2008 |
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Andrews, Simeon ; Reichow, Steve L; Gonen, Tamir Electron Crystallography of Aquaporins Journal Article IUBMB Life, 60 (7), pp. 430–436, 2008. @article{pmid18465794, title = {Electron Crystallography of Aquaporins}, author = {Andrews, Simeon and Reichow, Steve L. and Gonen, Tamir}, url = {https://cryoem.ucla.edu/wp-content/uploads/andrews_2008.pdf, Main text}, doi = {10.1002/iub.53}, year = {2008}, date = {2008-05-08}, journal = {IUBMB Life}, volume = {60}, number = {7}, pages = {430--436}, abstract = {Aquaporins are a family of ubiquitous membrane proteins that form a pore for the permeation of water. Both electron and X-ray crystallography played major roles in determining the atomic structures of a number of aquaporins. This review focuses on electron crystallography, and its contribution to the field of aquaporin biology. We briefly discuss electron crystallography and the two-dimensional crystallization process. We describe features of aquaporins common to both electron and X-ray crystallographic structures; as well as some structural insights unique to electron crystallography, including aquaporin junction formation and lipid-protein interactions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Aquaporins are a family of ubiquitous membrane proteins that form a pore for the permeation of water. Both electron and X-ray crystallography played major roles in determining the atomic structures of a number of aquaporins. This review focuses on electron crystallography, and its contribution to the field of aquaporin biology. We briefly discuss electron crystallography and the two-dimensional crystallization process. We describe features of aquaporins common to both electron and X-ray crystallographic structures; as well as some structural insights unique to electron crystallography, including aquaporin junction formation and lipid-protein interactions. | |
Engel, Andreas; Fujiyoshi, Yoshinori; Gonen, Tamir; Walz, Thomas Junction-forming aquaporins Journal Article Curr. Opin. Struct. Biol., 18 (2), pp. 229–235, 2008. @article{pmid18194855, title = {Junction-forming aquaporins}, author = {Andreas Engel and Yoshinori Fujiyoshi and Tamir Gonen and Thomas Walz}, url = {https://cryoem.ucla.edu/wp-content/uploads/engel_2008.pdf, Main text}, doi = {10.1016/j.sbi.2007.11.003}, year = {2008}, date = {2008-04-01}, journal = {Curr. Opin. Struct. Biol.}, volume = {18}, number = {2}, pages = {229--235}, abstract = {Aquaporins (AQPs) are a family of ubiquitous membrane channels that conduct water and solutes across membranes. This review focuses on AQP0 and AQP4, which in addition to forming water channels also appear to play a role in cell adhesion. We discuss the recently determined structures of the membrane junctions mediated by these two AQPs, the mechanisms that regulate junction formation, and evidence that supports a role for AQP0 and AQP4 in cell adhesion.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Aquaporins (AQPs) are a family of ubiquitous membrane channels that conduct water and solutes across membranes. This review focuses on AQP0 and AQP4, which in addition to forming water channels also appear to play a role in cell adhesion. We discuss the recently determined structures of the membrane junctions mediated by these two AQPs, the mechanisms that regulate junction formation, and evidence that supports a role for AQP0 and AQP4 in cell adhesion. | |
Zheng, Hongjin; Olia, Adam S; Gonen, Melissa; Andrews, Simeon; Cingolani, Gino; Gonen, Tamir A Conformational Switch in Bacteriophage P22 Portal Protein Primes Genome Injection Journal Article Mol. Cell, 29 (3), pp. 376–383, 2008. @article{pmid18280242, title = {A Conformational Switch in Bacteriophage P22 Portal Protein Primes Genome Injection}, author = {Hongjin Zheng and Adam S Olia and Melissa Gonen and Simeon Andrews and Gino Cingolani and Tamir Gonen}, url = {https://cryoem.ucla.edu/wp-content/uploads/zheng_2008.pdf, Main text}, doi = {10.1016/j.molcel.2007.11.034}, year = {2008}, date = {2008-02-15}, journal = {Mol. Cell}, volume = {29}, number = {3}, pages = {376--383}, abstract = {Double-stranded DNA (dsDNA) viruses such as herpesviruses and bacteriophages infect by delivering their genetic material into cells, a task mediated by a DNA channel called "portal protein." We have used electron cryomicroscopy to determine the structure of bacteriophage P22 portal protein in both the procapsid and mature capsid conformations. We find that, just as the viral capsid undergoes major conformational changes during virus maturation, the portal protein switches conformation from a procapsid to a mature phage state upon binding of gp4, the factor that initiates tail assembly. This dramatic conformational change traverses the entire length of the DNA channel, from the outside of the virus to the inner shell, and erects a large dome domain directly above the DNA channel that binds dsDNA inside the capsid. We hypothesize that this conformational change primes dsDNA for injection and directly couples completion of virus morphogenesis to a new cycle of infection.