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Niina T, Fuchigami S, Takada S. Flexible Fitting of Biomolecular Structures to Atomic Force Microscopy Images via Biased Molecular Simulations. J Chem Theory Comput 2020; 16:1349-1358. [PMID: 31909999 DOI: 10.1021/acs.jctc.9b00991] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
High-speed (HS) atomic force microscopy (AFM) is a prominent imaging technology that observes large-scale structural dynamics of biomolecules near the physiological condition, but the AFM data are limited to the surface shape of specimens. Rigid-body fitting methods were developed to obtain molecular structures that fit to an AFM image, without accounting for conformational changes. Here, we developed a method to fit flexibly a three-dimensional (3D) biomolecular structure into an AFM image. First, we describe a method to produce a pseudo-AFM image from a given 3D structure in a differentiable form. Then, using a correlation function between the experimental AFM image and the computational pseudo-AFM image, we developed a flexible fitting molecular dynamics (MD) simulation method by which we obtain protein structures that well fit to the given AFM image. We first test it with a twin experiment; using an AFM image produced from a protein structure different from its native conformation as a reference, we performed the flexible fitting MD simulations to sample conformations that fit well the reference AFM image, and the method was confirmed to work well. Then, parameter dependence in the protocol was discussed. Finally, we applied the method to a real experimental HS-AFM image for a flagellar protein FlhA, demonstrating its applicability. We also test the rigid-body fitting of a molecular structure to an AFM image. Our method will be a general tool for dynamic structure modeling based on HS-AFM images and is publicly available through the CafeMol software.
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Affiliation(s)
- Toru Niina
- Department of Biophysics, Graduate School of Science , Kyoto University , Kyoto 606-8502 , Japan
| | - Sotaro Fuchigami
- Department of Biophysics, Graduate School of Science , Kyoto University , Kyoto 606-8502 , Japan
| | - Shoji Takada
- Department of Biophysics, Graduate School of Science , Kyoto University , Kyoto 606-8502 , Japan
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Varadaraj K, Gao J, Mathias RT, Kumari S. C-Terminal End of Aquaporin 0 Regulates Lens Gap Junction Channel Function. Invest Ophthalmol Vis Sci 2019; 60:2525-2531. [PMID: 31195409 PMCID: PMC6568327 DOI: 10.1167/iovs.19-26787] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 05/09/2019] [Indexed: 11/24/2022] Open
Abstract
Purpose We reported previously that aquaporin 0 (AQP0) modulates lens fiber cell gap junction (GJ) channel function. The present study was conducted to find out whether the C-terminal end of AQP0 is involved in this regulation. Methods A mouse model, AQP0ΔC/ΔC, was genetically engineered to express AQP0 with 1-246 amino acids, without the normal intact AQP0 (1-263 amino acids) in the lens. Transparency and focusing of the lens were assessed. Intracellular impedance was measured to determine GJ coupling resistance. Intracellular hydrostatic pressure (HP) was also determined. Western blotting was performed to determine connexin (Cx46 and Cx50) expression levels. Results At postnatal day 10, AQP0ΔC/ΔC mouse lenses relative to age-matched wild-type lenses showed loss of transparency and abnormal optical distortion; GJ coupling resistance increased in the differentiating (1.6-fold) and mature (8-fold) fiber cells; lens HP increased approximately 1.5-fold at the junction between the differentiating and mature fiber cells and approximately 2.0-fold in the center; there was no significant change (P > 0.05) in expression levels of Cx46 or Cx50. Conclusions The increase in GJ coupling resistance was not associated with reduced connexin expression, suggesting either a reduction in the open probability or some physical change in plaque location. The increase in resistance was significantly greater than the increase in HP, suggesting less pressure-driven water flow through each open GJ channel. These changes may lead to a loss of transparency and abnormal optical distortion. Overall, our data demonstrate the C-terminal end of AQP0 is involved in modulating GJ coupling to maintain lens transparency and homeostasis.
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Affiliation(s)
- Kulandaiappan Varadaraj
- Physiology and Biophysics, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York, United States
| | - Junyuan Gao
- Physiology and Biophysics, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York, United States
| | - Richard T. Mathias
- Physiology and Biophysics, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York, United States
| | - Sindhu Kumari
- Physiology and Biophysics, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York, United States
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Kumari S, Taginik G, Varadaraj S, Varadaraj K. Positively charged amino acid residues in the extracellular loops A and C of lens aquaporin 0 interact with the negative charges in the plasma membrane to facilitate cell-to-cell adhesion. Exp Eye Res 2019; 185:107682. [PMID: 31150637 DOI: 10.1016/j.exer.2019.05.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2018] [Revised: 04/17/2019] [Accepted: 05/27/2019] [Indexed: 01/12/2023]
Abstract
This investigation was undertaken to find out whether the positive charges in the Extracellular Loops A (ELA) and C (ELC) of Aquaporin 0 (AQP0) are involved in lens fiber cell-to-cell adhesion (CTCA), and the possible mechanism of CTCA. AQP0 ELA or ELC was substituted with the corresponding AQP1 loop via Polymerase Chain Reaction. Positively charged arginine (R) and histidine (H) of mouse AQP0 ELA and ELC were substituted individually with glutamine (Q) to create R33Q, H40Q, R113Q and H122Q by mutagenesis. cRNA expression, immunostaining, Förster Resonance Energy Transfer (FRET) studies and protein analyses showed localization of all mutants except AQP0-AQP1ELC chimera (AQP0 ELC substituted with AQP1 ELC) at the plasma membrane. Osmotic Swelling Assay revealed comparable water permeability (Pf) among AQP0-AQP1ELA, R33Q, R113Q, and WT. CTCA assay demonstrated a significant reduction in adhesion in all mutants compared to the WT (14-73%) suggesting the importance of the conserved positively charged residues of ELA and ELC for adhesion. Studies involving AQP0-transfected L-cells, and lipid vesicles indicated that CTCA was due to the electrostatic interaction between the positively charged amino acids of AQP0 extracellular loops and the negative charges of the plasma membrane. Schematic models are provided to illustrate the mechanism.
