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Chiu PL, Orjuela JD, de Groot BL, Aponte Santamaría C, Walz T. Structure and dynamics of cholesterol-mediated aquaporin-0 arrays and implications for lipid rafts. eLife 2024; 12:RP90851. [PMID: 39222068 PMCID: PMC11368405 DOI: 10.7554/elife.90851] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/04/2024] Open
Abstract
Aquaporin-0 (AQP0) tetramers form square arrays in lens membranes through a yet unknown mechanism, but lens membranes are enriched in sphingomyelin and cholesterol. Here, we determined electron crystallographic structures of AQP0 in sphingomyelin/cholesterol membranes and performed molecular dynamics (MD) simulations to establish that the observed cholesterol positions represent those seen around an isolated AQP0 tetramer and that the AQP0 tetramer largely defines the location and orientation of most of its associated cholesterol molecules. At a high concentration, cholesterol increases the hydrophobic thickness of the annular lipid shell around AQP0 tetramers, which may thus cluster to mitigate the resulting hydrophobic mismatch. Moreover, neighboring AQP0 tetramers sandwich a cholesterol deep in the center of the membrane. MD simulations show that the association of two AQP0 tetramers is necessary to maintain the deep cholesterol in its position and that the deep cholesterol increases the force required to laterally detach two AQP0 tetramers, not only due to protein-protein contacts but also due to increased lipid-protein complementarity. Since each tetramer interacts with four such 'glue' cholesterols, avidity effects may stabilize larger arrays. The principles proposed to drive AQP0 array formation could also underlie protein clustering in lipid rafts.
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Affiliation(s)
- Po-Lin Chiu
- Department of Cell Biology, Harvard Medical SchoolBostonUnited States
| | - Juan D Orjuela
- Max Planck Tandem Group in Computational Biophysics, Universidad de los AndesBogotáColombia
- Biomedical Engineering Department, Universidad de los AndesBogotáColombia
| | - Bert L de Groot
- Computational Biomolecular Dynamics Group, Max Planck Institute for Multidisciplinary SciencesGöttingenGermany
| | - Camilo Aponte Santamaría
- Max Planck Tandem Group in Computational Biophysics, Universidad de los AndesBogotáColombia
- Molecular Biomechanics Group, Heidelberg Institute for Theoretical StudiesHeidelbergGermany
| | - Thomas Walz
- Department of Cell Biology, Harvard Medical SchoolBostonUnited States
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Chiu PL, Orjuela JD, de Groot BL, Aponte-Santamaría C, Walz T. Structure and dynamics of cholesterol-mediated aquaporin-0 arrays and implications for lipid rafts. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.05.16.540959. [PMID: 37292626 PMCID: PMC10245776 DOI: 10.1101/2023.05.16.540959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Aquaporin-0 (AQP0) tetramers form square arrays in lens membranes through a yet unknown mechanism, but lens membranes are enriched in sphingomyelin and cholesterol. Here, we determined electron crystallographic structures of AQP0 in sphingomyelin/cholesterol membranes and performed molecular dynamics (MD) simulations to establish that the observed cholesterol positions represent those seen around an isolated AQP0 tetramer and that the AQP0 tetramer largely defines the location and orientation of most of its associated cholesterol molecules. At a high concentration, cholesterol increases the hydrophobic thickness of the annular lipid shell around AQP0 tetramers, which may thus cluster to mitigate the resulting hydrophobic mismatch. Moreover, neighboring AQP0 tetramers sandwich a cholesterol deep in the center of the membrane. MD simulations show that the association of two AQP0 tetramers is necessary to maintain the deep cholesterol in its position and that the deep cholesterol increases the force required to laterally detach two AQP0 tetramers, not only due to protein-protein contacts but also due to increased lipid-protein complementarity. Since each tetramer interacts with four such 'glue' cholesterols, avidity effects may stabilize larger arrays. The principles proposed to drive AQP0 array formation could also underlie protein clustering in lipid rafts.
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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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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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Subczynski WK, Pasenkiewicz-Gierula M, Widomska J. Protecting the Eye Lens from Oxidative Stress through Oxygen Regulation. Antioxidants (Basel) 2023; 12:1783. [PMID: 37760086 PMCID: PMC10525422 DOI: 10.3390/antiox12091783] [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: 08/18/2023] [Revised: 09/08/2023] [Accepted: 09/18/2023] [Indexed: 09/29/2023] Open
Abstract
Molecular oxygen is a primary oxidant that is involved in the formation of active oxygen species and in the oxidation of lipids and proteins. Thus, controlling oxygen partial pressure (concentration) in the human organism, tissues, and organs can be the first step in protecting them against oxidative stress. However, it is not an easy task because oxygen is necessary for ATP synthesis by mitochondria and in many biochemical reactions taking place in all cells in the human body. Moreover, the blood circulatory system delivers oxygen to all parts of the body. The eye lens seems to be the only organ that is protected from the oxidative stress through the regulation of oxygen partial pressure. The basic mechanism that developed during evolution to protect the eye lens against oxidative damage is based on the maintenance of a very low concentration of oxygen within the lens. This antioxidant mechanism is supported by the resistance of both the lipid components of the lens membrane and cytosolic proteins to oxidation. Any disturbance, continuous or acute, in the working of this mechanism increases the oxygen concentration, in effect causing cataract development. Here, we describe the biophysical basis of the mechanism and its correlation with lens transparency.
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Affiliation(s)
| | - Marta Pasenkiewicz-Gierula
- Department of Computational Biophysics and Bioinformatics, Jagiellonian University, 30-387 Krakow, Poland;
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, 20-090 Lublin, Poland
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Mainali L, Raguz M, Subczynski WK. Quantification of Age-Related Changes in the Lateral Organization of the Lipid Portion of the Intact Membranes Isolated from the Left and Right Eye Lenses of the Same Human Donor. MEMBRANES 2023; 13:189. [PMID: 36837692 PMCID: PMC9958954 DOI: 10.3390/membranes13020189] [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: 12/11/2022] [Revised: 01/26/2023] [Accepted: 02/01/2023] [Indexed: 06/18/2023]
Abstract
The continuous wave EPR spin-labeling method was used to evaluate age-related changes in the amounts of phospholipids (PLs) and cholesterol (Chol) in domains present in intact, cortical, and nuclear fiber cell plasma membranes isolated separately from the left and right eye lenses of the same human donor. The relative amounts of boundary plus trapped PLs were evaluated with the PL analog 12-doxylstearic acid spin label (12-SASL) and the relative amounts of trapped Chol with the Chol analog androstane spin label (ASL). The donors ranged in age from 15 to 70 years. Both the left and right eye lenses from donors aged 60, 65, and 70 years had nuclear cataracts; additionally, the right eye lens only of the 60-year-old donor had a cortical cataract. In transparent lenses, the relative amounts of boundary plus trapped PLs increase monotonously with donor age, and, at all ages, this amount was greater in nuclear compared with cortical membranes. Moreover, in transparent lenses, the relative amount of trapped Chol increases with age in nuclear membranes. However, the EPR spectrum of ASL from cortical membranes of 15- to 60-year-old donors shows only the weakly immobilized component assigned to ASL in the bulk plus Chol bilayer domain. Only the cortical membranes of 61- to 70-year-old donors contain both weakly and strongly immobilized components. The strongly immobilized component is assigned to ASL in trapped lipids. We speculate that the age of 60 years may be considered as a "threshold" for appearance of trapped lipids in cortical membranes. The relative amounts of boundary plus trapped PLs in lenses with nuclear cataracts is lower than that predicted from the tendency of the age-dependent increase observed for transparent lenses. The differences in amounts of lipids in the indicated left and right eye domains of each donor are smaller than the differences in single donors of a similar age.
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Affiliation(s)
- Laxman Mainali
- Department of Physics, Boise State University, Boise, ID 83725, USA
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA
| | - Marija Raguz
- Department of Medical Physics and Biophysics, University of Split School of Medicine, 21000 Split, Croatia
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Subczynski WK, Widomska J, Raguz M, Pasenkiewicz-Gierula M. Molecular oxygen as a probe molecule in EPR spin-labeling studies of membrane structure and dynamics. OXYGEN (BASEL, SWITZERLAND) 2022; 2:295-316. [PMID: 36852103 PMCID: PMC9965258 DOI: 10.3390/oxygen2030021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Molecular oxygen (O2) is the perfect probe molecule for membrane studies carried out using the saturation recovery EPR technique. O2 is a small, paramagnetic, hydrophobic enough molecule that easily partitions into a membrane's different phases and domains. In membrane studies, the saturation recovery EPR method requires two paramagnetic probes: a lipid-analog nitroxide spin label and an oxygen molecule. The experimentally derived parameters of this method are the spin-lattice relaxation times (T 1s) of spin labels and rates of bimolecular collisions between O2 and the nitroxide fragment. Thanks to the long T 1 of lipid spin labels (from 1 to 10 μs), the approach is very sensitive to changes of the local (around the nitroxide fragment) O2 diffusion-concentration product. Small variations in the lipid packing affect O2 solubility and O2 diffusion, which can be detected by the shortening of T 1 of spin labels. Using O2 as a probe molecule and a different lipid spin label inserted into specific phases of the membrane and membrane domains allows data about the lateral arrangement of lipid membranes to be obtained. Moreover, using a lipid spin label with the nitroxide fragment attached to its head group or a hydrocarbon chain at different positions also enables data about molecular dynamics and structure at different membrane depths to be obtained. Thus, the method can be used to investigate not only the lateral organization of the membrane (i.e., the presence of membrane domains and phases), but also the depth-dependent membrane structure and dynamics, and, hence, the membrane properties in three dimensions.