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Double-stranded DNA (dsDNA) viruses such as herpesviruses and bacteriophages infect by delivering their genetic material into cells, a task mediated by a DNA channel called "portal protein." We have used electron cryomicroscopy to determine the structure of bacteriophage P22 portal protein in both the procapsid and mature capsid conformations. We find that, just as the viral capsid undergoes major conformational changes during virus maturation, the portal protein switches conformation from a procapsid to a mature phage state upon binding of gp4, the factor that initiates tail assembly. This dramatic conformational change traverses the entire length of the DNA channel, from the outside of the virus to the inner shell, and erects a large dome domain directly above the DNA channel that binds dsDNA inside the capsid. We hypothesize that this conformational change primes dsDNA for injection and directly couples completion of virus morphogenesis to a new cycle of infection. | |
Gonen, Tamir; Hite, Richard K; Cheng, Yifan; Petre, Benjamin M; Kistler, Joerg; Walz, Thomas Polymorphic Assemblies and Crystalline Arrays of Lens Tetraspanin MP20 Journal Article J. Mol. Biol., 376 (2), pp. 380–392, 2008. @article{pmid18166196, title = {Polymorphic Assemblies and Crystalline Arrays of Lens Tetraspanin MP20}, author = {Tamir Gonen and Richard K Hite and Yifan Cheng and Benjamin M Petre and Joerg Kistler and Thomas Walz}, url = {https://cryoem.ucla.edu/wp-content/uploads/gonen_2008.pdf, Main text}, doi = {10.1016/j.jmb.2007.09.001}, year = {2008}, date = {2008-02-15}, journal = {J. Mol. Biol.}, volume = {376}, number = {2}, pages = {380--392}, abstract = {Members of the tetraspanin superfamily function as transmembrane scaffold proteins that mediate the assembly of membrane proteins into specific signaling complexes. Tetraspanins also interact with each other and concentrate membrane proteins into tetraspanin-enriched microdomains (TEMs). Here we report that lens-specific tetraspanin MP20 can form multiple types of higher-order assemblies and we present crystalline arrays of MP20. When isolated in the absence of divalent cations, MP20 is solubilized predominantly in tetrameric form, whereas the presence of divalent cations during solubilization promotes the association of MP20 tetramers into higher-order species. This effect only occurs when divalent cations are present during solubilization but not when divalent cations are added to solubilized tetrameric MP20, suggesting that other factors may also be involved. When purified MP20 tetramers are reconstituted with native lens lipids in the presence of magnesium, MP20 forms two-dimensional (2D) crystals. A projection map at 18 A resolution calculated from negatively stained 2D crystals showed that the building block of the crystal is an octamer consisting of two tetramers related to each other by 2-fold symmetry. In addition to 2D crystals, reconstitution of MP20 with native lipids also produced a variety of large protein-lipid complexes, and we present three-dimensional (3D) reconstructions of the four most abundant of these complexes in negative stain. The various complexes formed by MP20 most likely reflect the many ways in which tetraspanins can interact with each other to allow formation of TEMs.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Members of the tetraspanin superfamily function as transmembrane scaffold proteins that mediate the assembly of membrane proteins into specific signaling complexes. Tetraspanins also interact with each other and concentrate membrane proteins into tetraspanin-enriched microdomains (TEMs). Here we report that lens-specific tetraspanin MP20 can form multiple types of higher-order assemblies and we present crystalline arrays of MP20. When isolated in the absence of divalent cations, MP20 is solubilized predominantly in tetrameric form, whereas the presence of divalent cations during solubilization promotes the association of MP20 tetramers into higher-order species. This effect only occurs when