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Affiliation(s)
- Sindhu Kumari
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, 11794-8661, USA
| | - Gozde Taginik
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, 11794-8661, USA
| | - Sangeeth Varadaraj
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, 11794-8661, USA
| | - Kulandaiappan Varadaraj
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, 11794-8661, USA; SUNY Eye Institute, New York, NY, USA.
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Varadaraj K, Kumari SS. Molecular mechanism of Aquaporin 0-induced fiber cell to fiber cell adhesion in the eye lens. Biochem Biophys Res Commun 2018; 506:284-289. [PMID: 30348525 DOI: 10.1016/j.bbrc.2018.10.066] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 10/10/2018] [Indexed: 01/16/2023]
Abstract
Cell-to-cell adhesion (CTCA), which is key for establishing lens transparency, is a critical function of Aquaporin 0 (AQP0). The aim of this investigation was to find out the possible mechanism by which AQP0 exerts CTCA between fiber cells, since there are two proposals currently, either an AQP0-AQP0 interaction or an AQP0-lipid interaction. We studied the mechanism of AQP0-induced CTCA in intact AQP0 and C-terminally cleaved AQP0 (CTC-AQP0). Assays showed CTCA between L-cells transfected with intact AQP0 or CTC-AQP0 and parental L-cells indicating AQP0-membrane interaction. Both forms of AQP0 significantly (P < 0.001) promoted adhesion to negatively charged l-α-phosphatidylserine lipid vesicles signifying AQP0-lipid interaction. AQP0-expressing L-cells also promoted adhesion of WT and AQP0-KO mouse lens fiber cell membrane vesicles (FCMVs) significantly (P < 0.001). However, when FCMVs of WT or AQP0-KO were plated over parental L-cells, only WT vesicles adhered significantly, corroborating AQP0-membrane interaction. After incubating with extracellular domain-specific AQP0 antibody, L-cells expressing intact AQP0 or CTC-AQP0 showed a significant reduction (P < 0.001) in the adhesion of AQP0-KO FCMVs indicating extracellular loop involvement in CTCA. WT FCMVs from outer cortex and inner cortex promoted adhesion to parental L-cells, without any statistically significant difference in adhesion efficiency (P > 0.05). Ultrastructure studies of WT, AQP0-KO and transgenic lenses showed AQP0 is critical for fiber CTCA and compaction. The data collected clearly demonstrate that the positively charged amino acids in the AQP0 extracellular loop domains interact with the negatively charged lipids in the plasma membrane to promote CTCA for compaction of fiber cells.
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Affiliation(s)
- Kulandaiappan Varadaraj
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA; SUNY Eye Institute, New York, NY, USA.
| | - S Sindhu Kumari
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA
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An iris diaphragm mechanism to gate a cyclic nucleotide-gated ion channel. Nat Commun 2018; 9:3978. [PMID: 30266906 PMCID: PMC6162275 DOI: 10.1038/s41467-018-06414-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Accepted: 09/04/2018] [Indexed: 12/21/2022] Open
Abstract
Cyclic nucleotide-gated (CNG) ion channels are non-selective cation channels key to signal transduction. The free energy difference of cyclic-nucleotide (cAMP/cGMP) binding/unbinding is translated into mechanical work to modulate the open/closed probability of the pore, i.e., gating. Despite the recent advances in structural determination of CNG channels, the conformational changes associated with gating remain unknown. Here we examine the conformational dynamics of a prokaryotic homolog of CNG channels, SthK, using high-speed atomic force microscopy (HS-AFM). HS-AFM of SthK in lipid bilayers shows that the CNBDs undergo dramatic conformational changes during the interconversion between the resting (apo and cGMP) and the activated (cAMP) states: the CNBDs approach the membrane and splay away from the 4-fold channel axis accompanied by a clockwise rotation with respect to the pore domain. We propose that these movements may be converted by the C-linker to pull the pore helices open in an iris diaphragm-like mechanism. Cyclic nucleotide-gated (CNG) ion channels are non-selective cation channels key to signal transduction, but conformational changes associated with gating remained unknown. Here authors use high-speed atomic force microscopy to visualize SthK channels dynamics in response to cyclic nucleotides.
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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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Sutka M, Amodeo G, Ozu M. Plant and animal aquaporins crosstalk: what can be revealed from distinct perspectives. Biophys Rev 2017; 9:545-562. [PMID: 28871493 DOI: 10.1007/s12551-017-0313-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Accepted: 08/02/2017] [Indexed: 01/03/2023] Open
Abstract
Aquaporins (AQPs) can be revisited from a distinct and complementary perspective: the outcome from analyzing them from both plant and animal studies. (1) The approach in the study. Diversity found in both kingdoms contrasts with the limited number of crystal structures determined within each group. While the structure of almost half of mammal AQPs was resolved, only a few were resolved in plants. Strikingly, the animal structures resolved are mainly derived from the AQP2-lineage, due to their important roles in water homeostasis regulation in humans. The difference could be attributed to the approach: relevance in animal research is emphasized on pathology and in consequence drug screening that can lead to potential inhibitors, enhancers and/or regulators. By contrast, studies on plants have been mainly focused on the physiological role that AQPs play in growth, development and stress tolerance. (2) The transport capacity. Besides the well-described AQPs with high water transport capacity, large amount of evidence confirms that certain plant AQPs can carry a large list of small solutes. So far, animal AQP list is more restricted. In both kingdoms, there is a great amount of evidence on gas transport, although there is still an unsolved controversy around gas translocation as well as the role of the central pore of the tetramer. (3) More roles than expected. We found it remarkable that the view of AQPs as specific channels has evolved first toward simple transporters to molecules that can experience conformational changes triggered by biochemical and/or mechanical signals, turning them also into signaling components and/or behave as osmosensor molecules.