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Affiliation(s)
- Witold K. Subczynski
- Department of Biophysics, Medical College on Wisconsin, Milwaukee, United States
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, Lublin, Poland
| | - Marija Raguz
- Department of Medical Physics and Biophysics, University of Split School of Medicine, Split, Croatia
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Subczynski WK, Widomska J, Stein N, Swartz HM. Factors determining barrier properties to oxygen transport across model and cell plasma membranes based on EPR spin-label oximetry. APPLIED MAGNETIC RESONANCE 2021; 52:1237-1260. [PMID: 36267674 PMCID: PMC9581439 DOI: 10.1007/s00723-021-01412-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Revised: 07/23/2021] [Accepted: 08/04/2021] [Indexed: 06/01/2023]
Abstract
This review is motivated by the exciting new area of radiation therapy using a phenomenon termed FLASH in which oxygen is thought to have a central role. Well-established principles of radiation biology and physics suggest that if oxygen has a strong role, it should be the level at the DNA. The key aspect discussed is the rate of oxygen diffusion. If oxygen freely diffuses into cells and rapidly equilibrates, then measurements in the extracellular compartment would enable FLASH to be investigated using existing methodologies that can readily measure oxygen in the extracellular compartment. EPR spin-label oximetry allows evaluation of the oxygen permeability coefficient across lipid bilayer membranes. It is established that simple fluid phase lipid bilayers are not barriers to oxygen transport. However, further investigations indicate that many physical and chemical (compositional) factor can significantly decrease this permeation. In biological cell plasma membranes, the lipid bilayer forms the matrix in which integral membrane proteins are immersed, changing organization and properties of the lipid matrix. To evaluate oxygen permeability coefficients across these complex membranes, oxygen permeation across all membrane domains and components must be considered. In this review, we consider many of the factors that affect (decrease) oxygen permeation across cell plasma membranes. Finally, we address the question, can the plasma membrane of the cell form a barrier to the free diffusion of oxygen into the cell interior? If there is a barrier then this must be considered in the investigations of the role of oxygen in FLASH.
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Affiliation(s)
- Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, Jaczewskiego 4, Lublin, Poland
| | - Natalia Stein
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - Harold M. Swartz
- Department of Radiology, The Geisel School of Medicine at Dartmouth, Lebanon, NH 03766, USA
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Fake It 'Till You Make It-The Pursuit of Suitable Membrane Mimetics for Membrane Protein Biophysics. Int J Mol Sci 2020; 22:ijms22010050. [PMID: 33374526 PMCID: PMC7793082 DOI: 10.3390/ijms22010050] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Revised: 12/17/2020] [Accepted: 12/19/2020] [Indexed: 12/13/2022] Open
Abstract
Membrane proteins evolved to reside in the hydrophobic lipid bilayers of cellular membranes. Therefore, membrane proteins bridge the different aqueous compartments separated by the membrane, and furthermore, dynamically interact with their surrounding lipid environment. The latter not only stabilizes membrane proteins, but directly impacts their folding, structure and function. In order to be characterized with biophysical and structural biological methods, membrane proteins are typically extracted and subsequently purified from their native lipid environment. This approach requires that lipid membranes are replaced by suitable surrogates, which ideally closely mimic the native bilayer, in order to maintain the membrane proteins structural and functional integrity. In this review, we survey the currently available membrane mimetic environments ranging from detergent micelles to bicelles, nanodiscs, lipidic-cubic phase (LCP), liposomes, and polymersomes. We discuss their respective advantages and disadvantages as well as their suitability for downstream biophysical and structural characterization. Finally, we take a look at ongoing methodological developments, which aim for direct in-situ characterization of membrane proteins within native membranes instead of relying on membrane mimetics.
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Avetisov KS, Bakhchieva NA, Avetisov SE, Novikov IA, Golovchenko AV, Shitikova AV. [Atomic force microscopy in the study of anterior eye segment structures]. Vestn Oftalmol 2020; 136:103-110. [PMID: 32241976 DOI: 10.17116/oftalma2020136011103] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The application of atomic force microscopy (AFM) in ophthalmology is considered with respect of the classical anatomical division of the eye into anterior and posterior segments. The review presents the findings of published research studies that involved AFM as a method for assessing anatomical and functional condition of the structures of anterior eye segment. One significant line of research is related to the use of AFM technologies for evaluation of morphological and biomechanical characteristics of various parts of the eye lens. That topic draws interest due to the need of furthering the understanding of cataractogenesis, as well as the significance of the anatomical and functional characteristics of the lens capsule in the mechanism of accommodation and modern phaco surgery.
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Affiliation(s)
- K S Avetisov
- Research Institute of Eye Disease, 11A Rossolimo St., Moscow, Russian Federation, 119021
| | - N A Bakhchieva
- Research Institute of Eye Disease, 11A Rossolimo St., Moscow, Russian Federation, 119021
| | - S E Avetisov
- Research Institute of Eye Disease, 11A Rossolimo St., Moscow, Russian Federation, 119021; I.M. Sechenov First Moscow State Medical University, Department of Ophthalmology, 8-2 Trubetskaya St., Moscow, Russian Federation, 119991
| | - I A Novikov
- Research Institute of Eye Disease, 11A Rossolimo St., Moscow, Russian Federation, 119021
| | - A V Golovchenko
- I.M. Sechenov First Moscow State Medical University, Department of Ophthalmology, 8-2 Trubetskaya St., Moscow, Russian Federation, 119991
| | - A V Shitikova
- International school 'Medicine of Future' of the Sechenov University, 8-2 Trubetskaya St., Moscow, Russian Federation, 119991
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Stein N, Mainali L, Hyde JS, Subczynski WK. Characterization of the distribution of spin-lattice relaxation rates of lipid spin labels in fiber cell plasma membranes of eye lenses with a stretched-exponential function. APPLIED MAGNETIC RESONANCE 2019; 50:903-918. [PMID: 31244509 PMCID: PMC6594395 DOI: 10.1007/s00723-019-01119-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Revised: 02/19/2019] [Indexed: 06/02/2023]
Abstract
The stretched exponential function (SEF) was used to analyze and interpret saturation recovery (SR) electron paramagnetic resonance (EPR) data obtained from spin-labeled porcine eye-lens membranes. This function has two fitting parameters: the characteristic spin-lattice relaxation rate (T 1str -1) and the stretching parameter (β), which ranges between zero and one. When β = 1, the function is a single exponential. It is assumed that the SEF arises from a distribution of single exponential functions, each described by a T 1 value. Because T 1 -1s are determined primarily by the rotational diffusion of spin labels, they are a measure of membrane fluidity. Since β describes the distribution of T 1 -1s, it can be interpreted as a measure of membrane heterogeneity. The SEF was used to analyze SR data obtained from intact cortical and nuclear fiber cell plasma membranes extracted from the eye lenses of two-year old animals and spinlabeled with phospholipid- and cholesterol-analogs. The lipid environment sensed by these probe molecules was found to be less fluid and more heterogeneous in nuclear membranes than in cortical membranes. Parameters T 1str -1 and β were also used for a multivariate K-means cluster analysis of stretched-exponential data. This analysis indicates that SEF data can be assigned accurately to clusters in nuclear or cortical membranes. In future work, the SEF will be applied to analyze data from human eye lenses of donors with differing health histories.
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Affiliation(s)
- Natalia Stein
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, USA
| | - Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, USA
| | - James S. Hyde
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, USA
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12
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Kumari S, Gao J, Mathias RT, Sun X, Eswaramoorthy A, Browne N, Zhang N, Varadaraj K. Aquaporin 0 Modulates Lens Gap Junctions in the Presence of Lens-Specific Beaded Filament Proteins. Invest Ophthalmol Vis Sci 2017; 58:6006-6019. [PMID: 29196765 PMCID: PMC5710632 DOI: 10.1167/iovs.17-22153] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose The objective of this study was to understand the molecular and physiologic mechanisms behind the lens cataract differences in Aquaporin 0-knockout-Heterozygous (AQP0-Htz) mice developed in C57 and FVB (lacks beaded filaments [BFs]) strains. Methods Lens transparency was studied using dark field light microscopy. Water permeability (Pf) was measured in fiber cell membrane vesicles. Western blotting/immunostaining was performed to verify expression of BF proteins and connexins. Microelectrode-based intact lens intracellular impedance was measured to determine gap junction (GJ) coupling resistance. Lens intracellular hydrostatic pressure (HP) was determined using a microelectrode/manometer system. Results Lens opacity and spherical aberration were more distinct in AQP0-Htz lenses from FVB than C57 strains. In either background, compared to wild type (WT), AQP0-Htz lenses showed decreased Pf (approximately 50%), which was restored by transgenic expression of AQP1 (TgAQP1/AQP0-Htz), but the opacities and differences between FVB and C57 persisted. Western blotting revealed no change in connexin expression levels. However, in C57 AQP0-Htz and TgAQP1/AQP0-Htz lenses, GJ coupling resistance decreased approximately 2.8-fold and the HP gradient decreased approximately 1.9-fold. Increased Pf in TgAQP1/AQP0-Htz did not alter GJ coupling resistance or HP. Conclusions In C57 AQP0-Htz lenses, GJ coupling resistance decreased. HP reduction was smaller than the coupling resistance reduction, a reflection of an increase in fluid circulation, which is one reason for the less severe cataract in C57 than FVB. Overall, our results suggest that AQP0 modulates GJs in the presence of BF proteins to maintain lens transparency and homeostasis.