divalent cations are present during solubilization but not when divalent cations are added to solubilized tetrameric MP20, suggesting that other factors may also be involved. When purified MP20 tetramers are reconstituted with native lens lipids in the presence of magnesium, MP20 forms two-dimensional (2D) crystals. A projection map at 18 A resolution calculated from negatively stained 2D crystals showed that the building block of the crystal is an octamer consisting of two tetramers related to each other by 2-fold symmetry. In addition to 2D crystals, reconstitution of MP20 with native lipids also produced a variety of large protein-lipid complexes, and we present three-dimensional (3D) reconstructions of the four most abundant of these complexes in negative stain. The various complexes formed by MP20 most likely reflect the many ways in which tetraspanins can interact with each other to allow formation of TEMs. | |
2007 |
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Franck, Andrew D; Powers, Andrew F; Gestaut, Daniel R; Gonen, Tamir; Davis, Trisha N; Asbury, Charles L Tension applied through the Dam1 complex promotes microtubule elongation providing a direct mechanism for length control in mitosis Journal Article Nat. Cell Biol., 9 (7), pp. 832–837, 2007. @article{pmid17572669, title = {Tension applied through the Dam1 complex promotes microtubule elongation providing a direct mechanism for length control in mitosis}, author = {Andrew D Franck and Andrew F Powers and Daniel R Gestaut and Tamir Gonen and Trisha N Davis and Charles L Asbury}, url = {https://cryoem.ucla.edu/wp-content/uploads/franck2007.pdf, Main text}, doi = {10.1038/ncb1609}, year = {2007}, date = {2007-06-17}, journal = {Nat. Cell Biol.}, volume = {9}, number = {7}, pages = {832--837}, abstract = {In dividing cells, kinetochores couple chromosomes to the tips of growing and shortening microtubule fibres and tension at the kinetochore-microtubule interface promotes fibre elongation. Tension-dependent microtubule fibre elongation is thought to be essential for coordinating chromosome alignment and separation, but the mechanism underlying this effect is unknown. Using optical tweezers, we applied tension to a model of the kinetochore-microtubule interface composed of the yeast Dam1 complex bound to individual dynamic microtubule tips. Higher tension decreased the likelihood that growing tips would begin to shorten, slowed shortening, and increased the likelihood that shortening tips would resume growth. These effects are similar to the effects of tension on kinetochore-attached microtubule fibres in many cell types, suggesting that we have reconstituted a direct mechanism for microtubule-length control in mitosis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In dividing cells, kinetochores couple chromosomes to the tips of growing and shortening microtubule fibres and tension at the kinetochore-microtubule interface promotes fibre elongation. Tension-dependent microtubule fibre elongation is thought to be essential for coordinating chromosome alignment and separation, but the mechanism underlying this effect is unknown. Using optical tweezers, we applied tension to a model of the kinetochore-microtubule interface composed of the yeast Dam1 complex bound to individual dynamic microtubule tips. Higher tension decreased the likelihood that growing tips would begin to shorten, slowed shortening, and increased the likelihood that shortening tips would resume growth. These effects are similar to the effects of tension on kinetochore-attached microtubule fibres in many cell types, suggesting that we have reconstituted a direct mechanism for microtubule-length control in mitosis. | |
Viadiu, Hector; Gonen, Tamir; Walz, Thomas Projection Map of Aquaporin-9 at 7 Å Resolution Journal Article J. Mol. Biol., 367 (1), pp. 80–88, 2007. @article{pmid17239399, title = {Projection Map of Aquaporin-9 at 7 Å Resolution}, author = {Hector Viadiu and Tamir Gonen and Thomas Walz}, url = {https://cryoem.ucla.edu/wp-content/uploads/Viadiu_2006.pdf, Main text}, doi = {10.1016/j.jmb.2006.12.042}, year = {2007}, date = {2007-03-16}, journal = {J. Mol. Biol.