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Affiliation(s)
- Moira Sutka
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires e Instituto de Biodiversidad y Biología Experimental, Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Gabriela Amodeo
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires e Instituto de Biodiversidad y Biología Experimental, Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina.
| | - Marcelo Ozu
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires e Instituto de Biodiversidad y Biología Experimental, Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina.
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8
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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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Chauvigné F, Fjelldal PG, Cerdà J, Finn RN. Auto-Adhesion Potential of Extraocular Aqp0 during Teleost Development. PLoS One 2016; 11:e0154592. [PMID: 27153052 PMCID: PMC4859563 DOI: 10.1371/journal.pone.0154592] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 04/17/2016] [Indexed: 11/25/2022] Open
Abstract
AQP0 water channels are the most abundant proteins expressed in the mammalian lens fiber membranes where they are essential for lens development and transparency. Unlike other aquaporin paralogs, mammalian AQP0 has a low intrinsic water permeability, but can form cell-to-cell junctions between the lens fibers. It is not known whether the adhesive properties of AQP0 is a derived feature found only in mammals, or exists as a conserved ancestral trait in non-mammalian vertebrates. Here we show that a tetraploid teleost, the Atlantic salmon, expresses four Aqp0 paralogs in the developing lens, but also expresses significant levels of aqp0 mRNAs and proteins in the epithelia of the pronephros, presumptive enterocytes, gill filament and epidermis. Quantitative PCR reveals that aqp0 mRNA titres increase by three orders of magnitude between the onset of somitogenesis and pigmentation of the eye. Using in situ hybridization and specific antisera, we show that at least two of the channels (Aqp0a1, -0b1 and/or -0b2) are localized in the extraocular basolateral and apical membranes, while Aqp0a2 is lens-specific. Heterologous expression of the Aqp0 paralogs in adhesion-deficient mouse fibolast L-cells reveals that, as for human AQP0, each intact salmon channel retains cell-to-cell adhesive properties. The strongest Aqp0 interactions are auto-adhesion, suggesting that homo-octamers likely form the intercellular junctions of the developing lens and epithelial tissues. The present data are thus the first to show the adhesion potential of Aqp0 channels in a non-mammalian vertebrate, and further uncover a novel extraocular role of the channels during vertebrate development.
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Affiliation(s)
- François Chauvigné
- Department of Biology, Bergen High Technology Centre, University of Bergen, 5020 Bergen, Norway
- Institute of Marine Research, Nordnes, 5817 Bergen, Norway
- * E-mail: (RNF); (FC)
| | | | - Joan Cerdà
- Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), 08003 Barcelona, Spain
| | - Roderick Nigel Finn
- Department of Biology, Bergen High Technology Centre, University of Bergen, 5020 Bergen, Norway
- Institute of Marine Research, Nordnes, 5817 Bergen, Norway
- * E-mail: (RNF); (FC)
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Kitchen P, Day RE, Salman MM, Conner MT, Bill RM, Conner AC. Beyond water homeostasis: Diverse functional roles of mammalian aquaporins. Biochim Biophys Acta Gen Subj 2015; 1850:2410-21. [PMID: 26365508 DOI: 10.1016/j.bbagen.2015.08.023] [Citation(s) in RCA: 106] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Revised: 08/25/2015] [Accepted: 08/30/2015] [Indexed: 01/02/2023]
Abstract
BACKGROUND Aquaporin (AQP) water channels are best known as passive transporters of water that are vital for water homeostasis. SCOPE OF REVIEW AQP knockout studies in whole animals and cultured cells, along with naturally occurring human mutations suggest that the transport of neutral solutes through AQPs has important physiological roles. Emerging biophysical evidence suggests that AQPs may also facilitate gas (CO2) and cation transport. AQPs may be involved in cell signalling for volume regulation and controlling the subcellular localization of other proteins by forming macromolecular complexes. This review examines the evidence for these diverse functions of AQPs as well their physiological relevance. MAJOR CONCLUSIONS As well as being crucial for water homeostasis, AQPs are involved in physiologically important transport of molecules other than water, regulation of surface expression of other membrane proteins, cell adhesion, and signalling in cell volume regulation. GENERAL SIGNIFICANCE Elucidating the full range of functional roles of AQPs beyond the passive conduction of water will improve our understanding of mammalian physiology in health and disease. The functional variety of AQPs makes them an exciting drug target and could provide routes to a range of novel therapies.