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Affiliation(s)
- Sindhu Kumari
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States
| | - Junyuan Gao
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States
| | - Richard T Mathias
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States.,SUNY Eye Institute, Syracuse, New York, United States
| | - Xiurong Sun
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States
| | - Amizhdini Eswaramoorthy
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States
| | - Nicholas Browne
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States
| | - Nigel Zhang
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States
| | - Kulandaiappan Varadaraj
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York, United States.,SUNY Eye Institute, Syracuse, New York, United States
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13
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Cholesterol Bilayer Domains in the Eye Lens Health: A Review. Cell Biochem Biophys 2017; 75:387-398. [PMID: 28660427 PMCID: PMC5691107 DOI: 10.1007/s12013-017-0812-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 06/15/2017] [Indexed: 11/06/2022]
Abstract
The most unique biochemical characteristic of the eye lens fiber cell plasma membrane is its extremely high cholesterol content, the need for which is still unclear. It is evident, however, that the disturbance of Chol homeostasis may result in damages associated with cataracts. Electron paramagnetic resonance methods allow discrimination of two types of lipid domains in model membranes overloaded with Chol, namely, phospholipid-cholesterol domains and pure Chol bilayer domains. These domains are also detected in human lens lipid membranes prepared from the total lipids extracted from lens cortices and nuclei of donors from different age groups. Independent of the age-related changes in phospholipid composition, the physical properties of phospholipid-Chol domains remain the same for all age groups and are practically identical for cortical and nuclear membranes. The presence of Chol bilayer domains in these membranes provides a buffering capacity for cholesterol concentration in the surrounding phospholipid-Chol domains, keeping it at a constant saturating level and thus keeping the physical properties of the membrane consistent with and independent of changes in phospholipid composition. It seems that the presence of Chol bilayer domains plays an integral role in the regulation of cholesterol-dependent processes in fiber cell plasm membranes and in the maintenance of fiber cell membrane homeostasis.
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Mainali L, Raguz M, O’Brien WJ, Subczynski WK. Changes in the Properties and Organization of Human Lens Lipid Membranes Occurring with Age. Curr Eye Res 2017; 42:721-731. [PMID: 27791387 PMCID: PMC5409882 DOI: 10.1080/02713683.2016.1231325] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Revised: 08/01/2016] [Accepted: 08/28/2016] [Indexed: 10/20/2022]
Abstract
PURPOSE This research was undertaken to document the changes in the organization and properties of human lens lipid membranes that occur with age. METHODS Human lens lipid membranes prepared from the total lipids extracted from clear lens cortices and nuclei of donors from age groups 0-20 and 21-40 years were investigated. An electron paramagnetic resonance technique and nitroxide spin labels (analogues of phospholipids and cholesterol) were used. RESULTS Two distinct lipid domains, the phospholipid-cholesterol domain (PCD) and the pure cholesterol bilayer domain (CBD), were detected in all investigated membranes. Profiles of the acyl chain order, fluidity, hydrophobicity, and oxygen transport parameter across discriminated coexisting lipid domains were assessed. Independent of the age-related changes in phospholipid composition, the physical properties of the PCD remained the same for all age groups and were practically identical for cortical and nuclear membranes. However, the properties of pure CBDs changed significantly with the age of the donor and were related to the size of the CBD, which increased with the age of the donor and was greater in nuclear than in cortical membranes. A more detailed analysis revealed that the size of the CBD was determined mainly by the cholesterol content in the membrane. CONCLUSIONS This paper presents data from four age groups: 0-20, 21-40, 41-60, and 61-70 years. Data from age groups 41-60 and 61-70 years were published previously. Combining the previously published data with those data obtained in the present work allowed us to show the changes in the organization of cortical and nuclear lens lipid membranes as functions of age and cholesterol. It seems that the balance between age-related changes in membrane phospholipid composition and cholesterol content plays an integral role in the regulation of cholesterol-dependent processes in fiber cell membranes and in the maintenance of fiber cell membrane homeostasis.
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Affiliation(s)
- Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Marija Raguz
- Department of Medical Physics and Biophysics, School of Medicine, University of Split, Split, Croatia
| | - William J. O’Brien
- Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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Ricci M, Quinlan RA, Voïtchovsky K. Sub-nanometre mapping of the aquaporin-water interface using multifrequency atomic force microscopy. SOFT MATTER 2016; 13:187-195. [PMID: 27373564 DOI: 10.1039/c6sm00751a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Aquaporins are integral membrane proteins that regulate the transport of water and small molecules in and out of the cell. In eye lens tissue, circulation of water, ions and metabolites is ensured by a microcirculation system in which aquaporin-0 (AQP0) plays a central role. AQP0 allows water to flow beyond the diffusion limit through lens membranes. AQP0 naturally arranges in a square lattice. The malfunction of AQP0 is related to numerous diseases such as cataracts. Despite considerable research into its structure, function and dynamics, the interface between the protein and the surrounding liquid and the effect of the lattice arrangement on the behaviour of water at the interface with the membrane are still not fully understood. Here we use a multifrequency atomic force microscopy (AFM) approach to map both the liquid at the interface with AQP0 and the protein itself with sub-nanometer resolution. Imaging using the fundamental eigenmode of the AFM cantilever probes mainly the interfacial water at the surface of the membrane. The results highlight a well-defined region that surrounds AQP0 tetramers and where water exhibits a higher affinity for the protein. Imaging in the second eigenmode is dominated by the mechanical response of the protein and provides sub-molecular details of the protein surface and the sub-surface structure. The relationship between modes and harmonics is also examined.
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Affiliation(s)
- Maria Ricci
- Biological and Soft Systems, Cavendish Laboratory, Cambridge University, Cambridge, UK
| | - Roy A Quinlan
- School of Biological and Biomedical Sciences, Durham University, Durham, UK.
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Chen J, Zhou J, Wu J, Zhang G, Kang L, Ben J, Wang Y, Qin B, Guan H. Aberrant Epigenetic Alterations of Glutathione-S-Transferase P1 in Age-Related Nuclear Cataract. Curr Eye Res 2016; 42:402-410. [PMID: 27348130 DOI: 10.1080/02713683.2016.1185129] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- Jia Chen
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
| | - Jing Zhou
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
| | - Jian Wu
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
| | - Guowei Zhang
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
| | - Lihua Kang
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
| | - Jindong Ben
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
| | - Yong Wang
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
| | - Bai Qin
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
| | - Huaijin Guan
- Eye Institute, Affiliated Hospital of Nantong University, Nantong, China
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Amounts of phospholipids and cholesterol in lipid domains formed in intact lens membranes: Methodology development and its application to studies of porcine lens membranes. Exp Eye Res 2015; 140:179-186. [PMID: 26384651 DOI: 10.1016/j.exer.2015.09.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Revised: 08/29/2015] [Accepted: 09/14/2015] [Indexed: 11/22/2022]
Abstract
An electron paramagnetic resonance spin-labeling method has been developed that allows quantitative evaluation of the amounts of phospholipids and cholesterol in lipid domains of intact fiber-cell plasma membranes isolated from cortical and nuclear regions of eye lenses. The long term goal of this research is the assessment of organizational changes in human lens fiber cell membranes that occur with age and during cataract development. The measurements needed to be performed on lens membranes prepared from eyes of single donors and from single eyes. For these types of studies it is necessary to separate the age/cataract related changes from preparation/technique related changes. Human lenses differ not only because of age, but also because of the varying health histories of the donors. To solve these problems the sample-to-sample preparation/technique related changes were evaluated for cortical and nuclear lens membranes prepared from single porcine eyes. It was assumed that the differences due to the age (animals were two year old) and environmental conditions for raising these animals were minimal. Mean values and standard deviations from preparation/technique changes for measured amounts of lipids in membrane domains were calculated. Statistical analysis (Student's t-test) of the data also allowed determining the differences of mean values which were statistically significant with P ≤ 0.05. These differences defined for porcine lenses will be used for comparison of amounts of lipids in domains in human lens membranes prepared from eyes of single donors and from single eyes. Greater separations will indicate that differences were statistically significant with (P ≤ 0.05) and that they came from different than preparation/technique sources. Results confirmed that in nuclear porcine membranes the amounts of lipids in domains created due to the presence of membrane proteins were greater than those in cortical membranes and the differences were larger than the differences observed for human intact fiber cell membranes [Raguz, M. Mainali, L., O'Brien, W.J., and Subczynski, W.K. (2015) Exp. Eye Res.]. Lipids in porcine nuclear fiber cell plasma membranes were more rigid and less permeable to oxygen than in human nuclear membranes. Most likely the significant differences in the lipid composition were responsible for the observed differences.