}, volume = {367}, number = {1}, pages = {80--88}, abstract = {Aquaporin-9, an aquaglyceroporin present in diverse tissues, is unique among aquaporins because it is not only permeable to water, urea and glycerol, but also allows passage of larger uncharged solutes. Single particle analysis of negatively stained recombinant rat aquaporin-9 revealed a particle size characteristic of the tetrameric organization of all members of the aquaporin family. Reconstitution of aquaporin-9 into two-dimensional crystals enabled us to calculate a projection map at 7 A resolution. The projection structure indicates a tetrameric structure, similar to GlpF, with each square-like monomer forming a pore. A comparison of the pore-lining residues between the crystal structure of GlpF and a homology model of aquaporin-9 locates substitutions in these residues predominantly to the hydrophobic edge of the tripathic pore of GlpF, providing first insights into the structural basis for the broader substrate specificity of aquaporin-9.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Aquaporin-9, an aquaglyceroporin present in diverse tissues, is unique among aquaporins because it is not only permeable to water, urea and glycerol, but also allows passage of larger uncharged solutes. Single particle analysis of negatively stained recombinant rat aquaporin-9 revealed a particle size characteristic of the tetrameric organization of all members of the aquaporin family. Reconstitution of aquaporin-9 into two-dimensional crystals enabled us to calculate a projection map at 7 A resolution. The projection structure indicates a tetrameric structure, similar to GlpF, with each square-like monomer forming a pore. A comparison of the pore-lining residues between the crystal structure of GlpF and a homology model of aquaporin-9 locates substitutions in these residues predominantly to the hydrophobic edge of the tripathic pore of GlpF, providing first insights into the structural basis for the broader substrate specificity of aquaporin-9. | |
2006 |
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Gonen, Tamir; Walz, Thomas The structure of aquaporins Journal Article Q. Rev. Biophys., 39 (4), pp. 361–396, 2006. @article{pmid17156589, title = {The structure of aquaporins}, author = {Tamir Gonen and Thomas Walz}, url = {https://cryoem.ucla.edu/wp-content/uploads/gonenwalz_2006.pdf, Main text}, doi = {10.1017/S0033583506004458}, year = {2006}, date = {2006-11-01}, journal = {Q. Rev. Biophys.}, volume = {39}, number = {4}, pages = {361--396}, abstract = {The ubiquitous members of the aquaporin (AQP) family form transmembrane pores that are either exclusive for water (aquaporins) or are also permeable for other small neutral solutes such as glycerol (aquaglyceroporins). The purpose of this review is to provide an overview of our current knowledge of AQP structures and to describe the structural features that define the function of these membrane pores. The review will discuss the mechanisms governing water conduction, proton exclusion and substrate specificity, and how the pore permeability is regulated in different members of the AQP family.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The ubiquitous members of the aquaporin (AQP) family form transmembrane pores that are either exclusive for water (aquaporins) or are also permeable for other small neutral solutes such as glycerol (aquaglyceroporins). The purpose of this review is to provide an overview of our current knowledge of AQP structures and to describe the structural features that define the function of these membrane pores. The review will discuss the mechanisms governing water conduction, proton exclusion and substrate specificity, and how the pore permeability is regulated in different members of the AQP family. | |
2005 |
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Gonen, Tamir; Cheng, Yifan; Sliz, Piotr; Hiroaki, Yoko; Fujiyoshi, Yoshinori; Harrison, Stephen C; Walz, Thomas Lipid-protein interactions in double-layered two-dimensional AQP0 crystals Journal Article Nature, 438 (7068), pp. 633–638, 2005. @article{pmid16319884, title = {Lipid-protein interactions in double-layered two-dimensional AQP0 crystals}, author = {Tamir Gonen and Yifan Cheng and Piotr Sliz and Yoko Hiroaki and Yoshinori Fujiyoshi and Stephen C Harrison and Thomas Walz}, url = {https://cryoem.ucla.edu/wp-content/uploads/Gonen_2005.pdf, Main text}, doi = {10.1038/nature04321}, year = {2005}, date = {2005-12-01}, journal = {Nature}, volume = {438}, number = {7068}, pages = {633--638}, abstract = {Lens-specific aquaporin-0 (AQP0) functions as a specific water pore and forms the thin junctions between fibre cells. Here we describe a 1.9 A resolution structure of junctional AQP0, determined by electron crystallography of double-layered two-dimensional crystals. Comparison of junctional and non-junctional AQP0 structures shows that junction formation depends on a conformational switch in an extracellular loop, which may result from cleavage of the cytoplasmic amino and carboxy