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Affiliation(s)
- Philip Kitchen
- Molecular Organisation and Assembly in Cells Doctoral Training Centre, University of Warwick, Coventry CV4 7AL, UK
| | - Rebecca E Day
- Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK
| | - Mootaz M Salman
- Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK
| | - Matthew T Conner
- Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK
| | - Roslyn M Bill
- School of Life & Health Sciences and Aston Research Centre for Healthy Ageing, Aston University, Aston Triangle, Birmingham B4 7ET, UK
| | - Alex C Conner
- Institute of Clinical Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
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12
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Hejtmancik JF, Riazuddin SA, McGreal R, Liu W, Cvekl A, Shiels A. Lens Biology and Biochemistry. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 134:169-201. [PMID: 26310155 DOI: 10.1016/bs.pmbts.2015.04.007] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The primary function of the lens resides in its transparency and ability to focus light on the retina. These require both that the lens cells contain high concentrations of densely packed lens crystallins to maintain a refractive index constant over distances approximating the wavelength of the light to be transmitted, and a specific arrangement of anterior epithelial cells and arcuate fiber cells lacking organelles in the nucleus to avoid blocking transmission of light. Because cells in the lens nucleus have shed their organelles, lens crystallins have to last for the lifetime of the organism, and are specifically adapted to this function. The lens crystallins comprise two major families: the βγ-crystallins are among the most stable proteins known and the α-crystallins, which have a chaperone-like function. Other proteins and metabolic activities of the lens are primarily organized to protect the crystallins from damage over time and to maintain homeostasis of the lens cells. Membrane protein channels maintain osmotic and ionic balance across the lens, while the lens cytoskeleton provides for the specific shape of the lens cells, especially the fiber cells of the nucleus. Perhaps most importantly, a large part of the metabolic activity in the lens is directed toward maintaining a reduced state, which shelters the lens crystallins and other cellular components from damage from UV light and oxidative stress. Finally, the energy requirements of the lens are met largely by glycolysis and the pentose phosphate pathway, perhaps in response to the avascular nature of the lens. Together, all these systems cooperate to maintain lens transparency over time.
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Affiliation(s)
- J Fielding Hejtmancik
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - S Amer Riazuddin
- The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Rebecca McGreal
- Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Wei Liu
- Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Ales Cvekl
- Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Alan Shiels
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, USA.
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Sindhu Kumari S, Gupta N, Shiels A, FitzGerald PG, Menon AG, Mathias RT, Varadaraj K. Role of Aquaporin 0 in lens biomechanics. Biochem Biophys Res Commun 2015; 462:339-45. [PMID: 25960294 DOI: 10.1016/j.bbrc.2015.04.138] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2015] [Accepted: 04/29/2015] [Indexed: 12/17/2022]
Abstract
Maintenance of proper biomechanics of the eye lens is important for its structural integrity and for the process of accommodation to focus near and far objects. Several studies have shown that specialized cytoskeletal systems such as the beaded filament (BF) and spectrin-actin networks contribute to mammalian lens biomechanics; mutations or deletion in these proteins alters lens biomechanics. Aquaporin 0 (AQP0), which constitutes ∼45% of the total membrane proteins of lens fiber cells, has been shown to function as a water channel and a structural cell-to-cell adhesion (CTCA) protein. Our recent ex vivo study on AQP0 knockout (AQP0 KO) mouse lenses showed the CTCA function of AQP0 could be crucial for establishing the refractive index gradient. However, biomechanical studies on the role of AQP0 are lacking. The present investigation used wild type (WT), AQP5 KO (AQP5(-/-)), AQP0 KO (heterozygous KO: AQP0(+/-); homozygous KO: AQP0(-/-); all in C57BL/6J) and WT-FVB/N mouse lenses to learn more about the role of fiber cell AQPs in lens biomechanics. Electron microscopic images exhibited decreases in lens fiber cell compaction and increases in extracellular space due to deletion of even one allele of AQP0. Biomechanical assay revealed that loss of one or both alleles of AQP0 caused a significant reduction in the compressive load-bearing capacity of the lenses compared to WT lenses. Conversely, loss of AQP5 did not alter the lens load-bearing ability. Compressive load-bearing at the suture area of AQP0(+/-) lenses showed easy separation while WT lens suture remained intact. These data from KO mouse lenses in conjunction with previous studies on lens-specific BF proteins (CP49 and filensin) suggest that AQP0 and BF proteins could act co-operatively in establishing normal lens biomechanics. We hypothesize that AQP0, with its prolific expression at the fiber cell membrane, could provide anchorage for cytoskeletal structures like BFs and together they help to confer fiber cell shape, architecture and integrity. To our knowledge, this is the first report identifying the involvement of an aquaporin in lens biomechanics. Since accommodation is required in human lenses for proper focusing, alteration in the adhesion and/or water channel functions of AQP0 could contribute to presbyopia.
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Affiliation(s)
- S Sindhu Kumari
- Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA
| | - Neha Gupta
- Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA
| | - Alan Shiels
- Washington University School of Medicine, St. Louis, MO, USA
| | - Paul G FitzGerald
- Cell Biology and Human Anatomy, School of Medicine, University of California, Davis, CA, USA
| | - Anil G Menon
- University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - Richard T Mathias
- Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA; SUNY Eye Institute, NY, USA
| | - Kulandaiappan Varadaraj
- Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA; SUNY Eye Institute, NY, USA.
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Orsini F, Santacroce M, Cremona A, Gosvami NN, Lascialfari A, Hoogenboom BW. Atomic force microscopy on plasma membranes from Xenopus laevis oocytes containing human aquaporin 4. J Mol Recognit 2014; 27:669-75. [PMID: 25277091 DOI: 10.1002/jmr.2390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 04/28/2014] [Accepted: 05/08/2014] [Indexed: 11/05/2022]
Abstract
Atomic force microscopy (AFM) is a unique tool for imaging membrane proteins in near-native environment (embedded in a membrane and in buffer solution) at ~1 nm spatial resolution. It has been most successful on membrane proteins reconstituted in 2D crystals and on some specialized and densely packed native membranes. Here, we report on AFM imaging of purified plasma membranes from Xenopus laevis oocytes, a commonly used system for the heterologous expression of membrane proteins. Isoform M23 of human aquaporin 4 (AQP4-M23) was expressed in the X. laevis oocytes following their injection with AQP4-M23 cRNA. AQP4-M23 expression and incorporation in the plasma membrane were confirmed by the changes in oocyte volume in response to applied osmotic gradients. Oocyte plasma membranes were then purified by ultracentrifugation on a discontinuous sucrose gradient, and the presence of AQP4-M23 proteins in the purified membranes was established by Western blotting analysis. Compared with membranes without over-expressed AQP4-M23, the membranes from AQP4-M23 cRNA injected oocytes showed clusters of structures with lateral size of about 10 nm in the AFM topography images, with a tendency to a fourfold symmetry as may be expected for higher-order arrays of AQP4-M23. In addition, but only infrequently, AQP4-M23 tetramers could be resolved in 2D arrays on top of the plasma membrane, in good quantitative agreement with transmission electron microscopy analysis and the current model of AQP4. Our results show the potential and the difficulties of AFM studies on cloned membrane proteins in native eukaryotic membranes.
