was remarkably reduced compared to that of the wild-type MIP. Immunofluorescence images showed that the MIP-WT was principally localized to the plasma membrane, whereas the MIP-Ala101fs protein was aberrantly trapped in the cytoplasm. Furthermore, the cell-to-cell adhesion capability and the cell-to-cell communication property were both significantly reduced for MIP-Ala101fs compared to the MIP-WT (all *p < 0.05). This is the first report of the c.301delG mutation in the MIP gene associated with autosomal dominant congenital cataracts. We propose that the cataract is caused by the decreased protein expression and reduced cell-to-cell adhesion by the mutant MIP. The impaired trafficking or instability of the mutant protein, as well as compromised intercellular communication is probably a concurrent result of the mutation. The results expand the genetic and phenotypic spectra of MIP and help to better understand the molecular basis of congenital cataracts.
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Affiliation(s)
- Yinhui Yu
- Eye Center, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Zhejiang Provincial Key Laboratory of Ophthalmology, Zhejiang Provincial Clinical Research Center for Eye Diseases, Zhejiang Provincial Engineering Institute on Eye Diseases, Hangzhou, China
| | - Yue Qiao
- Eye Center, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Zhejiang Provincial Key Laboratory of Ophthalmology, Zhejiang Provincial Clinical Research Center for Eye Diseases, Zhejiang Provincial Engineering Institute on Eye Diseases, Hangzhou, China
| | - Yang Ye
- Eye Center, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Zhejiang Provincial Key Laboratory of Ophthalmology, Zhejiang Provincial Clinical Research Center for Eye Diseases, Zhejiang Provincial Engineering Institute on Eye Diseases, Hangzhou, China
| | - Chenqi Luo
- Eye Center, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Zhejiang Provincial Key Laboratory of Ophthalmology, Zhejiang Provincial Clinical Research Center for Eye Diseases, Zhejiang Provincial Engineering Institute on Eye Diseases, Hangzhou, China
| | - Ke Yao
- Eye Center, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Zhejiang Provincial Key Laboratory of Ophthalmology, Zhejiang Provincial Clinical Research Center for Eye Diseases, Zhejiang Provincial Engineering Institute on Eye Diseases, Hangzhou, China
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Aquaporins and Ion Channels as Dual Targets in the Design of Novel Glioblastoma Therapeutics to Limit Invasiveness. Cancers (Basel) 2023; 15:cancers15030849. [PMID: 36765806 PMCID: PMC9913334 DOI: 10.3390/cancers15030849] [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: 12/23/2022] [Revised: 01/20/2023] [Accepted: 01/28/2023] [Indexed: 01/31/2023] Open
Abstract
Current therapies for Glioblastoma multiforme (GBM) focus on eradicating primary tumors using radiotherapy, chemotherapy and surgical resection, but have limited success in controlling the invasive spread of glioma cells into a healthy brain, the major factor driving short survival times for patients post-diagnosis. Transcriptomic analyses of GBM biopsies reveal clusters of membrane signaling proteins that in combination serve as robust prognostic indicators, including aquaporins and ion channels, which are upregulated in GBM and implicated in enhanced glioblastoma motility. Accumulating evidence supports our proposal that the concurrent pharmacological targeting of selected subclasses of aquaporins and ion channels could impede glioblastoma invasiveness by impairing key cellular motility pathways. Optimal sets of channels to be selected as targets for combined therapies could be tailored to the GBM cancer subtype, taking advantage of differences in patterns of expression between channels that are characteristic of GBM subtypes, as well as distinguishing them from non-cancerous brain cells such as neurons and glia. Focusing agents on a unique channel fingerprint in GBM would further allow combined agents to be administered at near threshold doses, potentially reducing off-target toxicity. Adjunct therapies which confine GBM tumors to their primary sites during clinical treatments would offer profound advantages for treatment efficacy.
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Ozu M, Alvear-Arias JJ, Fernandez M, Caviglia A, Peña-Pichicoi A, Carrillo C, Carmona E, Otero-Gonzalez A, Garate JA, Amodeo G, Gonzalez C. Aquaporin Gating: A New Twist to Unravel Permeation through Water Channels. Int J Mol Sci 2022; 23:12317. [PMID: 36293170 PMCID: PMC9604103 DOI: 10.3390/ijms232012317] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2022] [Revised: 09/30/2022] [Accepted: 10/05/2022] [Indexed: 11/17/2022] Open
Abstract
Aquaporins (AQPs) are small transmembrane tetrameric proteins that facilitate water, solute and gas exchange. Their presence has been extensively reported in the biological membranes of almost all living organisms. Although their discovery is much more recent than ion transport systems, different biophysical approaches have contributed to confirm that permeation through each monomer is consistent with closed and open states, introducing the term gating mechanism into the field. The study of AQPs in their native membrane or overexpressed in heterologous systems have experimentally demonstrated that water membrane permeability can be reversibly modified in response to specific modulators. For some regulation mechanisms, such as pH changes, evidence for gating is also supported by high-resolution structures of the water channel in different configurations as well as molecular dynamics simulation. Both experimental and simulation approaches sustain that the rearrangement of conserved residues contributes to occlude the cavity of the channel restricting water permeation. Interestingly, specific charged and conserved residues are present in the environment of the pore and, thus, the tetrameric structure can be subjected to alter the positions of these charges to sustain gating. Thus, is it possible to explore whether the displacement of these charges (gating current) leads to conformational changes? To our knowledge, this question has not yet been addressed at all. In this review, we intend to analyze the suitability of this proposal for the first time.