termini. In the centre of the water pathway, the closed pore in junctional AQP0 retains only three water molecules, which are too widely spaced to form hydrogen bonds with each other. Packing interactions between AQP0 tetramers in the crystalline array are mediated by lipid molecules, which assume preferred conformations. We were therefore able to build an atomic model for the lipid bilayer surrounding the AQP0 tetramers, and we describe lipid-protein interactions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Lens-specific aquaporin-0 (AQP0) functions as a specific water pore and forms the thin junctions between fibre cells. Here we describe a 1.9 A resolution structure of junctional AQP0, determined by electron crystallography of double-layered two-dimensional crystals. Comparison of junctional and non-junctional AQP0 structures shows that junction formation depends on a conformational switch in an extracellular loop, which may result from cleavage of the cytoplasmic amino and carboxy termini. In the centre of the water pathway, the closed pore in junctional AQP0 retains only three water molecules, which are too widely spaced to form hydrogen bonds with each other. Packing interactions between AQP0 tetramers in the crystalline array are mediated by lipid molecules, which assume preferred conformations. We were therefore able to build an atomic model for the lipid bilayer surrounding the AQP0 tetramers, and we describe lipid-protein interactions. | |
2004 |
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Gonen, Tamir; Cheng, Yifan; Kistler, Joerg; Walz, Thomas Aquaporin-0 Membrane Junctions Form Upon Proteolytic Cleavage Journal Article J. Mol. Biol., 342 (4), pp. 1337–1345, 2004. @article{pmid15351655, title = {Aquaporin-0 Membrane Junctions Form Upon Proteolytic Cleavage}, author = {Tamir Gonen and Yifan Cheng and Joerg Kistler and Thomas Walz}, url = {https://cryoem.ucla.edu/wp-content/uploads/Gonen_2004b.pdf, Main text}, doi = {10.1016/j.jmb.2004.07.076}, year = {2004}, date = {2004-09-24}, journal = {J. Mol. Biol.}, volume = {342}, number = {4}, pages = {1337--1345}, abstract = {Aquaporin-0 (AQP0), previously known as major intrinsic protein (MIP), is the only water pore protein expressed in lens fiber cells. AQP0 is highly specific to lens fiber cells and constitutes the most abundant intrinsic membrane protein in these cells. The protein is initially expressed as a full-length protein in young fiber cells in the lens cortex, but becomes increasingly cleaved in the lens core region. Reconstitution of AQP0 isolated from the core of sheep lenses containing a proportion of truncated protein, produced double-layered two-dimensional (2D) crystals, which displayed the same dimensions as the thin 11 nm lens fiber cell junctions, which are prominent in the lens core. In contrast reconstitution of full-length AQP0 isolated from the lens cortex reproducibly yielded single-layered 2D crystals. We present electron diffraction patterns and projection maps of both crystal types. We show that cleavage of the intracellular C terminus enhances the adhesive properties of the extracellular surface of AQP0, indicating a conformational change in the molecule. This change of function of AQP0 from a water pore in the cortex to an adhesion molecule in the lens core constitutes another manifestation of the gene sharing concept originally proposed on the basis of the dual function of crystallins.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Aquaporin-0 (AQP0), previously known as major intrinsic protein (MIP), is the only water pore protein expressed in lens fiber cells. AQP0 is highly specific to lens fiber cells and constitutes the most abundant intrinsic membrane protein in these cells. The protein is initially expressed as a full-length protein in young fiber cells in the lens cortex, but becomes increasingly cleaved in the lens core region. Reconstitution of AQP0 isolated from the core of sheep lenses containing a proportion of truncated protein, produced double-layered two-dimensional (2D) crystals, which displayed the same dimensions as the thin 11 nm lens fiber cell junctions, which are prominent in the lens core. In contrast reconstitution of full-length AQP0 isolated from the lens cortex reproducibly yielded single-layered 2D crystals. We present electron diffraction patterns and projection maps of both crystal types. We show that cleavage of the intracellular C terminus enhances the adhesive properties of the extracellular surface of AQP0, indicating a conformational change in the molecule. This change of function of AQP0 from a water pore in the cortex to an adhesion molecule in the lens core constitutes another manifestation of the gene sharing concept originally proposed on the basis of the dual function of crystallins. | |