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Affiliation(s)
- Francesco Orsini
- Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133, Milano, Italy
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15
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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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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: 39] [Impact Index Per Article: 3.9] [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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17
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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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18
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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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19
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Maddala R, Skiba NP, Lalane R, Sherman DL, Brophy PJ, Rao PV. Periaxin is required for hexagonal geometry and membrane organization of mature lens fibers. Dev Biol 2011; 357:179-90. [PMID: 21745462 PMCID: PMC3164832 DOI: 10.1016/j.ydbio.2011.06.036] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 06/14/2011] [Accepted: 06/14/2011] [Indexed: 01/06/2023]
Abstract
Transparency of the ocular lens depends on symmetric packing and membrane organization of highly elongated hexagonal fiber cells. These cells possess an extensive, well-ordered cortical cytoskeleton to maintain cell shape and to anchor membrane components. Periaxin (Prx), a PDZ domain protein involved in myelin sheath stabilization, is also a component of adhaerens plaques in lens fiber cells. Here we show that Prx is expressed in lens fibers and exhibits maturation dependent redistribution, clustering discretely at the tricellular junctions in mature fiber cells. Prx exists in a macromolecular complex with proteins involved in membrane organization including ankyrin-B, spectrin, NrCAM, filensin, ezrin and desmoyokin. Importantly, Prx knockout mouse lenses were found to be softer and more easily deformed than normal lenses, revealing disruptions in fiber cell hexagonal packing, membrane skeleton and membrane stability. These observations suggest a key role for Prx in maturation, packing, and membrane organization of lens fiber cells. Hence, there may be functional parallels between the roles of Prx in membrane stabilization of the myelin sheath and the lens fiber cell.
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Affiliation(s)
- Rupalatha Maddala
- Department of Ophthalmology, Duke University School of Medicine, NC. USA
| | - Nikolai P. Skiba
- Department of Ophthalmology, Duke University School of Medicine, NC. USA
| | - Robert Lalane
- Department of Ophthalmology, Duke University School of Medicine, NC. USA
| | - Diane L. Sherman
- Centre for Neuroregeneration, University of Edinburgh, Edinburgh, UK
| | - Peter J. Brophy
- Centre for Neuroregeneration, University of Edinburgh, Edinburgh, UK
| | - Ponugoti V. Rao
- Department of Ophthalmology, Duke University School of Medicine, NC. USA
- Department of Pharmacology and Cancer Biology, Duke University School of Medicine, NC. USA
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Ishibashi K, Kondo S, Hara S, Morishita Y. The evolutionary aspects of aquaporin family. Am J Physiol Regul Integr Comp Physiol 2011; 300:R566-76. [DOI: 10.1152/ajpregu.90464.2008] [Citation(s) in RCA: 135] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Aquaporins (AQPs) were originally identified as channels facilitating water transport across the plasma membrane. They have a pair of highly conserved signature sequences, asparagine-proline-alanine (NPA) boxes, to form a pore. However, some have little conserved amino acid sequences around the NPA boxes unclassifiable to two previous AQP subfamilies, classical AQPs and aquaglyceroporins. These will be called unorthodox AQPs in this review. Interestingly, these unorthodox AQPs have a highly conserved cysteine residue downstream of the second NPA box. AQPs also have a diversity of functions: some related to water transport such as fluid secretion, fluid absorption, and cell volume regulation, and the others not directly related to water transport such as cell adhesion, cell migration, cell proliferation, and cell differentiation. Some AQPs even permeate nonionic small molecules, ions, metals, and possibly gasses. AQP gene disruption studies have revealed their physiological roles: water transport in the kidney and exocrine glands, glycerol transport in fat metabolism and in skin moisture, and nutrient uptakes in plants. Furthermore, AQPs are also present at intracellular organelles, including tonoplasts, mitochondria, and the endoplasmic reticulum. This review focuses on the evolutionary aspects of AQPs from bacteria to humans in view of the structural and functional diversities of AQPs.