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Affiliation(s)
- Marcelo Ozu
- Department of Biodiversity and Experimental Biology, Faculty of Exact & Natural Sciences, University of Buenos Aires, Buenos Aires C1053, Argentina
- CONICET—Institute of Biodiversity and Experimental and Applied Biology CONICET (IBBEA), University of Buenos Aires, Buenos Aires C1053, Argentina
| | - Juan José Alvear-Arias
- Interdisciplinary Center of Neurosciences of Valparaiso, University of Valparaiso, CINV, Valparaíso 2360102, Chile
- Millennium Nucleus in NanoBioPhysics, Scientific and Technologic Center of Excellence of Science and Life, Santiago 7750000, Chile
| | - Miguel Fernandez
- Interdisciplinary Center of Neurosciences of Valparaiso, University of Valparaiso, CINV, Valparaíso 2360102, Chile
- Millennium Nucleus in NanoBioPhysics, Scientific and Technologic Center of Excellence of Science and Life, Santiago 7750000, Chile
| | - Agustín Caviglia
- CONICET—Institute of Biodiversity and Experimental and Applied Biology CONICET (IBBEA), University of Buenos Aires, Buenos Aires C1053, Argentina
| | - Antonio Peña-Pichicoi
- Interdisciplinary Center of Neurosciences of Valparaiso, University of Valparaiso, CINV, Valparaíso 2360102, Chile
- Millennium Nucleus in NanoBioPhysics, Scientific and Technologic Center of Excellence of Science and Life, Santiago 7750000, Chile
| | - Christian Carrillo
- Interdisciplinary Center of Neurosciences of Valparaiso, University of Valparaiso, CINV, Valparaíso 2360102, Chile
- Millennium Nucleus in NanoBioPhysics, Scientific and Technologic Center of Excellence of Science and Life, Santiago 7750000, Chile
| | - Emerson Carmona
- Cell Physiology and Molecular Biophysics Department and the Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Anselmo Otero-Gonzalez
- Center of Protein Study, Faculty of Biology, University of Havana, La Habana 10400, Cuba
| | - José Antonio Garate
- Interdisciplinary Center of Neurosciences of Valparaiso, University of Valparaiso, CINV, Valparaíso 2360102, Chile
- Millennium Nucleus in NanoBioPhysics, Scientific and Technologic Center of Excellence of Science and Life, Santiago 7750000, Chile
- Faculty of Engineering and Technology, University of San Sebastian, Santiago 8420524, Chile
| | - Gabriela Amodeo
- Department of Biodiversity and Experimental Biology, Faculty of Exact & Natural Sciences, University of Buenos Aires, Buenos Aires C1053, Argentina
- CONICET—Institute of Biodiversity and Experimental and Applied Biology CONICET (IBBEA), University of Buenos Aires, Buenos Aires C1053, Argentina
| | - Carlos Gonzalez
- Interdisciplinary Center of Neurosciences of Valparaiso, University of Valparaiso, CINV, Valparaíso 2360102, Chile
- Millennium Nucleus in NanoBioPhysics, Scientific and Technologic Center of Excellence of Science and Life, Santiago 7750000, Chile
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL 33136, USA
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Cheng C, Gao J, Sun X, Mathias RT. Eph-ephrin Signaling Affects Eye Lens Fiber Cell Intracellular Voltage and Membrane Conductance. Front Physiol 2021; 12:772276. [PMID: 34899394 PMCID: PMC8656704 DOI: 10.3389/fphys.2021.772276] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 10/27/2021] [Indexed: 01/07/2023] Open
Abstract
The avascular eye lens generates its own microcirculation that is required for maintaining lifelong lens transparency. The microcirculation relies on sodium ion flux, an extensive network of gap junction (GJ) plaques between lens fiber cells and transmembrane water channels. Disruption of connexin proteins, the building blocks of GJs, or aquaporins, which make up water and adhesion channels, lead to lens opacification or cataracts. Recent studies have revealed that disruption of Eph-ephrin signaling, in particular the receptor EphA2 and the ligand ephrin-A5, in humans and mice lead to congenital and age-related cataracts. We investigated whether changes in lens transparency in EphA2 or ephrin-A5 knockout (–/–) mice is related to changes in GJ coupling and lens fluid and ion homeostasis. Immunostaining revealed changes in connexin 50 (Cx50) subcellular localization in EphA2–/– peripheral lens fibers and alteration in aquaporin 0 (Aqp0) staining patterns in ephrin-A5–/– and EphA2–/– inner mature fiber cells. Surprisingly, there was no obvious change in GJ coupling in knockout lenses. However, there were changes in fiber cell membrane conductance and intracellular voltage in knockout lenses from 3-month-old mice. These knockout lenses displayed decreased conductance of mature fiber membranes and were hyperpolarized compared to control lenses. This is the first demonstration that the membrane conductance of lens fibers can be regulated. Together these data suggest that EphA2 may be needed for normal Cx50 localization to the cell membrane and that conductance of lens fiber cells requires normal Eph-ephrin signaling and water channel localization.
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Affiliation(s)
- Catherine Cheng
- School of Optometry and Vision Science Program, Indiana University, Bloomington, IN, United States
| | - Junyuan Gao
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY, United States
| | - Xiurong Sun
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY, United States
| | - Richard T Mathias
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY, United States
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Abarghooi Kahaki F, Monzavi S, Bamehr H, Bandani E, Payandeh Z, Jahangiri A, Khalili S. Expression and Purification of Membrane Proteins in Different Hosts. Int J Pept Res Ther 2020. [DOI: 10.1007/s10989-019-10009-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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7
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Hirschi S, Kalbermatter D, Ucurum Z, Fotiadis D. Cryo-electron microscopic and X-ray crystallographic analysis of the light-driven proton pump proteorhodopsin reveals a pentameric assembly. JOURNAL OF STRUCTURAL BIOLOGY-X 2020; 4:100024. [PMID: 32647827 PMCID: PMC7337067 DOI: 10.1016/j.yjsbx.2020.100024] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Revised: 03/05/2020] [Accepted: 03/06/2020] [Indexed: 11/30/2022]
Abstract
Affinity tag-free isolation of proteorhodopsin (PR) by ion exchange and size exclusion chromatography. Biochemical and computational analysis indicate a single, pentameric PR population. Highly pure and homogeneous PR enables growth of 3D crystals. X-ray crystallography and cryo-electron microscopy reveal pentameric assembly of PR.