Gonen, Tamir; Sliz, Piotr; Kistler, Joerg; Cheng, Yifan; Walz, Thomas Aquaporin-0 membrane junctions reveal the structure of a closed water pore Journal Article Nature, 429 (6988), pp. 193–197, 2004. @article{pmid15141214, title = {Aquaporin-0 membrane junctions reveal the structure of a closed water pore}, author = {Tamir Gonen and Piotr Sliz and Joerg Kistler and Yifan Cheng and Thomas Walz}, url = {https://cryoem.ucla.edu/wp-content/uploads/gonen_2004a.pdf, Main text}, doi = {10.1038/nature02503}, year = {2004}, date = {2004-05-13}, journal = {Nature}, volume = {429}, number = {6988}, pages = {193--197}, abstract = {The lens-specific water pore aquaporin-0 (AQP0) is the only aquaporin known to form membrane junctions in vivo. We show here that AQP0 from the lens core, containing some carboxy-terminally cleaved AQP0, forms double-layered crystals that recapitulate in vivo junctions. We present the structure of the AQP0 membrane junction as determined by electron crystallography. The junction is formed by three localized interactions between AQP0 molecules in adjoining membranes, mainly mediated by proline residues conserved in AQP0s from different species but not present in most other aquaporins. Whereas all previously determined aquaporin structures show the pore in an open conformation, the water pore is closed in AQP0 junctions. The water pathway in AQP0 also contains an additional pore constriction, not seen in other known aquaporin structures, which may be responsible for pore gating.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The lens-specific water pore aquaporin-0 (AQP0) is the only aquaporin known to form membrane junctions in vivo. We show here that AQP0 from the lens core, containing some carboxy-terminally cleaved AQP0, forms double-layered crystals that recapitulate in vivo junctions. We present the structure of the AQP0 membrane junction as determined by electron crystallography. The junction is formed by three localized interactions between AQP0 molecules in adjoining membranes, mainly mediated by proline residues conserved in AQP0s from different species but not present in most other aquaporins. Whereas all previously determined aquaporin structures show the pore in an open conformation, the water pore is closed in AQP0 junctions. The water pathway in AQP0 also contains an additional pore constriction, not seen in other known aquaporin structures, which may be responsible for pore gating. | |
2003 |
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Grey, Angus C; Jacobs, Marc D; Gonen, Tamir; Kistler, Joerg; Donaldson, Paul J Insertion of MP20 into lens fibre cell plasma membranes correlates with the formation of an extracellular diffusion barrier Journal Article Exp. Eye Res., 77 (5), pp. 567–574, 2003. @article{pmid14550398, title = {Insertion of MP20 into lens fibre cell plasma membranes correlates with the formation of an extracellular diffusion barrier}, author = {Angus C Grey and Marc D Jacobs and Tamir Gonen and Joerg Kistler and Paul J Donaldson}, url = {https://cryoem.ucla.edu/wp-content/uploads/grey_2003.pdf, Main text}, doi = {10.1016/s0014-4835(03)00192-1}, year = {2003}, date = {2003-11-01}, journal = {Exp. Eye Res.}, volume = {77}, number = {5}, pages = {567--574}, abstract = {It is known that during lens differentiation a number of fibre cell specific membrane proteins change their expression profiles. In this study we have investigated how the profiles of the two most abundant fibre cell membrane proteins AQP0 (formerly known as Major Intrinsic Protein, MIP) and MP20 change as a function of fibre cell differentiation. While AQP0 was always found associated with fibre cell membranes, MP20 was initially found in the cytoplasm of peripheral fibre cells before becoming inserted into the membranes of deeper fibre cells. To determine at what stage in fibre cell differentiation MP20 becomes inserted into the membrane, sections were double-labelled with an antibody against MP20, and propidium iodide, a marker of cell nuclei. This showed that membrane insertion of MP20 occurs in a discrete transition zone that coincided with the degradation of cell nuclei. To test the significance of the membrane insertion of MP20 to overall lens function, whole lenses were incubated for varying times in a solution containing either Texas Red-dextran or Lucifer yellow as markers of extracellular space. Lenses were fixed and then processed for immunocytochemistry. Analysis of these sections showed that both tracer dyes were excluded from the extracellular space in an area that coincided with insertion of MP20 into the plasma membrane. Our results suggest that the insertion of MP20 into fibre cell membranes coincides with the creation of a barrier that restricts the diffusion of molecules into the lens core via the extracellular space.