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Affiliation(s)
- Kenichi Ishibashi
- Department of Medical Physiology, Meiji Pharmaceutical University, Kiyose, Tokyo; and
| | - Shintaro Kondo
- Department of Medical Physiology, Meiji Pharmaceutical University, Kiyose, Tokyo; and
| | - Shigeki Hara
- Department of Medical Physiology, Meiji Pharmaceutical University, Kiyose, Tokyo; and
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Müller SA, Müller DJ, Engel A. Assessing the structure and function of single biomolecules with scanning transmission electron and atomic force microscopes. Micron 2011; 42:186-95. [DOI: 10.1016/j.micron.2010.10.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Revised: 10/05/2010] [Accepted: 10/05/2010] [Indexed: 11/30/2022]
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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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Plant Aquaporins: Roles in Water Homeostasis, Nutrition, and Signaling Processes. SIGNALING AND COMMUNICATION IN PLANTS 2011. [DOI: 10.1007/978-3-642-14369-4_1] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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24
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Liu LN, Sturgis JN, Scheuring S. Native architecture of the photosynthetic membrane from Rhodobacter veldkampii. J Struct Biol 2010; 173:138-45. [PMID: 20797440 DOI: 10.1016/j.jsb.2010.08.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Revised: 08/18/2010] [Accepted: 08/19/2010] [Indexed: 11/27/2022]
Abstract
The photosynthetic membrane in purple bacteria contains several pigment-protein complexes that assure light capture and establishment of the chemiosmotic gradient. The bioenergetic tasks of the photosynthetic membrane require the strong interaction between these various complexes. In the present work, we acquired the first images of the native outer membrane architecture and the supramolecular organization of the photosynthetic apparatus in vesicular chromatophores of Rhodobacter (Rb.) veldkampii. Mixed with LH2 (light-harvesting complex 2) rings, the PufX-containing LH1-RC (light-harvesting complex 1--reaction center) core complexes appear as C-shaped monomers, with random orientations in the photosynthetic membrane. Within the LH1 fence surrounding the RC, a remarkable gap that is probably occupied (or partially occupied) by PufX is visualized. Sequence alignment revealed that one specific region in PufX may be essential for PufX-induced core dimerization. In this region of ten amino acids in length all Rhodobacter species had five conserved amino acids, with the exception of Rb. veldkampii. Our findings provide direct evidence that the presence of PufX in Rb. veldkampii does not directly govern the dimerization of LH1-RC core complexes in the native membrane. It is indicated, furthermore, that the high membrane curvature of Rb. veldkampii chromatophores (Rb. veldkampii features equally small vesicular chromatophores alike Rb. sphaeroides) is not due to membrane bending induced by dimeric RC-LH1-PufX cores, as it has been proposed in Rb. sphaeroides.
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Affiliation(s)
- Lu-Ning Liu
- Institut Curie, U1006 INSERM, UMR168 CNRS, 26 Rue d'Ulm, 75248 Paris, France
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25
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El Kirat K, Morandat S, Dufrêne YF. Nanoscale analysis of supported lipid bilayers using atomic force microscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:750-65. [DOI: 10.1016/j.bbamem.2009.07.026] [Citation(s) in RCA: 120] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Revised: 07/17/2009] [Accepted: 07/23/2009] [Indexed: 12/11/2022]
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26
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Casuso I, Kodera N, Le Grimellec C, Ando T, Scheuring S. Contact-mode high-resolution high-speed atomic force microscopy movies of the purple membrane. Biophys J 2009; 97:1354-61. [PMID: 19720023 DOI: 10.1016/j.bpj.2009.06.019] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Revised: 06/08/2009] [Accepted: 06/15/2009] [Indexed: 11/16/2022] Open
Abstract
High-speed atomic force microscopy (HS-AFM) is becoming a reference tool for the study of dynamic biological processes. The spatial and time resolutions of HS-AFM are on the order of nanometers and milliseconds, respectively, and allow structural and functional characterization of biological processes at the single-molecule level. In this work we present contact-mode HS-AFM movies of purple membranes containing two-dimensional arrays of bacteriorhodopsin (bR). In high-resolution movies acquired at a 100 ms frame acquisition time, the substructure on individual bR trimers was visualized. In regions in between different bR arrays, dynamic topographies were observed and interpreted as motion of the bR trimers. Similarly, motion of bR monomers in the vicinity of lattice defects in the purple membrane was observed. Our findings indicate that the bR arrays are in a mobile association-dissociation equilibrium. HS-AFM on membranes provides novel perspectives for analyzing the membrane diffusion processes of nonlabeled molecules.
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Affiliation(s)
- Ignacio Casuso
- Institut Curie, Equipe Institut National de la Sante et de la Recherche Médicale Avenir, Unite Mixte de Recherche 168-Centre National de la Recherche Scientifique, Paris, France
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27
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Ziebarth NM, Rico F, Moy VT. Structural and Mechanical Mechanisms of Ocular Tissues Probed by AFM. ACTA ACUST UNITED AC 2009. [DOI: 10.1007/978-3-642-03535-7_11] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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28
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Liu LN, Duquesne K, Sturgis JN, Scheuring S. Quinone pathways in entire photosynthetic chromatophores of Rhodospirillum photometricum. J Mol Biol 2009; 393:27-35. [PMID: 19631224 DOI: 10.1016/j.jmb.2009.07.044] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2009] [Revised: 07/13/2009] [Accepted: 07/15/2009] [Indexed: 11/17/2022]
Abstract
In photosynthetic organisms, membrane pigment-protein complexes [light-harvesting complex 1 (LH1) and light-harvesting complex 2 (LH2)] harvest solar energy and convert sunlight into an electrical and redox potential gradient (reaction center) with high efficiency. Recent atomic force microscopy studies have described their organization in native membranes. However, the cytochrome (cyt) bc(1) complex remains unseen, and the important question of how reduction energy can efficiently pass from core complexes (reaction center and LH1) to distant cyt bc(1) via membrane-soluble quinones needs to be addressed. Here, we report atomic force microscopy images of entire chromatophores of Rhodospirillum photometricum. We found that core complexes influence their molecular environment within a critical radius of approximately 250 A. Due to the size mismatch with LH2, lipid membrane spaces favorable for quinone diffusion are found within this critical radius around cores. We show that core complexes form a network throughout entire chromatophores, providing potential quinone diffusion pathways that will considerably speed the redox energy transfer to distant cyt bc(1). These long-range quinone pathway networks result from cooperative short-range interactions of cores with their immediate environment.