The green-light absorbing proteorhodopsin (GPR) is the prototype of bacterial light-driven proton pumps. It has been the focus of continuous research since its discovery 20 years ago and has sparked the development and application of various biophysical techniques. However, a certain controversy and ambiguity about the oligomeric assembly of GPR still remains. We present here the first tag-free purification of pentameric GPR. The combination of ion exchange and size exclusion chromatography yields homogeneous and highly pure untagged pentamers from GPR overexpressing Escherichia coli. The presented purification procedure provides native-like protein and excludes the need for affinity purification tags. Importantly, three-dimensional protein crystals of GPR were successfully grown and analyzed by X-ray crystallography. These results together with data from single particle cryo-electron microscopy provide direct evidence for the pentameric stoichiometry of purified GPR.
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Affiliation(s)
- Stephan Hirschi
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bühlstrasse 28, 3012 Bern, Switzerland
| | - David Kalbermatter
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bühlstrasse 28, 3012 Bern, Switzerland
| | - Zöhre Ucurum
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bühlstrasse 28, 3012 Bern, Switzerland
| | - Dimitrios Fotiadis
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bühlstrasse 28, 3012 Bern, Switzerland
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Laloux T, Junqueira B, Maistriaux LC, Ahmed J, Jurkiewicz A, Chaumont F. Plant and Mammal Aquaporins: Same but Different. Int J Mol Sci 2018; 19:E521. [PMID: 29419811 PMCID: PMC5855743 DOI: 10.3390/ijms19020521] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 01/31/2018] [Accepted: 02/01/2018] [Indexed: 02/06/2023] Open
Abstract
Aquaporins (AQPs) constitute an ancient and diverse protein family present in all living organisms, indicating a common ancient ancestor. However, during evolution, these organisms appear and evolve differently, leading to different cell organizations and physiological processes. Amongst the eukaryotes, an important distinction between plants and animals is evident, the most conspicuous difference being that plants are sessile organisms facing ever-changing environmental conditions. In addition, plants are mostly autotrophic, being able to synthesize carbohydrates molecules from the carbon dioxide in the air during the process of photosynthesis, using sunlight as an energy source. It is therefore interesting to analyze how, in these different contexts specific to both kingdoms of life, AQP function and regulation evolved. This review aims at highlighting similarities and differences between plant and mammal AQPs. Emphasis is given to the comparison of isoform numbers, their substrate selectivity, the regulation of the subcellular localization, and the channel activity.
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Affiliation(s)
- Timothée Laloux
- Institut des Sciences de la Vie, Université catholique de Louvain, Croix du Sud 4-L7.07.14, B-1348 Louvain-la Neuve, Belgium.
| | - Bruna Junqueira
- Institut des Sciences de la Vie, Université catholique de Louvain, Croix du Sud 4-L7.07.14, B-1348 Louvain-la Neuve, Belgium.
| | - Laurie C Maistriaux
- Institut des Sciences de la Vie, Université catholique de Louvain, Croix du Sud 4-L7.07.14, B-1348 Louvain-la Neuve, Belgium.
| | - Jahed Ahmed
- Institut des Sciences de la Vie, Université catholique de Louvain, Croix du Sud 4-L7.07.14, B-1348 Louvain-la Neuve, Belgium.
| | - Agnieszka Jurkiewicz
- Institut des Sciences de la Vie, Université catholique de Louvain, Croix du Sud 4-L7.07.14, B-1348 Louvain-la Neuve, Belgium.
| | - François Chaumont
- Institut des Sciences de la Vie, Université catholique de Louvain, Croix du Sud 4-L7.07.14, B-1348 Louvain-la Neuve, Belgium.
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Sutka M, Amodeo G, Ozu M. Plant and animal aquaporins crosstalk: what can be revealed from distinct perspectives. Biophys Rev 2017; 9:545-562. [PMID: 28871493 DOI: 10.1007/s12551-017-0313-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Accepted: 08/02/2017] [Indexed: 01/03/2023] Open
Abstract
Aquaporins (AQPs) can be revisited from a distinct and complementary perspective: the outcome from analyzing them from both plant and animal studies. (1) The approach in the study. Diversity found in both kingdoms contrasts with the limited number of crystal structures determined within each group. While the structure of almost half of mammal AQPs was resolved, only a few were resolved in plants. Strikingly, the animal structures resolved are mainly derived from the AQP2-lineage, due to their important roles in water homeostasis regulation in humans. The difference could be attributed to the approach: relevance in animal research is emphasized on pathology and in consequence drug screening that can lead to potential inhibitors, enhancers and/or regulators. By contrast, studies on plants have been mainly focused on the physiological role that AQPs play in growth, development and stress tolerance. (2) The transport capacity. Besides the well-described AQPs with high water transport capacity, large amount of evidence confirms that certain plant AQPs can carry a large list of small solutes. So far, animal AQP list is more restricted. In both kingdoms, there is a great amount of evidence on gas transport, although there is still an unsolved controversy around gas translocation as well as the role of the central pore of the tetramer. (3) More roles than expected. We found it remarkable that the view of AQPs as specific channels has evolved first toward simple transporters to molecules that can experience conformational changes triggered by biochemical and/or mechanical signals, turning them also into signaling components and/or behave as osmosensor molecules.
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Affiliation(s)
- Moira Sutka
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires e Instituto de Biodiversidad y Biología Experimental, Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Gabriela Amodeo
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires e Instituto de Biodiversidad y Biología Experimental, Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina.
| | - Marcelo Ozu
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires e Instituto de Biodiversidad y Biología Experimental, Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina.
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11
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Fowler PW, Hélie J, Duncan A, Chavent M, Koldsø H, Sansom MSP. Membrane stiffness is modified by integral membrane proteins. SOFT MATTER 2016; 12:7792-7803. [PMID: 27722554 PMCID: PMC5314686 DOI: 10.1039/c6sm01186a] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Accepted: 08/25/2016] [Indexed: 05/12/2023]
Abstract
The ease with which a cell membrane can bend and deform is important for a wide range of biological functions. Peripheral proteins that induce curvature in membranes (e.g. BAR domains) have been studied for a number of years. Little is known, however, about the effect of integral membrane proteins on the stiffness of a membrane (characterised by the bending rigidity, Kc). We demonstrate by computer simulation that adding integral membrane proteins at physiological densities alters the stiffness of the membrane. First we establish that the coarse-grained MARTINI forcefield is able to accurately reproduce the bending rigidity of a small patch of 1500 phosphatidyl choline lipids by comparing the calculated value to both experiment and an atomistic simulation of the same system. This enables us to simulate the dynamics of large (ca. 50 000 lipids) patches of membrane using the MARTINI coarse-grained description. We find that altering the lipid composition changes the bending rigidity. Adding integral membrane proteins to lipid bilayers also changes the bending rigidity, whilst adding a simple peripheral membrane protein has no effect. Our results suggest that integral membrane proteins can have different effects, and in the case of the bacterial outer membrane protein, BtuB, the greater the density of protein, the larger the reduction in stiffness.