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Hite RK, Chiu PL, Schuller JM, Walz T. Effect of lipid head groups on double-layered two-dimensional crystals formed by aquaporin-0. PLoS One 2015; 10:e0117371. [PMID: 25635393 PMCID: PMC4311914 DOI: 10.1371/journal.pone.0117371] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Accepted: 12/23/2014] [Indexed: 11/18/2022] Open
Abstract
Aquaporin-0 (AQP0) is a lens-specific water channel that also forms membrane junctions. Reconstitution of AQP0 with dimyristoyl phosphatidylcholine (DMPC) and E. coli polar lipids (EPL) yielded well-ordered, double-layered two-dimensional (2D) crystals that allowed electron crystallographic structure determination of the AQP0-mediated membrane junction. The interacting tetramers in the two crystalline layers are exactly in register, resulting in crystals with p422 symmetry. The high-resolution density maps also allowed modeling of the annular lipids surrounding the tetramers. Comparison of the DMPC and EPL bilayers suggested that the lipid head groups do not play an important role in the interaction of annular lipids with AQP0. We now reconstituted AQP0 with the anionic lipid dimyristoyl phosphatidylglycerol (DMPG), which yielded a mixture of 2D crystals with different symmetries. The different crystal symmetries result from shifts between the two crystalline layers, suggesting that the negatively charged PG head group destabilizes the interaction between the extracellular AQP0 surfaces. Reconstitution of AQP0 with dimyristoyl phosphatidylserine (DMPS), another anionic lipid, yielded crystals that had the usual p422 symmetry, but the crystals showed a pH-dependent tendency to stack through their cytoplasmic surfaces. Finally, AQP0 failed to reconstitute into membranes that were composed of more than 40% dimyristoyl phosphatidic acid (DMPA). Hence, although DMPG, DMPS, and DMPA are all negatively charged lipids, they have very different effects on AQP0 2D crystals, illustrating the importance of the specific lipid head group chemistry beyond its mere charge.
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Affiliation(s)
- Richard Kevin Hite
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Po-Lin Chiu
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Jan Michael Schuller
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Thomas Walz
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
- Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts, United States of America
- * E-mail:
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Raguz M, Mainali L, O'Brien WJ, Subczynski WK. Lipid domains in intact fiber-cell plasma membranes isolated from cortical and nuclear regions of human eye lenses of donors from different age groups. Exp Eye Res 2015; 132:78-90. [PMID: 25617680 DOI: 10.1016/j.exer.2015.01.018] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Revised: 01/05/2015] [Accepted: 01/20/2015] [Indexed: 02/02/2023]
Abstract
The results reported here clearly document changes in the properties and the organization of fiber-cell membrane lipids that occur with age, based on electron paramagnetic resonance (EPR) analysis of lens membranes of clear lenses from donors of age groups from 0 to 20, 21 to 40, and 61 to 80 years. The physical properties, including profiles of the alkyl chain order, fluidity, hydrophobicity, and oxygen transport parameter, were investigated using EPR spin-labeling methods, which also provide an opportunity to discriminate coexisting lipid domains and to evaluate the relative amounts of lipids in these domains. Fiber-cell membranes were found to contain three distinct lipid environments: bulk lipid domain, which appears minimally affected by membrane proteins, and two domains that appear due to the presence of membrane proteins, namely boundary and trapped lipid domains. In nuclear membranes the amount of boundary and trapped phospholipids as well as the amount of cholesterol in trapped lipid domains increased with the donors' age and was greater than that in cortical membranes. The difference between the amounts of lipids in domains uniquely formed due to the presence of membrane proteins in nuclear and cortical membranes increased with the donors' age. It was also shown that cholesterol was to a large degree excluded from trapped lipid domains in cortical membranes. It is evident that the rigidity of nuclear membranes was greater than that of cortical membranes for all age groups. The amount of lipids in domains of low oxygen permeability, mainly in trapped lipid domains, were greater in nuclear than cortical membranes and increased with the age of donors. These results indicate that the nuclear fiber cell plasma membranes were less permeable to oxygen than cortical membranes and become less permeable to oxygen with age. In clear lenses, age-related changes in the lens lipid and protein composition and organization appear to occur in ways that increase fiber cell plasma membrane resistance to oxygen permeation.
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Affiliation(s)
- Marija Raguz
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA; Department of Medical Physics and Biophysics, School of Medicine, University of Split, Split, Croatia
| | - Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - William J O'Brien
- Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Witold K Subczynski
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
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Kumari SS, Varadaraj K. Aquaporin 0 plays a pivotal role in refractive index gradient development in mammalian eye lens to prevent spherical aberration. Biochem Biophys Res Commun 2014; 452:986-91. [PMID: 25229686 DOI: 10.1016/j.bbrc.2014.09.032] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Accepted: 09/08/2014] [Indexed: 12/27/2022]
Abstract
Aquaporin 0 (AQP0) is a transmembrane channel that constitutes ∼45% of the total membrane protein of the fiber cells in mammalian lens. It is critical for lens transparency and homeostasis as mutations and knockout cause autosomal dominant lens cataract. AQP0 functions as a water channel and as a cell-to-cell adhesion (CTCA) molecule in the lens. Our recent in vitro studies showed that the CTCA function of AQP0 could be crucial to establish lens refractive index gradient (RING). However, there is a lack of in vivo data to corroborate the role of AQP0 as a fiber CTCA molecule which is critical for creating lens RING. The present investigation is undertaken to gather in vivo evidence for the involvement of AQP0 in developing lens RING. Lenses of wild type (WT) mouse, AQP0 knockout (heterozygous, AQP0(+/-)) and AQP0 knockout lens transgenically expressing AQP1 (heterozygous AQP0(+/)(-)/AQP1(+/)(-)) mouse models were used for the study. Data on AQP0 protein profile of intact and N- and/or C-terminal cleaved AQP0 in the lens by MALDI-TOF mass spectrometry and SDS-PAGE revealed that outer cortex fiber cells have only intact AQP0 of ∼28kDa, inner cortical and outer nuclear fiber cells have both intact and cleaved forms, and inner nuclear fiber cells have only cleaved forms (∼26-24kDa). Knocking out of 50% of AQP0 protein caused light scattering, spherical aberration (SA) and cataract. Restoring the lost fiber cell membrane water permeability (Pf) by transgene AQP1 did not reinstate complete lens transparency and the mouse lenses showed light scattering and SA. Transmission and scanning electron micrographs of lenses of both mouse models showed increased extracellular space between fiber cells. Water content determination study showed increase in water in the lenses of these mouse models. In summary, lens transparency, CTCA and compact packing of fiber cells were affected due to the loss of 50% AQP0 leading to larger extracellular space, more water content and SA, possibly due to alteration in RING. To our knowledge, this is the first report identifying the role of AQP0 in RING development to ward off lens SA during focusing.
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Affiliation(s)
- S Sindhu Kumari
- Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA
| | - Kulandaiappan Varadaraj
- Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA; SUNY Eye Institute, New York, NY, USA.
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21
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Eghiaian F, Rico F, Colom A, Casuso I, Scheuring S. High-speed atomic force microscopy: Imaging and force spectroscopy. FEBS Lett 2014; 588:3631-8. [DOI: 10.1016/j.febslet.2014.06.028] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Revised: 06/05/2014] [Accepted: 06/06/2014] [Indexed: 10/25/2022]
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Intact and N- or C-terminal end truncated AQP0 function as open water channels and cell-to-cell adhesion proteins: end truncation could be a prelude for adjusting the refractive index of the lens to prevent spherical aberration. Biochim Biophys Acta Gen Subj 2014; 1840:2862-77. [PMID: 24821012 DOI: 10.1016/j.bbagen.2014.05.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2013] [Revised: 04/30/2014] [Accepted: 05/02/2014] [Indexed: 11/20/2022]
Abstract
BACKGROUND Investigate the impact of natural N- or C-terminal post-translational truncations of lens mature fiber cell Aquaporin 0 (AQP0) on water permeability (Pw) and cell-to-cell adhesion (CTCA) functions. METHODS The following deletions/truncations were created by site-directed mutagenesis (designations in parentheses): Amino acid residues (AA) 2-6 (AQP0-N-del-2-6), AA235-263 (AQP0-1-234), AA239-263 (AQP0-1-238), AA244-263 (AQP0-1-243), AA247-263 (AQP0-1-246), AA250-263 (AQP0-1-249) and AA260-263 (AQP0-1-259). Protein expression was studied using immunostaining, fluorescent tags and organelle-specific markers. Pw was tested by expressing the respective complementary ribonucleic acid (cRNA) in Xenopus oocytes and conducting osmotic swelling assay. CTCA was assessed by transfecting intact or mutant AQP0 into adhesion-deficient L-cells and performing cell aggregation and adhesion assays. RESULTS AQP0-1-234 and AQP0-1-238 did not traffic to the plasma membrane. Trafficking of AQP0-N-del-2-6 and AQP0-1-243 was reduced causing decreased membrane Pw and CTCA. AQP0-1-246, AQP0-1-249 and AQP0-1-259 mutants trafficked properly and functioned normally. Pw and CTCA functions of the mutants were directly proportional to the respective amount of AQP0 expressed at the plasma membrane and remained comparable to those of intact AQP0 (AQP0-1-263). CONCLUSIONS Post-translational truncation of N- or C-terminal end amino acids does not alter the basal water permeability of AQP0 or its adhesive functions. AQP0 may play a role in adjusting the refractive index to prevent spherical aberration in the constantly growing lens. GENERAL SIGNIFICANCE Similar studies can be extended to other lens proteins which undergo post-translational truncations to find out how they assist the lens to maintain transparency and homeostasis for proper focusing of objects on to the retina.