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Affiliation(s)
- Lu-Ning Liu
- Institut Curie, Equipe INSERM Avenir, UMR168-CNRS, 26 Rue d'Ulm, 75248 Paris Cedex 05, France
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29
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Raunser S, Walz T. Electron crystallography as a technique to study the structure on membrane proteins in a lipidic environment. Annu Rev Biophys 2009; 38:89-105. [PMID: 19416061 DOI: 10.1146/annurev.biophys.050708.133649] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The native environment of integral membrane proteins is a lipid bilayer. The structure of a membrane protein is thus ideally studied in a lipidic environment. In the first part of this review we describe some membrane protein structures that revealed the surrounding lipids and provide a brief overview of the techniques that can be used to study membrane proteins in a lipidic environment. In the second part of this review we focus on electron crystallography of two-dimensional crystals as potentially the most suitable technique for such studies. We describe the individual steps involved in the electron crystallographic determination of a membrane protein structure and discuss current challenges that need to be overcome to transform electron crystallography into a technique that can be routinely used to analyze the structure of membrane proteins embedded in a lipid bilayer.
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Affiliation(s)
- Stefan Raunser
- Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany.
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30
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Fechner P, Boudier T, Mangenot S, Jaroslawski S, Sturgis JN, Scheuring S. Structural information, resolution, and noise in high-resolution atomic force microscopy topographs. Biophys J 2009; 96:3822-31. [PMID: 19413988 PMCID: PMC2711429 DOI: 10.1016/j.bpj.2009.02.011] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Revised: 12/10/2008] [Accepted: 02/04/2009] [Indexed: 11/22/2022] Open
Abstract
AFM has developed into a powerful tool in structural biology, providing topographs of proteins under close-to-native conditions and featuring an outstanding signal/noise ratio. However, the imaging mechanism exhibits particularities: fast and slow scan axis represent two independent image acquisition axes. Additionally, unknown tip geometry and tip-sample interaction render the contrast transfer function nondefinable. Hence, the interpretation of AFM topographs remained difficult. How can noise and distortions present in AFM images be quantified? How does the number of molecule topographs merged influence the structural information provided by averages? What is the resolution of topographs? Here, we find that in high-resolution AFM topographs, many molecule images are only slightly disturbed by noise, distortions, and tip-sample interactions. To identify these high-quality particles, we propose a selection criterion based on the internal symmetry of the imaged protein. We introduce a novel feature-based resolution analysis and show that AFM topographs of different proteins contain structural information beginning at different resolution thresholds: 10 A (AqpZ), 12 A (AQP0), 13 A (AQP2), and 20 A (light-harvesting-complex-2). Importantly, we highlight that the best single-molecule images are more accurate molecular representations than ensemble averages, because averaging downsizes the z-dimension and "blurs" structural details.
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Key Words
- 2d, two-dimensional
- 3d, three-dimensional
- acv, auto-correlation value
- afm, atomic force microscopy
- aqp0, aquaporin-0
- aqp2, aquaporin-2
- aqpz, aquaporin-z
- br, bacteriorhodopsin
- ccv, cross-correlation value
- ctf, contrast transfer function
- dpr, differential phase residual
- em, electron microscopy
- frc, fourier ring correlation
- fsc, fourier shell correlation
- is, internal symmetry
- lh2, light-harvesting-complex 2
- rmsd, root mean-square deviation
- sd, standard deviation
- snr, signal/noise ratio
- ssnr, spectral signal/noise ratio
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Affiliation(s)
- Peter Fechner
- Institut Curie, Équipe Institut National de la Santé et de la Recherche Médicale Avenir, 75248 Paris, France
| | - Thomas Boudier
- Institut de Biologie Intégrative, Institut Fédératif de Recherche 83, Université Pierre et Marie Curie, Paris, France
| | - Stéphanie Mangenot
- Institut Curie, Équipe Institut National de la Santé et de la Recherche Médicale Avenir, 75248 Paris, France
- Université Paris-Sud, 91405 Orsay, France
| | - Szymon Jaroslawski
- Institut Curie, Équipe Institut National de la Santé et de la Recherche Médicale Avenir, 75248 Paris, France
| | - James N. Sturgis
- UPR-9027 Laboratoire d'Ingénierie des Systèmes Macromoléculaires, Institut de Microbiologie de la Méditerranée, Centre National de la Recherche Scientifique–Aix-Marseille Université, 13402 Marseille, France
| | - Simon Scheuring
- Institut Curie, Équipe Institut National de la Santé et de la Recherche Médicale Avenir, 75248 Paris, France
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Atomic force microscopy of biological membranes. Biophys J 2009; 96:329-38. [PMID: 19167286 DOI: 10.1016/j.bpj.2008.09.046] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2008] [Accepted: 09/15/2008] [Indexed: 11/21/2022] Open
Abstract
Atomic force microscopy (AFM) is an ideal method to study the surface topography of biological membranes. It allows membranes that are adsorbed to flat solid supports to be raster-scanned in physiological solutions with an atomically sharp tip. Therefore, AFM is capable of observing biological molecular machines at work. In addition, the tip can be tethered to the end of a single membrane protein, and forces acting on the tip upon its retraction indicate barriers that occur during the process of protein unfolding. Here we discuss the fundamental limitations of AFM determined by the properties of cantilevers, present aspects of sample preparation, and review results achieved on reconstituted and native biological membranes.