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Affiliation(s)
- Philip W Fowler
- Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK.
| | - Jean Hélie
- Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK.
| | - Anna Duncan
- Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK.
| | - Matthieu Chavent
- Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK.
| | - Heidi Koldsø
- Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK.
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK.
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12
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Chauvigné F, Fjelldal PG, Cerdà J, Finn RN. Auto-Adhesion Potential of Extraocular Aqp0 during Teleost Development. PLoS One 2016; 11:e0154592. [PMID: 27153052 PMCID: PMC4859563 DOI: 10.1371/journal.pone.0154592] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 04/17/2016] [Indexed: 11/25/2022] Open
Abstract
AQP0 water channels are the most abundant proteins expressed in the mammalian lens fiber membranes where they are essential for lens development and transparency. Unlike other aquaporin paralogs, mammalian AQP0 has a low intrinsic water permeability, but can form cell-to-cell junctions between the lens fibers. It is not known whether the adhesive properties of AQP0 is a derived feature found only in mammals, or exists as a conserved ancestral trait in non-mammalian vertebrates. Here we show that a tetraploid teleost, the Atlantic salmon, expresses four Aqp0 paralogs in the developing lens, but also expresses significant levels of aqp0 mRNAs and proteins in the epithelia of the pronephros, presumptive enterocytes, gill filament and epidermis. Quantitative PCR reveals that aqp0 mRNA titres increase by three orders of magnitude between the onset of somitogenesis and pigmentation of the eye. Using in situ hybridization and specific antisera, we show that at least two of the channels (Aqp0a1, -0b1 and/or -0b2) are localized in the extraocular basolateral and apical membranes, while Aqp0a2 is lens-specific. Heterologous expression of the Aqp0 paralogs in adhesion-deficient mouse fibolast L-cells reveals that, as for human AQP0, each intact salmon channel retains cell-to-cell adhesive properties. The strongest Aqp0 interactions are auto-adhesion, suggesting that homo-octamers likely form the intercellular junctions of the developing lens and epithelial tissues. The present data are thus the first to show the adhesion potential of Aqp0 channels in a non-mammalian vertebrate, and further uncover a novel extraocular role of the channels during vertebrate development.
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Affiliation(s)
- François Chauvigné
- Department of Biology, Bergen High Technology Centre, University of Bergen, 5020 Bergen, Norway
- Institute of Marine Research, Nordnes, 5817 Bergen, Norway
- * E-mail: (RNF); (FC)
| | | | - Joan Cerdà
- Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), 08003 Barcelona, Spain
| | - Roderick Nigel Finn
- Department of Biology, Bergen High Technology Centre, University of Bergen, 5020 Bergen, Norway
- Institute of Marine Research, Nordnes, 5817 Bergen, Norway
- * E-mail: (RNF); (FC)
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Petrova RS, Schey KL, Donaldson PJ, Grey AC. Spatial distributions of AQP5 and AQP0 in embryonic and postnatal mouse lens development. Exp Eye Res 2015; 132:124-35. [PMID: 25595964 DOI: 10.1016/j.exer.2015.01.011] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 12/19/2014] [Accepted: 01/12/2015] [Indexed: 12/11/2022]
Abstract
The expression of the water channel protein aquaporin (AQP)-5 in adult rodent and human lenses was recently reported using immunohistochemistry, molecular biology, and mass spectrometry techniques, confirming a second transmembrane water channel that is present in lens fibre cells in addition to the abundant AQP0 protein. Interestingly, the sub-cellular distribution and level of post-translational modification of both proteins changes with fibre cell differentiation and location in the adult rodent lens. This study compares the sub-cellular distribution of AQP0 and AQP5 during embryonic and postnatal fibre cell development in the mouse lens to understand how the immunolabelling patterns for both AQPs observed in adult lens are first established. Immunohistochemistry was used to map the cellular and sub-cellular distribution of AQP5 and AQP0 throughout the lens in cryosections from adult (6 weeks-8 months) and postnatal (0-2 weeks) mouse lenses and in sections from paraffin embedded mouse embryos (E10-E19). All sections were imaged by fluorescence confocal microscopy. Using antibodies directed against the C-terminus of each AQP, AQP5 was abundantly expressed early in development, being found in the cytoplasm of cells of the lens vesicle and surrounding tissues (E10), while AQP0 was detected later (E11), and only in the membranes of elongating primary fibre cells. During the course of subsequent embryonic and postnatal development the pattern of cytoplasmic AQP5 and membranous AQP0 labelling was maintained until postnatal day 6 (P6). From P6 AQP5 labelling became progressively more membranous initially in the lens nucleus and then later in all regions of the lens, while AQP0 labelling was abruptly lost in the lens nucleus due to C-terminal truncation. Our results show that the spatial distribution patterns of AQP0 and AQP5 observed in the adult lens are established during a narrow window of postnatal development (P6-P15) that precedes eye opening and coincides with regression of the hyaloid vascular system. Our results support the hypothesis that, in the older fibre cells, insertion of AQP5 into the fibre cell membrane may compensate for any change in the functionality of AQP0 induced by truncation of its C-terminal tail.
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Affiliation(s)
- Rosica S Petrova
- School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Kevin L Schey
- Departments of Biochemistry and Ophthalmology, Vanderbilt University, Nashville, TN, USA
| | - Paul J Donaldson
- School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Angus C Grey
- School of Medical Sciences, University of Auckland, Auckland, New Zealand.