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Ando T, Uchihashi T, Scheuring S. Filming biomolecular processes by high-speed atomic force microscopy. Chem Rev 2014; 114:3120-88. [PMID: 24476364 PMCID: PMC4076042 DOI: 10.1021/cr4003837] [Citation(s) in RCA: 239] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Indexed: 12/21/2022]
Affiliation(s)
- Toshio Ando
- Department of Physics, and Bio-AFM Frontier
Research Center, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
- CREST,
Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012, Japan
| | - Takayuki Uchihashi
- Department of Physics, and Bio-AFM Frontier
Research Center, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
- CREST,
Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012, Japan
| | - Simon Scheuring
- U1006
INSERM/Aix-Marseille Université, Parc Scientifique et Technologique
de Luminy Bâtiment Inserm TPR2 bloc 5, 163 avenue de Luminy, 13288 Marseille Cedex 9, France
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Lo WK, Biswas SK, Brako L, Shiels A, Gu S, Jiang JX. Aquaporin-0 targets interlocking domains to control the integrity and transparency of the eye lens. Invest Ophthalmol Vis Sci 2014; 55:1202-12. [PMID: 24458158 DOI: 10.1167/iovs.13-13379] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Lens fiber cell membranes contain aquaporin-0 (AQP0), which constitutes approximately 50% of the total fiber cell membrane proteins and has a dual function as a water channel protein and an adhesion molecule. Fiber cell membranes also develop an elaborate interlocking system that is required for maintaining structural order, stability, and lens transparency. Herein, we used an AQP0-deficient mouse model to investigate an unconventional adhesion role of AQP0 in maintaining a normal structure of lens interlocking protrusions. METHODS The loss of AQP0 in AQP0(-/-) lens fibers was verified by Western blot and immunofluorescence analyses. Changes in membrane surface structures of wild-type and AQP0(-/-) lenses at age 3 to 12 weeks were examined with scanning electron microscopy. Preferential distribution of AQP0 in wild-type fiber cell membranes was analyzed with immunofluorescence and immunogold labeling using freeze-fracturing transmission electron microscopy. RESULTS Interlocking protrusions in young differentiating fiber cells developed normally but showed minor abnormalities at approximately 50 μm deep in the absence of AQP0 in all ages studied. Strikingly, protrusions in maturing fiber cells specifically underwent uncontrolled elongation, deformation, and fragmentation, while cells still retained their overall shape. Later in the process, these changes eventually resulted in fiber cell separation, breakdown, and cataract formation in the lens core. Immunolabeling at the light microscopy and transmission electron microscopy levels demonstrated that AQP0 was particularly enriched in interlocking protrusions in wild-type lenses. CONCLUSIONS This study suggests that AQP0 exerts its primary adhesion or suppression role specifically to maintain the normal structure of interlocking protrusions that is critical to the integrity and transparency of the lens.
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Affiliation(s)
- Woo-Kuen Lo
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, Georgia
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25
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Raguz M, Mainali L, O'Brien WJ, Subczynski WK. Lipid-protein interactions in plasma membranes of fiber cells isolated from the human eye lens. Exp Eye Res 2014; 120:138-51. [PMID: 24486794 DOI: 10.1016/j.exer.2014.01.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 01/20/2014] [Accepted: 01/22/2014] [Indexed: 11/19/2022]
Abstract
The protein content in human lens membranes is extremely high, increases with age, and is higher in the nucleus as compared with the cortex, which should strongly affect the organization and properties of the lipid bilayer portion of intact membranes. To assess these effects, the intact cortical and nuclear fiber cell plasma membranes isolated from human lenses from 41- to 60-year-old donors were studied using electron paramagnetic resonance spin-labeling methods. Results were compared with those obtained for lens lipid membranes prepared from total lipid extracts from human eyes of the same age group [Mainali, L., Raguz, M., O'Brien, W. J., and Subczynski, W. K. (2013) Biochim. Biophys. Acta]. Differences were considered to be mainly due to the effect of membrane proteins. The lipid-bilayer portions of intact membranes were significantly less fluid than lipid bilayers of lens lipid membranes, prepared without proteins. The intact membranes were found to contain three distinct lipid environments termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain. However, the cholesterol bilayer domain, which was detected in cortical and nuclear lens lipid membranes, was not detected in intact membranes. The relative amounts of bulk and trapped lipids were evaluated. The amount of lipids in domains uniquely formed due to the presence of membrane proteins was greater in nuclear membranes than in cortical membranes. Thus, it is evident that the rigidity of nuclear membranes is greater than that of cortical membranes. Also the permeability coefficients for oxygen measured in domains of nuclear membranes were significantly lower than appropriate coefficients measured in cortical membranes. Relationships between the organization of lipids into lipid domains in fiber cells plasma membranes and the organization of membrane proteins are discussed.
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Affiliation(s)
- Marija Raguz
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA; Department of Medical Physics and Biophysics, School of Medicine, University of Split, Split, Croatia
| | - Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - William J O'Brien
- Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Witold K Subczynski
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
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26
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Pillet F, Chopinet L, Formosa C, Dague E. Atomic Force Microscopy and pharmacology: from microbiology to cancerology. Biochim Biophys Acta Gen Subj 2013; 1840:1028-50. [PMID: 24291690 DOI: 10.1016/j.bbagen.2013.11.019] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 11/18/2013] [Accepted: 11/20/2013] [Indexed: 02/06/2023]
Abstract
BACKGROUND Atomic Force Microscopy (AFM) has been extensively used to study biological samples. Researchers take advantage of its ability to image living samples to increase our fundamental knowledge (biophysical properties/biochemical behavior) on living cell surface properties, at the nano-scale. SCOPE OF REVIEW AFM, in the imaging modes, can probe cells morphological modifications induced by drugs. In the force spectroscopy mode, it is possible to follow the nanomechanical properties of a cell and to probe the mechanical modifications induced by drugs. AFM can be used to map single molecule distribution at the cell surface. We will focus on a collection of results aiming at evaluating the nano-scale effects of drugs, by AFM. Studies on yeast, bacteria and mammal cells will illustrate our discussion. Especially, we will show how AFM can help in getting a better understanding of drug mechanism of action. MAJOR CONCLUSIONS This review demonstrates that AFM is a versatile tool, useful in pharmacology. In microbiology, it has been used to study the drugs fighting Candida albicans or Pseudomonas aeruginosa. The major conclusions are a better understanding of the microbes' cell wall and of the drugs mechanism of action. In cancerology, AFM has been used to explore the effects of cytotoxic drugs or as an innovative diagnostic technology. AFM has provided original results on cultured cells, cells extracted from patient and directly on patient biopsies. GENERAL SIGNIFICANCE This review enhances the interest of AFM technologies for pharmacology. The applications reviewed range from microbiology to cancerology.
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Affiliation(s)
- Flavien Pillet
- CNRS, LAAS, 7 avenue du colonel Roche, F-31077 Toulouse Cedex 4, France; Université de Toulouse, UPS, INSA, INP, ISAE, UT1, UTM, LAAS, ITAV, F-31077 Toulouse Cedex 4, France
| | - Louise Chopinet
- CNRS, IPBS-UMR 5089, BP64182, 205 route de Narbonne, F-31077 Toulouse Cedex 4, France; Université de Toulouse, UPS, INSA, INP, ISAE, UT1, UTM, LAAS, ITAV, F-31077 Toulouse Cedex 4, France
| | - Cécile Formosa
- CNRS, LAAS, 7 avenue du colonel Roche, F-31077 Toulouse Cedex 4, France; Université de Toulouse, UPS, INSA, INP, ISAE, UT1, UTM, LAAS, ITAV, F-31077 Toulouse Cedex 4, France; CNRS, UMR 7565, SRSMC, Vandoeuvre-lès-Nancy, France; Université de Lorraine, UMR 7565, Faculté de Pharmacie, Nancy, France
| | - Etienne Dague
- CNRS, LAAS, 7 avenue du colonel Roche, F-31077 Toulouse Cedex 4, France; Université de Toulouse, UPS, INSA, INP, ISAE, UT1, UTM, LAAS, ITAV, F-31077 Toulouse Cedex 4, France; CNRS; ITAV-USR 3505; F31106 Toulouse, France.