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Chepelinsky AB. Structural function of MIP/aquaporin 0 in the eye lens; genetic defects lead to congenital inherited cataracts. Handb Exp Pharmacol 2008:265-97. [PMID: 19096783 DOI: 10.1007/978-3-540-79885-9_14] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Aquaporin 0 (AQP0) was originally characterized as a membrane intrinsic protein, specifically expressed in the lens fibers of the ocular lens and designated MIP, for major intrinsic protein of the lens. Once the gene was cloned, an internal repeat was identified, encoding for the amino acids Asp-Pro-Ala, the NPA repeat. Shortly, the MIP gene family was emerging, with members being characterized in mammals, insects, and plants. Once Peter Agre's laboratory developed a functional assay for water channels, the MIP family became the aquaporin family and MIP became known as aquaporin 0. Besides functioning as a water channel, aquaporin 0 also plays a structural role, being required for maintaining the transparency and optical accommodation of the ocular lens. Mutations in the AQP0 gene in human and mice result in genetic cataracts; deletion of the MIP/AQP0 gene in mice results in lack of suture formation required for maintenance of the lens fiber architecture, resulting in perturbed accommodation and focus properties of the ocular lens. Crystallography studies support the notion of the double function of aquaporin 0 as a water channel (open configuration) or adhesion molecule (closed configuration) in the ocular lens fibers. The functions of MIP/AQP0, both as a water channel and an adhesive molecule in the lens fibers, contribute to the narrow intercellular space of the lens fibers that is required for lens transparency and accommodation.
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Affiliation(s)
- Ana B Chepelinsky
- National Institutes of Health, National Eye Institute, Bldg. 31, Room 6A-32, Bethesda, MD, 20892-2510, USA.
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Mangenot S, Buzhynskyy N, Girmens JF, Scheuring S. Malformation of junctional microdomains in cataract lens membranes from a type II diabetes patient. Pflugers Arch 2008; 457:1265-74. [PMID: 19034495 DOI: 10.1007/s00424-008-0604-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2008] [Revised: 10/04/2008] [Accepted: 10/15/2008] [Indexed: 11/30/2022]
Abstract
In eye core lens membranes, aquaporin-0 (AQP0) and connexins (Cx) form together well-structured supramolecular assemblies, the junctional microdomains, in which they assure water, ion, metabolite, and waste transport. Additionally, they mediate cell-cell adhesion-forming thin junctions (AQP0) and gap junctions (Cx). We have used atomic force microscopy and biochemical methods to analyze and compare the structure of junctional microdomains in human cataract lens membranes from a type II diabetes patient and healthy lens membranes from calf. A healthy intercellular junctional microdomain consists in average of approximately 150 tetragonally arranged (a = b = 65.5 A, gamma = 90 degrees) AQP0 tetramers surrounded by densely packed non-ordered connexon channels. Gap-junction connexons act as lineactants inside the membrane and confine AQP0 in the junctional microdomains. In the diabetic cataract lens, connexons were degraded, and AQP0 arrays are malformed. We conceptualize that absence of connexons lead to breakdown of cell nutrition.
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Affiliation(s)
- Stéphanie Mangenot
- Institut Curie, Equipe INSERM Avenir, UMR168-CNRS, 26 Rue d'Ulm, 75248 Paris Cedex 05, France
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Affiliation(s)
- Andreas Engel
- Maurice E. Müller Institute for Structural Biology, Biozentrum, University of Basel, 4056 Basel, Switzerland;
| | - Hermann E. Gaub
- Center for Nanoscience and Physics Department, University Munich, 80799 Munich, Germany;
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Suzuki H, Nishikawa K, Hiroaki Y, Fujiyoshi Y. Formation of aquaporin-4 arrays is inhibited by palmitoylation of N-terminal cysteine residues. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1181-9. [DOI: 10.1016/j.bbamem.2007.12.007] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Revised: 12/09/2007] [Accepted: 12/11/2007] [Indexed: 11/25/2022]
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Sorbo JG, Moe SE, Ottersen OP, Holen T. The molecular composition of square arrays. Biochemistry 2008; 47:2631-7. [PMID: 18247481 DOI: 10.1021/bi702146k] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Square arrays are prominent structures in plasma membranes of brain, muscle, and kidneys with an unknown function. So far, the analysis of these arrays has been restricted to freeze fracture preparations, which have shown square arrays to contain the water channel Aquaporin-4 (AQP4). Using Blue-Native PAGE immunoblots, we provide evidence that higher-order AQP4 complexes correspond to square arrays, with the AQP4 isoform M23 playing a dominant role. Our data are consistent with the idea that square arrays consist of aggregates of AQP4 tetramers complexed with multiples of dimers. By comparison, Aquaporin-1 and Aquaporin-9 form tetramers, but not higher-order complexes. AQP4 square arrays are stable under several biochemical purification steps. Analyzing the internal composition of the higher-order complexes by 2D gels, we demonstrate that the square arrays in addition to M23 also invariably contain AQP4, M1, and a novel AQP4 isoform that we call Mz. The visualization AQP4 square arrays by a rapid, biochemical assay provides new insight in the molecular organization of square arrays and gives further proof of the heterogeneity of AQP4 square arrays in vivo.
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Affiliation(s)
- Jan Gunnar Sorbo
- Center for Molecular Biology and Neuroscience (CMBN), and Nordic Center of Excellence for Research in Water Imbalance Related Disorders (WIRED), University of Oslo, Oslo 0317, Norway
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37
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Buzhynskyy N, Girmens JF, Faigle W, Scheuring S. Human Cataract Lens Membrane at Subnanometer Resolution. J Mol Biol 2007; 374:162-9. [DOI: 10.1016/j.jmb.2007.09.022] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2007] [Revised: 08/31/2007] [Accepted: 09/06/2007] [Indexed: 10/22/2022]
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