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14
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Baturin S, Galka JJ, Piyadasa H, Gajjeraman S, O'Neil JD. The effects of a protein osmolyte on the stability of the integral membrane protein glycerol facilitator. Biochem Cell Biol 2014; 92:564-75. [PMID: 25387032 DOI: 10.1139/bcb-2014-0076] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Osmolytes are naturally occurring molecules used by a wide variety of organisms to stabilize proteins under extreme conditions of temperature, salinity, hydrostatic pressure, denaturant concentration, and desiccation. The effects of the osmolyte trimethylamine N-oxide (TMAO) as well as the influence of detergent head group and acyl chain length on the stability of the Escherichia coli integral membrane protein glycerol facilitator (GF) tetramer to thermal and chemical denaturation by sodium dodecyl sulphate (SDS) are reported. TMAO promotes the association of the normally tetrameric α-helical protein into higher order oligomers in dodecyl-maltoside (DDM), but not in tetradecyl-maltoside (TDM), lyso-lauroylphosphatidyl choline (LLPC), or lyso-myristoylphosphatidyl choline (LMPC), as determined by dynamic light scattering (DLS); an octameric complex is particularly stable as indicated by SDS polyacrylamide gel electrophoresis. TMAO increases the heat stability of the GF tetramer an average of 10 °C in the 4 detergents and also protects the protein from denaturation by SDS. However, it did not promote re-association to the tetramer when added to SDS-dissociated protein. TMAO also promotes the formation of rod-like detergent micelles, and DLS was found to be useful for monitoring the structure of the protein and the redistribution of detergent during thermal dissociation of the protein. The protein is more thermally stable in detergents with the phosphatidylcholine head group (LLPC and LMPC) than in the maltoside detergents. The implications of the results for osmolyte mechanism, membrane protein stability, and protein-protein interactions are discussed.
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Affiliation(s)
- Simon Baturin
- Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
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15
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Grey AC, Walker KL, Petrova RS, Han J, Wilmarth PA, David LL, Donaldson PJ, Schey KL. Verification and spatial localization of aquaporin-5 in the ocular lens. Exp Eye Res 2013; 108:94-102. [PMID: 23313152 DOI: 10.1016/j.exer.2012.12.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2012] [Revised: 12/07/2012] [Accepted: 12/10/2012] [Indexed: 12/25/2022]
Abstract
Until recently, the lens was thought to express only two aquaporin (AQP) water channels, AQP1 and AQP0. In this study we confirm lenticular AQP5 protein expression by Western blotting and mass spectrometry in lenses from a variety of species. In addition, confocal microscopy was used to map cellular distributions of AQP5 in mouse, rat and human lenses. Tandem mass spectrometry of a human lens membrane preparation revealed extensive sequence coverage (56.2%) of AQP5. Western blotting performed on total fiber cell membranes from mouse, rat, bovine and human lenses confirmed AQP5 protein expression is conserved amongst species. Western blotting of dissected lens fractions suggests that AQP5 is processed in the lens core by C-terminal truncation. Immunohistochemistry showed that AQP5 signal was most abundant in the lens outer cortex and decreased in intensity in the lens core. Furthermore, AQP5 undergoes differentiation-dependent changes in subcellular location from an intracellular localization in differentiating fiber cells to the plasma membrane of mature fiber cells upon the loss of fiber cell nuclei. Our results show that AQP5 is a significant component of lens fiber cell membranes, representing the second most abundant water channel in these cells. Together, the changes to AQP5 distribution and structure are likely to modulate the functional role of AQP5 in different regions of the lens.
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Affiliation(s)
- Angus C Grey
- Department of Optometry and Vision Science, New Zealand National Eye Centre, University of Auckland, Auckland, New Zealand
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16
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Structural features of aquaporin 4 supporting the formation of arrays and junctions in biomembranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:2234-43. [PMID: 22554469 DOI: 10.1016/j.bbamem.2012.04.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Revised: 04/11/2012] [Accepted: 04/12/2012] [Indexed: 01/08/2023]
Abstract
A limited class of aquaporins has been described to form regular arrays and junctions in membranes. The biological significance of these structures, however, remains uncertain. Here we analyze the underlying physical principles with the help of a computational procedure that takes into account protein-protein as well as protein-membrane interactions. Experimentally observed array/junction structures are systematically (dis)assembled and major driving forces identified. Aquaporin 4 was found to be markedly different from the non-junction forming aquaporin 1. The environmental stabilization resulting from embedding into the biomembrane was identified as the main driving force. This highlights the role of protein-membrane interactions in aquaporin 4. Analysis of the type presented here can help to decipher the biological role of membrane arrays and junctions formed by aquaporin.
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17
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Unique and analogous functions of aquaporin 0 for fiber cell architecture and ocular lens transparency. Biochim Biophys Acta Mol Basis Dis 2011; 1812:1089-97. [PMID: 21511033 DOI: 10.1016/j.bbadis.2011.04.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Revised: 03/24/2011] [Accepted: 04/01/2011] [Indexed: 11/20/2022]
Abstract
Aquaporin (AQP) 1 and AQP0 water channels are expressed in lens epithelial and fiber cells, respectively, facilitating fluid circulation for nourishing the avascular lens to maintain transparency. Even though AQP0 water permeability is 40-fold less than AQP1, AQP0 is selectively expressed in the fibers. Delimited AQP0 fiber expression is attributed to a unique structural role as an adhesion protein. To validate this notion, we determined if wild type (WT) lens ultrastructure and fiber cell adhesion are different in AQP0(-/-), and TgAQP1(+/+)/AQP0(-/-) mice that transgenically express AQP1 (TgAQP1) in fiber cells without AQP0 (AQP0(-/-)). In WT, lenses were transparent with 'Y' sutures. Fibers contained opposite end curvature, lateral interdigitations, hexagonal shape, and were arranged as concentric growth shells. AQP0(-/-) lenses were cataractous, lacked 'Y' sutures, ordered packing and well-defined lateral interdigitations. TgAQP1(+/+)/AQP0(-/-) lenses showed improvement in transparency and lateral interdigitations in the outer cortex while inner cortex and nuclear fibers were severely disintegrated. Transmission electron micrographs exhibited tightly packed fiber cells in WT whereas AQP0(-/-) and TgAQP1(+/+)/AQP0(-/-) lenses had wide extracellular spaces. Fibers were easily separable by teasing in AQP0(-/-) and TgAQP1(+/+)/AQP0(-/-) lenses compared to WT. Our data suggest that the increased water permeability through AQP1 does not compensate for loss of AQP0 expression in TgAQP1(+/+)/AQP0(-/-) mice. Fiber cell AQP0 expression is required to maintain their organization, which is a requisite for lens transparency. AQP0 appears necessary for cell-to-cell adhesion and thereby to minimize light scattering since in the AQP0(-/-) and TgAQP1(+/+)/AQP0(-/-) lenses, fiber cell disorganization was evident.