}, keywords = {}, pubstate = {published}, tppubtype = {article} } It is known that during lens differentiation a number of fibre cell specific membrane proteins change their expression profiles. In this study we have investigated how the profiles of the two most abundant fibre cell membrane proteins AQP0 (formerly known as Major Intrinsic Protein, MIP) and MP20 change as a function of fibre cell differentiation. While AQP0 was always found associated with fibre cell membranes, MP20 was initially found in the cytoplasm of peripheral fibre cells before becoming inserted into the membranes of deeper fibre cells. To determine at what stage in fibre cell differentiation MP20 becomes inserted into the membrane, sections were double-labelled with an antibody against MP20, and propidium iodide, a marker of cell nuclei. This showed that membrane insertion of MP20 occurs in a discrete transition zone that coincided with the degradation of cell nuclei. To test the significance of the membrane insertion of MP20 to overall lens function, whole lenses were incubated for varying times in a solution containing either Texas Red-dextran or Lucifer yellow as markers of extracellular space. Lenses were fixed and then processed for immunocytochemistry. Analysis of these sections showed that both tracer dyes were excluded from the extracellular space in an area that coincided with insertion of MP20 into the plasma membrane. Our results suggest that the insertion of MP20 into fibre cell membranes coincides with the creation of a barrier that restricts the diffusion of molecules into the lens core via the extracellular space. | |
2001 |
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Gonen, Tamir; Grey, Angus C; Jacobs, Marc D; Donaldson, Paul J; Kistler, Joerg MP20, the second most abundant lens membrane protein and member of the tetraspanin superfamily, joins the list of ligands of galectin-3 Journal Article BMC Cell Biol., 2 (17), 2001. @article{pmid11532191, title = {MP20, the second most abundant lens membrane protein and member of the tetraspanin superfamily, joins the list of ligands of galectin-3}, author = {Tamir Gonen and Angus C Grey and Marc D Jacobs and Paul J Donaldson and Joerg Kistler}, url = {https://cryoem.ucla.edu/wp-content/uploads/gonen_2001.pdf, Main text}, year = {2001}, date = {2001-08-14}, journal = {BMC Cell Biol.}, volume = {2}, number = {17}, abstract = {Although MP20 is the second most highly expressed membrane protein in the lens its function remains an enigma. Putative functions for MP20 have recently been inferred from its assignment to the tetraspanin superfamily of integral membrane proteins. Members of this family have been shown to be involved in cellular proliferation, differentiation, migration, and adhesion. In this study, we show that MP20 associates with galectin-3, a known adhesion modulator. MP20 and galectin-3 co-localized in selected areas of the lens fiber cell plasma membrane. Individually, these proteins purified with apparent molecular masses of 60 kDa and 22 kDa, respectively. A 104 kDa complex was formed in vitro upon mixing the purified proteins. A 102 kDa complex of MP20 and galectin-3 could also be isolated from detergent-solubilized native fiber cell membranes. Binding between MP20 and galectin-3 was disrupted by lactose suggesting the lectin site was involved in the interaction. MP20 adds to a growing list of ligands of galectin-3 and appears to be the first representative of the tetraspanin superfamily identified to possess this specificity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Although MP20 is the second most highly expressed membrane protein in the lens its function remains an enigma. Putative functions for MP20 have recently been inferred from its assignment to the tetraspanin superfamily of integral membrane proteins. Members of this family have been shown to be involved in cellular proliferation, differentiation, migration, and adhesion. In this study, we show that MP20 associates with galectin-3, a known adhesion modulator. MP20 and galectin-3 co-localized in selected areas of the lens fiber cell plasma membrane. Individually, these proteins purified with apparent molecular masses of 60 kDa and 22 kDa, respectively. A 104 kDa complex was formed in vitro upon mixing the purified proteins. A 102 kDa complex of MP20 and galectin-3 could also be isolated from detergent-solubilized native fiber cell membranes. Binding between MP20 and galectin-3 was disrupted by lactose suggesting the lectin site was involved in the interaction. MP20 adds to a growing list of ligands of galectin-3 and appears to be the first representative of the tetraspanin superfamily identified to possess this specificity. | |