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Duneau JP, Sturgis JN. Lateral organization of biological membranes. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2013; 42:843-50. [DOI: 10.1007/s00249-013-0933-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 09/13/2013] [Accepted: 09/26/2013] [Indexed: 11/24/2022]
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Kumari SS, Gandhi J, Mustehsan MH, Eren S, Varadaraj K. Functional characterization of an AQP0 missense mutation, R33C, that causes dominant congenital lens cataract, reveals impaired cell-to-cell adhesion. Exp Eye Res 2013; 116:371-85. [PMID: 24120416 DOI: 10.1016/j.exer.2013.09.019] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Revised: 09/13/2013] [Accepted: 09/30/2013] [Indexed: 01/25/2023]
Abstract
Aquaporin 0 (AQP0) performs dual functions in the lens fiber cells, as a water pore and as a cell-to-cell adhesion molecule. Mutations in AQP0 cause severe lens cataract in both humans and mice. An arginine to cysteine missense mutation at amino acid 33 (R33C) produced congenital autosomal dominant cataract in a Chinese family for five generations. We re-created this mutation in wild type human AQP0 (WT-AQP0) cDNA by site-directed mutagenesis, and cloned and expressed the mutant AQP0 (AQP0-R33C) in heterologous expression systems. Mutant AQP0-R33C showed proper trafficking and membrane localization like WT-AQP0. Functional studies conducted in Xenopus oocytes showed no significant difference (P > 0.05) in water permeability between AQP0-R33C and WT-AQP0. However, the cell-to-cell adhesion property of AQP0-R33C was significantly reduced (P < 0.001) compared to that of WT-AQP0, indicated by cell aggregation and cell-to-cell adhesion assays. Scrape-loading assay using Lucifer Yellow dye showed reduction in cell-to-cell adhesion affecting gap junction coupling (P < 0.001). The data provided suggest that this mutation might not have caused significant alterations in protein folding since there was no obstruction in protein trafficking or water permeation. Reduction in cell-to-cell adhesion and development of cataract suggest that the conserved positive charge of Extracellular Loop A may play an important role in bringing fiber cells closer. The proposed schematic models illustrate that cell-to-cell adhesion elicited by AQP0 is vital for lens transparency and homeostasis.
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Affiliation(s)
- Sindhu S Kumari
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA
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29
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A hybrid high-speed atomic force–optical microscope for visualizing single membrane proteins on eukaryotic cells. Nat Commun 2013; 4:2155. [DOI: 10.1038/ncomms3155] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Accepted: 06/17/2013] [Indexed: 11/08/2022] Open
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Tong J, Canty JT, Briggs MM, McIntosh TJ. The water permeability of lens aquaporin-0 depends on its lipid bilayer environment. Exp Eye Res 2013; 113:32-40. [PMID: 23680159 DOI: 10.1016/j.exer.2013.04.022] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2013] [Revised: 04/16/2013] [Accepted: 04/30/2013] [Indexed: 01/07/2023]
Abstract
Aquaporin-0 (AQP0), the primary water channel in lens fiber cells, is critical to lens development, organization, and function. In the avascular lens there is thought to be an internal microcirculation associated with fluid movement. Although AQP0 is known to be important in fluid fluxes across membranes, the water permeability of this channel has only been measured in Xenopus oocytes and in outer lens cortical membranes, but not in inner nuclear membranes, which have an increased cholesterol/phospholipid ratio. Here we measure the unit water permeability of AQP0 in different proteoliposomes with cholesterol/phospholipid ratios and external pHs similar to those found in the cortex and nucleus of the lens. Osmotic stress measurements were performed with proteoliposomes containing AQP0 and three different lipids mixtures: (1) phosphatidylcholine (PC) and phosphatidylglycerol (PG), (2) PC, PG, with 40 mol% cholesterol, and (3) sphingomyelin (SM), PG, with 40 mol% cholesterol. At pH 7.5 the unit permeabilities of AQP0 were 3.5 ± 0.5 × 10(-14) cm(3)/s (mean ± SEM), 1.1 ± 0.1 × 10(-14) cm(3)/s, and 0.50 ± 0.04 × 10(-14) cm(3)/s in PC:PG, PC:PG:cholesterol, and SM:PG:cholesterol, respectively. For lipid mixtures at pH 6.5, corresponding to conditions found in the lens nucleus, the AQP0 permeabilities were 1.5 ± 0.4 × 10(-14) cm(3)/s and 0.76 ± 0.03 × 10(-14) cm(3)/s in PC:PG:cholesterol and SM:PG:cholesterol, respectively. Thus, although AQP0 unit permeability can be modified by changes in pH, it is also sensitive to changes in bilayer lipid composition, and decreases with increasing cholesterol and SM content. These data imply that AQP0 water permeability is regulated by bilayer lipid composition, so that AQP0 permeability would be significantly less in the lens nucleus than in the lens cortex.
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Affiliation(s)
- Jihong Tong
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA
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31
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Liu LN, Scheuring S. Investigation of photosynthetic membrane structure using atomic force microscopy. TRENDS IN PLANT SCIENCE 2013; 18:277-86. [PMID: 23562040 DOI: 10.1016/j.tplants.2013.03.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Revised: 02/21/2013] [Accepted: 03/01/2013] [Indexed: 05/26/2023]
Abstract
Photosynthetic processes, including light capture, electron transfer, and energy conversion, are not only ensured by the activities of individual photosynthetic complexes but also substantially determined and regulated by the composition and assembly of the overall photosynthetic apparatus at the supramolecular level. In recent years, atomic force microscopy (AFM) has matured as a unique and powerful tool for directly assessing the supramolecular assembly of integral membrane protein complexes in their native membrane environment at submolecular resolution. This review highlights the major contributions and advances of AFM studies to our understanding of the structure of the bacterial photosynthetic machinery and its regulatory arrangement during chromatic adaptation. AFM topographs of other biological membrane systems and potential future applications of AFM are also discussed.
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Affiliation(s)
- Lu-Ning Liu
- Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK.
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Stewart DN, Lango J, Nambiar KP, Falso MJS, FitzGerald PG, Rocke DM, Hammock BD, Buchholz BA. Carbon turnover in the water-soluble protein of the adult human lens. Mol Vis 2013; 19:463-75. [PMID: 23441119 PMCID: PMC3580966] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Accepted: 02/21/2013] [Indexed: 12/02/2022] Open
Abstract
PURPOSE Human eye lenses contain cells that persist from embryonic development. These unique, highly specialized fiber cells located at the core (nucleus) of the lens undergo pseudo-apoptosis to become devoid of cell nuclei and most organelles. Ostensibly lacking in protein transcriptional capabilities, it is currently believed that these nuclear fiber cells owe their extreme longevity to the perseverance of highly stable and densely packed crystallin proteins. Maintaining the structural and functional integrity of lenticular proteins is necessary to sustain cellular transparency and proper vision, yet the means by which the lens actually copes with a lifetime of oxidative stress, seemingly without any capacity for protein turnover and repair, is not completely understood. Although many years of research have been predicated upon the assumption that there is no protein turnover or renewal in nuclear fiber cells, we investigated whether or not different protein fractions possess protein of different ages by using the (14)C bomb pulse. METHODS Adult human lenses were concentrically dissected by gently removing the cell layers in water or shaving to the nucleus with a curved micrometer-controlled blade. The cells were lysed, and the proteins were separated into water-soluble and water-insoluble fractions. The small molecules were removed using 3 kDa spin filters. The (14)C/C was measured in paired protein fractions by accelerator mass spectrometry, and an average age for the material within the sample was assigned using the (14)C bomb pulse. RESULTS The water-insoluble fractions possessed (14)C/C ratios consistent with the age of the cells. In all cases, the water-soluble fractions contained carbon that was younger than the paired water-insoluble fraction. CONCLUSIONS As the first direct evidence of carbon turnover in protein from adult human nuclear fiber cells, this discovery supports the emerging view of the lens nucleus as a dynamic system capable of maintaining homeostasis in part due to intricate protein transport mechanisms and possibly protein repair. This finding implies that the lens plays an active role in the aversion of age-related nuclear (ARN) cataract.
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Affiliation(s)
- Daniel N. Stewart
- Department of Chemistry, University of California, One Shields Avenue, Davis, CA
| | - Jozsef Lango
- Department of Chemistry, University of California, One Shields Avenue, Davis, CA
| | - Krishnan P. Nambiar
- Department of Chemistry, University of California, One Shields Avenue, Davis, CA
| | - Miranda J. S. Falso
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA,Currently Division of Math and Natural Sciences, Pennsylvania State University – Altoona, Altoona, PA
| | - Paul G. FitzGerald
- Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis, CA
| | - David M. Rocke
- Division of Biostatistics, School of Medicine, University of California, Davis, CA
| | - Bruce D. Hammock
- Department of Entomology and Comprehensive Cancer Center, University of California, One Shields Avenue, Davis, CA
| | - Bruce A. Buchholz
- Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA
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Baranovic J, Ramanujan CS, Kasai N, Midgett CR, Madden DR, Torimitsu K, Ryan JF. Reconstitution of homomeric GluA2(flop) receptors in supported lipid membranes: functional and structural properties. J Biol Chem 2013; 288:8647-8657. [PMID: 23382380 DOI: 10.1074/jbc.m112.422105] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
AMPA receptors (AMPARs) are glutamate-gated ion channels ubiquitous in the vertebrate central nervous system, where they mediate fast excitatory neurotransmission and act as molecular determinants of memory formation and learning. Together with detailed analyses of individual AMPAR domains, structural studies of full-length AMPARs by electron microscopy and x-ray crystallography have provided important insights into channel assembly and function. However, the correlation between the structure and functional states of the channel remains ambiguous particularly because these functional states can be assessed only with the receptor bound within an intact lipid bilayer. To provide a basis for investigating AMPAR structure in a membrane environment, we developed an optimized reconstitution protocol using a receptor whose structure has previously been characterized by electron microscopy. Single-channel recordings of reconstituted homomeric GluA2(flop) receptors recapitulate key electrophysiological parameters of the channels expressed in native cellular membranes. Atomic force microscopy studies of the reconstituted samples provide high-resolution images of membrane-embedded full-length AMPARs at densities comparable to those in postsynaptic membranes. The data demonstrate the effect of protein density on conformational flexibility and dimensions of the receptors and provide the first structural characterization of functional membrane-embedded AMPARs, thus laying the foundation for correlated structure-function analyses of the predominant mediators of excitatory synaptic signals in the brain.