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18
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Nielsen CH. Major intrinsic proteins in biomimetic membranes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 679:127-42. [PMID: 20666229 DOI: 10.1007/978-1-4419-6315-4_10] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Biological membranes define the structural and functional boundaries in living cells and their organelles. The integrity of the cell depends on its ability to separate inside from outside and yet at the same time allow massive transport of matter in and out the cell. Nature has elegantly met this challenge by developing membranes in the form of lipid bilayers in which specialized transport proteins are incorporated. This raises the question: is it possible to mimic biological membranes and create a membrane based sensor and/or separation device? In the development of a biomimetic sensor/separation technology, a unique class of membrane transport proteins is especially interesting-the major intrinsic proteins (MIPs). Generally, MIPs conduct water molecules and selected solutes in and out of the cell while preventing the passage of other solutes, a property critical for the conservation of the cells internal pH and salt concentration. Also known as water channels or aquaporins they are highly efficient membrane pore proteins some of which are capable of transporting water at very high rates up to 10(9) molecules per second. Some MIPs transport other small, uncharged solutes, such as glycerol and other permeants such as carbon dioxide, nitric oxide, ammonia, hydrogen peroxide and the metalloids antimonite, arsenite, silicic and boric acid depending on the effective restriction mechanism of the protein. The flux properties of MIPs thus lead to the question ifMIPs can be used in separation devices or as sensor devices based on, e.g., the selective permeation of metalloids. In principle a MIP based membrane sensor/separation device requires the supporting biomimetic matrix to be virtually impermeable to anything but water or the solute in question. In practice, however, a biomimetic support matrix will generally have finite permeabilities to both electrolytes and non-electrolytes. The feasibility of a biomimetic MIP device thus depends on the relative transport contribution from both protein and biomimetic support matrix. Also the biomimetic matrix must be encapsulated in order to protect it and make it sufficiently stable in a final application. Here, I specifically discuss the feasibility of developing osmotic biomimetic MIP membranes, but the technical issues are of general concern in the design ofbiomimetic membranes capable of supporting selective transmembrane fluxes.
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Affiliation(s)
- Claus Hélix Nielsen
- Quantrum Protein Center, Department of Physics, Technical University of Denmark, DK-2800 Lyngby.
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19
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Abstract
Membrane proteins (MPs) are responsible for the interface between the exterior and the interior of the cell. These proteins are involved in numerous diseases, like cancer, cystic fibrosis, epilepsy, hyperinsulinism, heart failure, hypertension and Alzheimer disease. However, studies of these disorders are hampered by a lack of structural information about the proteins involved. Structural analysis requires large quantities of pure and active proteins. The majority of medically and pharmaceutically relevant MPs are present in tissues at low concentration, which makes heterologous expression in large-scale production-adapted cells a prerequisite for structural studies. Obtaining mammalian MP structural data depends on the development of methods that allow the production of large quantities of MPs. This review focuses on the heterologous expression systems now available to produce large amounts of MPs for structural proteomics, and describes the strategies that allowed the determination of the structure of the first heterologously expressed mammalian MPs.
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Affiliation(s)
- Isabelle Mus-Veteau
- Institut of Developmental Biology and Cancer, UMR CNRS, Université de Nice-Sophia Antipolis, Nice, France.
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20
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Koth CMM, Payandeh J. Strategies for the cloning and expression of membrane proteins. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2009; 76:43-86. [PMID: 20663478 DOI: 10.1016/s1876-1623(08)76002-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Abstract
Despite the determination of thousands of high-resolution structures of soluble proteins, many features of integral membrane proteins render them difficult targets for the structural biologist. Among these, the most important challenge is in expressing sufficient quantities of active protein to support downstream purification and structure determination efforts. Over 190 unique membrane protein structures have now been solved, and noticeable trends in successful expression strategies are beginning to emerge. A number of groups have also explored high-throughput (HTP) methods for membrane protein expression, with varying degrees of success. Here we review the current state of expressing membrane proteins for functional and structural studies. We first survey successful methods that have already yielded levels of membrane protein expression sufficient for structure determination. HTP methods are also examined since these aim to explore large numbers of targets and can predict reasonable starting points for many membrane proteins. Since HTP techniques may fail, particularly for certain classes of eukaryotic targets, detailed strategies for the expression of two prominent classes of eukaryotic protein families, G-protein-coupled receptors and ion channels, are also summarized.
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Affiliation(s)
- Christopher M M Koth
- Department of Structural Biology, Genentech, South San Francisco, California 94080, USA
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21
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Kumari SS, Varadaraj K. Intact AQP0 performs cell-to-cell adhesion. Biochem Biophys Res Commun 2009; 390:1034-9. [PMID: 19857466 DOI: 10.1016/j.bbrc.2009.10.103] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Accepted: 10/21/2009] [Indexed: 10/20/2022]
Abstract
Aquaporins (AQPs) constitute a major conduit for movement of water across plasma membranes. AQP0 is expressed in the fiber cells and is critical for lens transparency and homeostasis as mutations and knockout have resulted in dominant lens cataract. Several functions have been attributed for AQP0. In vitro and ex vivo experiments from several laboratories have confirmed the water permeability function of AQP0. However, this function seems paradoxical when the lens switches protein expression from AQP1 in the equatorial epithelial cells to 40 times less efficient AQP0 in the differentiating fiber cells. A possible explanation is AQP0 may perform unique function/s besides being a water pore. Indirect evidences including those from structural studies indicate a cell-to-cell adhesion role for AQP0. However, there is a lack of experimental evidence directly demonstrating the cell-to-cell adhesion capability of AQP0. We studied the adhesion property of human intact AQP0 by expressing it in adhesion-deficient mouse fibroblast L-cells using a newly devised method as well as a traditional assay. Our results reveal that AQP0 indeed can perform cell-to-cell adhesion. AQP1, two alternate splice variants of AQP4 (AQP4-M1and AQP4-M23) and E-cadherin were also tested to validate the results. Cell-to-cell adhesion and cell aggregation properties of AQP0 expressing L-cells were less than those of the positive control L-cells expressing mouse E-cadherin and greater than those of AQP4-M23. AQP1 or AQP4-M1 expressing cells did not show cell-to-cell adhesion or cell aggregation. To our knowledge, this is the first report validating the possible structural role of intact AQP0 as a cell-to-cell adhesion protein, using an in vitro expression system.
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Affiliation(s)
- S Sindhu Kumari
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
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22
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Chepelinsky AB. Structural function of MIP/aquaporin 0 in the eye lens; genetic defects lead to congenital inherited cataracts. Handb Exp Pharmacol 2008:265-97. [PMID: 19096783 DOI: 10.1007/978-3-540-79885-9_14] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Aquaporin 0 (AQP0) was originally characterized as a membrane intrinsic protein, specifically expressed in the lens fibers of the ocular lens and designated MIP, for major intrinsic protein of the lens. Once the gene was cloned, an internal repeat was identified, encoding for the amino acids Asp-Pro-Ala, the NPA repeat. Shortly, the MIP gene family was emerging, with members being characterized in mammals, insects, and plants. Once Peter Agre's laboratory developed a functional assay for water channels, the MIP family became the aquaporin family and MIP became known as aquaporin 0. Besides functioning as a water channel, aquaporin 0 also plays a structural role, being required for maintaining the transparency and optical accommodation of the ocular lens. Mutations in the AQP0 gene in human and mice result in genetic cataracts; deletion of the MIP/AQP0 gene in mice results in lack of suture formation required for maintenance of the lens fiber architecture, resulting in perturbed accommodation and focus properties of the ocular lens. Crystallography studies support the notion of the double function of aquaporin 0 as a water channel (open configuration) or adhesion molecule (closed configuration) in the ocular lens fibers. The functions of MIP/AQP0, both as a water channel and an adhesive molecule in the lens fibers, contribute to the narrow intercellular space of the lens fibers that is required for lens transparency and accommodation.
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Affiliation(s)
- Ana B Chepelinsky
- National Institutes of Health, National Eye Institute, Bldg. 31, Room 6A-32, Bethesda, MD, 20892-2510, USA.
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23
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Differentiation-dependent modification and subcellular distribution of aquaporin-0 suggests multiple functional roles in the rat lens. Differentiation 2008; 77:70-83. [PMID: 19281766 DOI: 10.1016/j.diff.2008.09.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2008] [Revised: 08/05/2008] [Accepted: 08/05/2008] [Indexed: 11/21/2022]
Abstract
Using immunohistochemistry and mass spectrometry, differentiation-dependent changes in the subcellular distribution and processing of aquaporin-0 (AQP0) have been mapped in the rat lens. Sections labelled with C-terminal tail AQP0 antibodies yielded two concentric rings of labelling with minimal signal in the lens core. The rings were separated by a transient zone of decreased labelling located prior to the transition of differentiating fiber (DF) cells into mature denucleated fiber (MF) cells. Mass spectrometry showed that the loss of core labelling was due to AQP0 cleavage, while the transient loss of labelling was more likely caused by masking of the antibody epitope. AQP0 subcellular distribution changed with radial distance into the lens. In peripheral DF cells, AQP0 was found throughout both broad and narrow side membranes. In deeper-lying DF cells, AQP0 aggregated into plaque-like structures located on the broad sides. This shift occurred prior to the transient loss of AQP0 signal, and coincided with formation of broad-side membrane invaginations between adjacent fiber cells to which filensin, a known binding partner of AQP0, was also localized. After nuclei loss, AQP0 was once again distributed throughout MF cell membranes. In the absence of protein synthesis, the observed subcellular redistribution of AQP0 in DF and subsequent cleavage of AQP0 in MF are suggestive of a switch in the function of AQP0 from a water channel to a junctional protein.
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24
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Dynamic control of slow water transport by aquaporin 0: implications for hydration and junction stability in the eye lens. Proc Natl Acad Sci U S A 2008; 105:14430-5. [PMID: 18787121 DOI: 10.1073/pnas.0802401105] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Aquaporin 0 (AQP0), the most abundant membrane protein in mammalian lens fiber cells, not only serves as the primary water channel in this tissue but also appears to mediate the formation of thin junctions between fiber cells. AQP0 is remarkably less water permeable than other aquaporins, but the structural basis and biological significance of this low permeability remain uncertain, as does the permeability of the protein in a reported junctional form. To address these issues, we performed molecular dynamics (MD) simulations of water transport through membrane-embedded AQP0 in both its (octameric) junctional and (tetrameric) nonjunctional forms. From our simulations, we measured an osmotic permeability for the nonjunctional form that agrees with experiment and found that the distinct dynamics of the conserved, lumen-protruding side chains of Tyr-23 and Tyr-149 modulate water passage, accounting for the slow permeation. The junctional and nonjunctional forms conducted water equivalently, in contrast to a previous suggestion based on static crystal structures that water conduction is lost on junction formation. Our analysis suggests that the low water permeability of AQP0 may help maintain the mechanical stability of the junction. We hypothesize that the structural features leading to low permeability may have evolved in part to allow AQP0 to form junctions that both conduct water and contribute to the organizational structure of the fiber cell tissue and microcirculation within it, as required to maintain transparency of the lens.