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Affiliation(s)
- Jelena Baranovic
- Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom.
| | | | - Nahoko Kasai
- NTT Basic Research Laboratories, Atsugi, Kanagawa 243-0198, Japan
| | - Charles R Midgett
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755-1404
| | - Dean R Madden
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755-1404
| | | | - John F Ryan
- Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
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Levy D, Milhiet PE. Imaging of transmembrane proteins directly incorporated within supported lipid bilayers using atomic force microscopy. Methods Mol Biol 2013; 950:343-357. [PMID: 23086884 DOI: 10.1007/978-1-62703-137-0_19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Structural analysis of transmembrane proteins remains a challenge in biology, mainly due to their difficulty in being overexpressed and the required use of detergents that impair different steps of biochemistry classically used to obtain 3D crystals. In this context, we have developed a new technique for protein incorporation within supported lipid bilayers that only requires a few picomoles of protein per assay. Proteins are directly inserted into a detergent-destabilized bilayer that can be imaged in buffer with atomic force microscopy (AFM) allowing structural analysis down to sub-nanometer lateral resolution. In this chapter, we describe the main guidelines for this technique, from the choice of detergent to the requirements for AFM high-resolution imaging.
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35
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Aquaporins in drug discovery and pharmacotherapy. Mol Aspects Med 2012; 33:691-703. [DOI: 10.1016/j.mam.2012.01.002] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Revised: 01/13/2012] [Accepted: 01/15/2012] [Indexed: 11/18/2022]
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Colom A, Casuso I, Boudier T, Scheuring S. High-speed atomic force microscopy: cooperative adhesion and dynamic equilibrium of junctional microdomain membrane proteins. J Mol Biol 2012; 423:249-56. [PMID: 22796628 DOI: 10.1016/j.jmb.2012.07.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2012] [Revised: 06/29/2012] [Accepted: 07/03/2012] [Indexed: 11/29/2022]
Abstract
Junctional microdomains, paradigm for membrane protein segregation in functional assemblies, in eye lens fiber cell membranes are constituted of lens-specific aquaporin-0 tetramers (AQP0(4)) and connexin (Cx) hexamers, termed connexons. Both proteins have double function to assure nutrition and mediate adhesion of lens cells. Here we use high-speed atomic force microscopy to examine microdomain protein dynamics at the single-molecule level. We found that the adhesion function of head-to-head associated AQP0(4) and Cx is cooperative. This finding provides first experimental evidence for the mechanistic importance for junctional microdomain formation. From the observation of lateral association-dissociation events of AQP0(4), we determine that the enthalpic energy gain of a single AQP0(4)-AQP0(4) interaction in the membrane plane is -2.7 k(B)T, sufficient to drive formation of microdomains. Connexon association is stronger as dynamics are rarely observed, explaining their rim localization in junctional microdomains.
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Affiliation(s)
- Adai Colom
- U1006 INSERM, Aix-Marseille Université, Parc Scientifique de Luminy, Marseille F-13009, France
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37
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Pores of the toxin FraC assemble into 2D hexagonal clusters in both crystal structures and model membranes. J Struct Biol 2012; 180:312-7. [PMID: 22728830 DOI: 10.1016/j.jsb.2012.06.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 06/06/2012] [Accepted: 06/10/2012] [Indexed: 11/24/2022]
Abstract
The recent high-resolution structure of the toxin FraC derived from the sea anemone Actinia fragacea has provided new insight into the mechanism of pore formation by actinoporins. In this work, we report two new crystal forms of FraC in its oligomeric prepore conformation. Together with the previously reported structure, these two new structures reveal that ring-like nonamers of the toxin assemble into compact two-dimensional hexagonal arrays. This supramolecular organization is maintained in different relative orientations adopted by the oligomers within the crystal layers. Analyses of the aggregation of FraC pores in both planar and curved (vesicles) model membranes show similar 2D hexagonal arrangements. Our observations support a model in which hexagonal pore-packing is a clustering mechanism that maximizes toxin-driven membrane damage in the target cell.
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Mainali L, Raguz M, O'Brien WJ, Subczynski WK. Properties of fiber cell plasma membranes isolated from the cortex and nucleus of the porcine eye lens. Exp Eye Res 2012; 97:117-29. [PMID: 22326289 DOI: 10.1016/j.exer.2012.01.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2011] [Revised: 01/21/2012] [Accepted: 01/26/2012] [Indexed: 11/28/2022]
Abstract
The organization and physical properties of the lipid bilayer portion of intact cortical and nuclear fiber cell plasma membranes isolated from the eye lenses of two-year-old pigs were studied using electron paramagnetic resonance (EPR) spin-labeling. Membrane fluidity, hydrophobicity, and the oxygen transport parameter (OTP) were assessed from the EPR spectra of precisely positioned spin labels. Intact cortical and nuclear membranes, which include membrane proteins, were found to contain three distinct lipid environments. These lipid environments were termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain (lipids in protein aggregates). The amount of boundary and trapped lipids was greater in intact nuclear membranes than in cortical membranes. The properties of intact membranes were compared with the organization and properties of lens lipid membranes made of the total lipid extracts from the lens cortex or nucleus. In cortical lens lipid membranes, only one homogenous environment was detected, which was designated as a bulk lipid domain (phospholipid bilayer saturated with cholesterol). Lens lipid membranes prepared from the lens nucleus possessed two domains, assigned as a bulk lipid domain and a cholesterol bilayer domain (CBD). In intact nuclear membranes, it was difficult to discriminate the CBD, which was clearly detected in nuclear lens lipid membranes, because the OTP measured in the CBD is the same as in the domain formed by trapped lipids. The two domains unique to intact membranes-namely, the domain formed by boundary lipids and the domain formed by trapped lipids-were most likely formed due to the presence of membrane proteins. It is concluded that formation of rigid and practically impermeable domains is enhanced in the lens nucleus, indicating changes in membrane composition that may help to maintain low oxygen concentration in this lens region.
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Affiliation(s)
- Laxman Mainali
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
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39
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Sznee K, Dekker JP, Dame RT, van Roon H, Wuite GJL, Frese RN. Jumping mode atomic force microscopy on grana membranes from spinach. J Biol Chem 2011; 286:39164-71. [PMID: 21911498 DOI: 10.1074/jbc.m111.284844] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The thylakoid membrane system is a complex membrane system that organizes and reorganizes itself to provide plants optimal chemical energy from sunlight under different and varying environmental conditions. Grana membranes are part of this system and contain the light-driven water-splitting enzyme Photosystem II (PSII) and light-harvesting antenna complexes. Here, we present a direct visualization of PSII complexes within grana membranes from spinach. By means of jumping mode atomic force microscopy in liquid, minimal forces were applied between the scanning tip and membrane or protein, allowing complexes to be imaged with high detail. We observed four different packing arrangements of PSII complexes, which occur primarily as dimers: co-linear crystalline rows, nanometric domains of straight or skewed rows, and disordered domains. Upon storing surface-adhered membranes at low temperature prior to imaging, large-scale reorganizations of supercomplexes between PSII and light-harvesting complex II could be induced. The highest resolution images show the existence of membrane domains without obvious topography extending beyond supercomplexes. These observations illustrate the possibility for diffusion of proteins and smaller molecules within these densely packed membranes.
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Affiliation(s)
- Kinga Sznee
- Faculty of Sciences, Department of Physics and Astronomy, VU University Amsterdam, 1081 HV Amsterdam, The Netherlands
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40
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ATP synthase superassemblies in animals and plants: Two or more are better. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1807:1185-97. [PMID: 21679683 DOI: 10.1016/j.bbabio.2011.05.023] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Revised: 05/30/2011] [Accepted: 05/31/2011] [Indexed: 12/11/2022]
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41
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Two-dimensional kinetics of inter-connexin interactions from single-molecule force spectroscopy. J Mol Biol 2011; 412:72-9. [PMID: 21802430 DOI: 10.1016/j.jmb.2011.07.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Revised: 07/07/2011] [Accepted: 07/11/2011] [Indexed: 11/23/2022]
Abstract
Gap junction channels are intercellular channels that form by docking the extracellular loops of connexin protein subunits. While the structure and function of gap junctions as intercellular channels have been characterized using different techniques, the physics of the inter-connexin interaction remain unknown. Moreover, as far as we know, the capacity of gap junction channels to work as adhesion complexes supporting pulling forces has not yet been quantitatively addressed. We report the first quantitative characterization of the kinetics and binding strength of the interaction of a short peptide mimicking extracellular loop 2 of Cx26 with membrane-reconstituted Cx26, combining the imaging and force spectroscopy capabilities of atomic force microscopy. The fast dissociation rate inferred a dynamic bond, while the slow association rate reflected the reduced flexibility and small size of extracellular loops. Our results propose the gap junction channel as an adhesion complex that associates slowly and dissociates fast at low force but is able to support important pulling forces in its native, hexameric form.
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42
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Bassnett S, Shi Y, Vrensen GFJM. Biological glass: structural determinants of eye lens transparency. Philos Trans R Soc Lond B Biol Sci 2011; 366:1250-64. [PMID: 21402584 PMCID: PMC3061108 DOI: 10.1098/rstb.2010.0302] [Citation(s) in RCA: 231] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The purpose of the lens is to project a sharply focused, undistorted image of the visual surround onto the neural retina. The first pre-requisite, therefore, is that the tissue should be transparent. Despite the presence of remarkably high levels of protein, the lens cytosol remains transparent as a result of short-range-order interactions between the proteins. At a cellular level, the programmed elimination of nuclei and other light-scattering organelles from cells located within the pupillary space contributes directly to tissue transparency. Scattering at the cell borders is minimized by the close apposition of lens fibre cells facilitated by a plethora of adhesive proteins, some expressed only in the lens. Similarly, refractive index matching between lens membranes and cytosol is believed to minimize scatter. Refractive index matching between the cytoplasm of adjacent cells is achieved through the formation of cellular fusions that allow the intermingling of proteins. Together, these structural adaptations serve to minimize light scatter and enable this living, cellular structure to function as 'biological glass'.
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Affiliation(s)
- Steven Bassnett
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St Louis, MO, USA
| | - Yanrong Shi
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St Louis, MO, USA
| | - Gijs F. J. M. Vrensen
- Department of Ophthalmology, Leiden University Medical Center, Leiden, The Netherlands
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Buzhynskyy N, Salesse C, Scheuring S. Rhodopsin is spatially heterogeneously distributed in rod outer segment disk membranes. J Mol Recognit 2011; 24:483-9. [DOI: 10.1002/jmr.1086] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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44
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Casuso I, Rico F, Scheuring S. Biological AFM: where we come from - where we are - where we may go. J Mol Recognit 2011; 24:406-13. [DOI: 10.1002/jmr.1081] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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45
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Casuso I, Sens P, Rico F, Scheuring S. Experimental evidence for membrane-mediated protein-protein interaction. Biophys J 2011; 99:L47-9. [PMID: 20923630 DOI: 10.1016/j.bpj.2010.07.028] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2010] [Revised: 07/12/2010] [Accepted: 07/14/2010] [Indexed: 12/27/2022] Open
Abstract
Membrane proteins diffuse within the membrane, form oligomers and supramolecular assemblies. Using high-speed atomic force microscopy, we present direct experimental measure of an in-membrane-plane interaction potential between membrane proteins. In purple membranes, ATP-synthase c-rings formed dimers that temporarily dissociated. C-ring dimers revealed subdiffusive motion, while dissociated monomers diffused freely. C-rings center-to-center distance probability distribution allowed the calculation and modeling of an in-membrane-plane energy landscape that presented repulsion at 80 Å, most stable dimer association at 103 Å (-3.5 k(B)T strength), and dissociation at 125 Å (-1 k(B)T strength). This first experimental data of nonlabeled membrane protein diffusion and the corresponding in-membrane-plane interaction energy landscape characterized membrane protein interaction with an attractive range of several k(B)T that reaches to a radius of ∼50 Å within the membrane plane.
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46
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Last JA, Russell P, Nealey PF, Murphy CJ. The applications of atomic force microscopy to vision science. Invest Ophthalmol Vis Sci 2011; 51:6083-94. [PMID: 21123767 DOI: 10.1167/iovs.10-5470] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The atomic force microscope (AFM) is widely used in materials science and has found many applications in biological sciences but has been limited in use in vision science. The AFM can be used to image the topography of soft biological materials in their native environments. It can also be used to probe the mechanical properties of cells and extracellular matrices, including their intrinsic elastic modulus and receptor-ligand interactions. In this review, the operation of the AFM is described along with a review of how it has been thus far used in vision science. It is hoped that this review will serve to stimulate vision scientists to consider incorporating AFM as part of their research toolkit.
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Affiliation(s)
- Julie A Last
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
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47
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Liu J, Xu J, Gu S, Nicholson BJ, Jiang JX. Aquaporin 0 enhances gap junction coupling via its cell adhesion function and interaction with connexin 50. J Cell Sci 2010; 124:198-206. [PMID: 21172802 DOI: 10.1242/jcs.072652] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Both connexin 50 (Cx50) and aquaporin 0 (AQP0) have important roles in lens development and homeostasis, and their mutations are associated with human congenital cataracts. We have previously shown that Cx50 directly interacts with AQP0. Here, we demonstrate the importance of the Cx50 intracellular loop (IL) domain in mediating the interaction with AQP0 in the lens in vivo. AQP0 significantly increased (~20-30%) the intercellular coupling and conductance of Cx50 gap junctions. However, this increase was not observed when the IL domain was replaced with those from other lens connexins. The Cx50-AQP0 interaction had no effect on Cx50 hemichannel function. A fusion protein containing three extracellular loop domains of AQP0 efficiently blocked the cell-to-cell adhesion of AQP0 and attenuated the stimulatory effect of AQP0 on Cx50 gap junction conductance. These data suggest that the specific interaction between Cx50 and AQP0 enhances the coupling of Cx50 gap junctions, but not hemichannels, through the cell adhesion function of AQP0. This result establishes a physiological role of AQP0 in the functional regulation of gap junction channels.
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Affiliation(s)
- Jialu Liu
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, TX 78229-3900, USA
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Hite RK, Li Z, Walz T. Principles of membrane protein interactions with annular lipids deduced from aquaporin-0 2D crystals. EMBO J 2010; 29:1652-8. [PMID: 20389283 PMCID: PMC2876970 DOI: 10.1038/emboj.2010.68] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Accepted: 03/23/2010] [Indexed: 12/03/2022] Open
Abstract
We have previously described the interactions of aquaporin-0 (AQP0) with dimyristoyl phosphatidylcholine (DMPC) lipids. We have now determined the 2.5 Å structure of AQP0 in two-dimensional (2D) crystals formed with Escherichia coli polar lipids (EPLs), which differ from DMPC both in headgroups and acyl chains. Comparison of the two structures shows that AQP0 does not adapt to the different length of the acyl chains in EPLs and that the distance between the phosphodiester groups in the two leaflets of the DMPC and EPL bilayers is almost identical. The EPL headgroups interact differently with AQP0 than do those of DMPC, but the acyl chains in the EPL and DMPC bilayers occupy similar positions. The interactions of annular lipids with membrane proteins seem to be driven by the propensity of the acyl chains to fill gaps in the protein surface. Interactions of the lipid headgroups may be responsible for the specific interactions found in tightly bound lipids but seem to have a negligible effect on interactions of generic annular lipids with membrane proteins.
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Affiliation(s)
- Richard K Hite
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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Crane JM, Verkman AS. Reversible, temperature-dependent supramolecular assembly of aquaporin-4 orthogonal arrays in live cell membranes. Biophys J 2010; 97:3010-8. [PMID: 19948131 DOI: 10.1016/j.bpj.2009.09.017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Revised: 09/01/2009] [Accepted: 09/09/2009] [Indexed: 10/20/2022] Open
Abstract
The shorter "M23" isoform of the glial cell water channel aquaporin-4 (AQP4) assembles into orthogonal arrays of particles (OAPs) in cell plasma membranes, whereas the full-length "M1" isoform does not. N-terminal residues are responsible for OAP formation by AQP4-M23 and for blocking of OAP formation in AQP4-M1. In investigating differences in OAP formation by certain N-terminus mutants of AQP4, as measured by freeze-fracture electron microscopy versus live-cell imaging, we discovered reversible, temperature-dependent OAP assembly of certain weakly associating AQP4 mutants. Single-particle tracking of quantum-dot-labeled AQP4 in live cells and total internal reflection fluorescence microscopy showed >80% of M23 in OAPs at 10-50 degrees C compared to <10% of M1. However, OAP formation by N-terminus cysteine-substitution mutants of M1, which probe palmitoylation-regulated OAP assembly, was strongly temperature-dependent, increasing from <10% at 37 degrees C to >70% at 10 degrees C for the double mutant M1-C13A/C17A. OAP assembly by this mutant, but not by native M23, could also be modulated by reducing its membrane density. Exposure of native M1 and single cysteine mutants to 2-bromopalmitate confirmed the presence of regulated OAP assembly by S-palmitoylation. Kinetic studies showed rapid and reversible OAP formation during cooling and OAP disassembly during heating. Our results provide what to our knowledge is the first information on the energetics of AQP4 OAP assembly in plasma membranes.
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Affiliation(s)
- Jonathan M Crane
- Department of Medicine, Cardiovascular Research Institute, University of California, San Francisco, California, USA
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Vuong N, Baenziger JE, Johnston LJ. Preparation of reconstituted acetylcholine receptor membranes suitable for AFM imaging of lipid–protein interactions. Chem Phys Lipids 2010; 163:117-26. [DOI: 10.1016/j.chemphyslip.2009.09.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2009] [Revised: 09/04/2009] [Accepted: 09/24/2009] [Indexed: 12/20/2022]
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