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25
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Sorani MD, Manley GT, Giacomini KM. Genetic variation in human aquaporins and effects on phenotypes of water homeostasis. Hum Mutat 2008; 29:1108-17. [DOI: 10.1002/humu.20762] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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26
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Galka JJ, Baturin SJ, Manley DM, Kehler AJ, O’Neil JD. Stability of the Glycerol Facilitator in Detergent Solutions. Biochemistry 2008; 47:3513-24. [DOI: 10.1021/bi7021409] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Jamie J. Galka
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada
| | - Simon J. Baturin
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada
| | - Darren M. Manley
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada
| | - Angela J. Kehler
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada
| | - Joe D. O’Neil
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canada
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27
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Engel A, Fujiyoshi Y, Gonen T, Walz T. Junction-forming aquaporins. Curr Opin Struct Biol 2008; 18:229-35. [PMID: 18194855 DOI: 10.1016/j.sbi.2007.11.003] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2007] [Revised: 11/06/2007] [Accepted: 11/07/2007] [Indexed: 01/26/2023]
Abstract
Aquaporins (AQPs) are a family of ubiquitous membrane channels that conduct water and solutes across membranes. This review focuses on AQP0 and AQP4, which in addition to forming water channels also appear to play a role in cell adhesion. We discuss the recently determined structures of the membrane junctions mediated by these two AQPs, the mechanisms that regulate junction formation, and evidence that supports a role for AQP0 and AQP4 in cell adhesion.
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Affiliation(s)
- Andreas Engel
- Maurice E. Mueller Institute, University of Basel, Biozentrum, Klingelberstrasse 70, CH-4056 Basel, Switzerland
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28
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Midgett CR, Madden DR. Breaking the bottleneck: Eukaryotic membrane protein expression for high-resolution structural studies. J Struct Biol 2007; 160:265-74. [PMID: 17702603 DOI: 10.1016/j.jsb.2007.07.001] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Revised: 06/26/2007] [Accepted: 07/06/2007] [Indexed: 10/23/2022]
Abstract
The recombinant expression of eukaryotic membrane proteins has been a major stumbling block in efforts to determine their structures. In the last two years, however, five such proteins have yielded high-resolution X-ray or electron diffraction data, opening the prospect of increased throughput for eukaryotic membrane protein structure determination. Here, we summarize the major expression systems available, and highlight technical advances that should facilitate more systematic screening of expression conditions for this physiologically important class of targets.
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Affiliation(s)
- Charles R Midgett
- Department of Biochemistry, Dartmouth Medical School, 7200 Vail Building, Hanover, NH 03755, USA
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29
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Hite RK, Raunser S, Walz T. Revival of electron crystallography. Curr Opin Struct Biol 2007; 17:389-95. [PMID: 17723294 PMCID: PMC2040057 DOI: 10.1016/j.sbi.2007.06.006] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2007] [Accepted: 06/13/2007] [Indexed: 11/21/2022]
Abstract
Since the structure determination of bacteriorhodopsin in 1990, much progress has been made in the further development and use of electron crystallography. In this review, we provide a concise overview of the new developments in electron crystallography concerning 2D crystallization, data collection and data processing. Based on electron crystallographic work on bacteriorhodopsin, the acetylcholine receptor and aquaporins, we highlight the unique advantages and future perspectives of electron crystallography for the structural study of membrane proteins. These advantages include the visualization of membrane proteins in their native environment without detergent-induced artifacts, the trapping of different states in a reaction pathway by time-resolved experiments, the study of non-specific protein-lipid interactions and the characterization of the charge state of individual residues in membrane proteins.
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Affiliation(s)
- Richard K Hite
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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30
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Hedfalk K, Törnroth-Horsefield S, Nyblom M, Johanson U, Kjellbom P, Neutze R. Aquaporin gating. Curr Opin Struct Biol 2006; 16:447-56. [PMID: 16837191 DOI: 10.1016/j.sbi.2006.06.009] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2006] [Revised: 06/02/2006] [Accepted: 06/27/2006] [Indexed: 10/24/2022]
Abstract
An acceleration in the rate at which new aquaporin structures are determined means that structural models are now available for mammalian AQP0, AQP1, AQP2 and AQP4, bacterial GlpF, AqpM and AQPZ, and the plant SoPIP2;1. With an apparent consensus emerging concerning the mechanism of selective water transport and proton extrusion, emphasis has shifted towards the issues of substrate selectivity and the mechanisms of aquaporin regulation. In particular, recently determined structures of plant SoPIP2;1, sheep and bovine AQP0, and Escherichia coli AQPZ provide new insights into the underlying structural mechanisms by which water transport rates are regulated in diverse organisms. From these results, two distinct pictures of 'capping' and 'pinching' have emerged to describe aquaporin gating.
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Affiliation(s)
- Kristina Hedfalk
- Chalmers University of Technology, Department of Chemistry and Bioscience, SE-405 30 Göteborg, Sweden
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Dunia I, Cibert C, Gong X, Xia CH, Recouvreur M, Levy E, Kumar N, Bloemendal H, Benedetti EL. Structural and immunocytochemical alterations in eye lens fiber cells from Cx46 and Cx50 knockout mice. Eur J Cell Biol 2006; 85:729-52. [PMID: 16740340 DOI: 10.1016/j.ejcb.2006.03.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2005] [Revised: 03/02/2006] [Accepted: 03/07/2006] [Indexed: 11/28/2022] Open
Abstract
In the current study we describe the changes of overall organization of lens fiber cells in connexin 46 (Cx46) and connexin 50 (Cx50) knockout mice. Morphometric analyses and the application of immunocytochemical techniques revealed that in Cx46 knockout lens (Cx46 -/-), where Cx50 is expressed alone, the postnatal differentiation of secondary fiber cells proceeds faster and is characterized by an increased number of smaller fiber cells. Conversely, in Cx50 knockout mice (Cx50 -/-), the lenticular mass is considerably reduced and characterized by a small number of fiber cells added during the postnatal period. The process of terminal differentiation was impaired and generated larger fiber cells still possessing cytoplasmic organelles. Freeze-fracture and fracture labeling revealed that the junctional assembly, packing organization and topographic interactions between connexons and MP26 differed when Cx46 and Cx50 were co-assembled in the wild-type or expressed separately in the two distinct knockout phenotypes. Filipin cytochemistry provided indirect evidence that Cx46 and Cx50 expressed alone are recruited into different lipid environments. Our results represent the structural proof that interaction of connexins and MP26 contributes to the overall organization of the fiber cells.
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Affiliation(s)
- Irene Dunia
- Biologie Cellulaire, Institut Jacques Monod, CNRS, Universités Paris 6-Paris 7, 2, place Jussieu, F-75251 Paris Cedex 5, France.
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