2000 |
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Gonen, Tamir; Donaldson, Paul; Kistler, Joerg Galectin-3 Is Associated with the Plasma Membrane of Lens Fiber Cells Journal Article Investigative Ophthalmology and Visual Science, 41 (1), pp. 199–203, 2000. @article{gonen_2000, title = {Galectin-3 Is Associated with the Plasma Membrane of Lens Fiber Cells}, author = {Tamir Gonen and Paul Donaldson and Joerg Kistler}, url = {https://cryoem.ucla.edu/wp-content/uploads/gonen_2000.pdf, Main text}, year = {2000}, date = {2000-01-01}, journal = {Investigative Ophthalmology and Visual Science}, volume = {41}, number = {1}, pages = {199--203}, abstract = {PURPOSE: To discover proteins that have the potential to contribute to the tight packing of fiber cells in the lens. METHODS: Crude fiber cell membranes were isolated from ovine lens cortex. Proteins were separated by two-dimensional gel electrophoresis, and selected protein spots identified by micro-sequencing. The identification of galectin-3 was confirmed by immunoblotting with a specific antibody. The association of galectin-3 with the fiber cell plasma membrane was investigated using immunofluorescence microscopy, solubilization trials with selected reagents, and immunoprecipitation to identify candidate ligands. RESULTS: A cluster of three protein spots with an apparent molecular weight of 31,000 and isoelectric points ranging between 7 and 8.5 were resolved and identified as galectin-3. This protein was associated peripherally with the fiber cell plasma membrane and interacted with MP20, an abundant intrinsic membrane protein that had been identified previously as a component of membrane junctions between fiber cells. CONCLUSIONS: The detection of galectin-3 in the lens is a novel result and adds to the growing list of lens proteins with adhesive properties. Its location at the fiber cell membrane and its association with the junction-forming MP20 is consistent with a potential role in the development or maintenance of the tightly packed lens tissue architecture. (Invest Ophthalmol Vis Sci. 2000;41:199 –203)}, keywords = {}, pubstate = {published}, tppubtype = {article} } PURPOSE: To discover proteins that have the potential to contribute to the tight packing of fiber cells in the lens. METHODS: Crude fiber cell membranes were isolated from ovine lens cortex. Proteins were separated by two-dimensional gel electrophoresis, and selected protein spots identified by micro-sequencing. The identification of galectin-3 was confirmed by immunoblotting with a specific antibody. The association of galectin-3 with the fiber cell plasma membrane was investigated using immunofluorescence microscopy, solubilization trials with selected reagents, and immunoprecipitation to identify candidate ligands. RESULTS: A cluster of three protein spots with an apparent molecular weight of 31,000 and isoelectric points ranging between 7 and 8.5 were resolved and identified as galectin-3. This protein was associated peripherally with the fiber cell plasma membrane and interacted with MP20, an abundant intrinsic membrane protein that had been identified previously as a component of membrane junctions between fiber cells. CONCLUSIONS: The detection of galectin-3 in the lens is a novel result and adds to the growing list of lens proteins with adhesive properties. Its location at the fiber cell membrane and its association with the junction-forming MP20 is consistent with a potential role in the development or maintenance of the tightly packed lens tissue architecture. (Invest Ophthalmol Vis Sci. 2000;41:199 –203) | |
1999 |
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Kistler, Joerg; Merriman-Smith, Rachelle; Young, Miriam; Gonen, Tamir; Cowan, Dougal; Chee, Kaa-Sandra; Lin, Jun Sheng; Green, Colin; Hasler, Lorenz; Engel, Andreas; Donaldson, Paul Molecular Solutions To Tissue Transparency Journal Article N.Z. Biosciences, pp. 35–37, 1999. @article{kistler_1999, title = {Molecular Solutions To Tissue Transparency}, author = {Joerg Kistler and Rachelle Merriman-Smith and Miriam Young and Tamir Gonen and Dougal Cowan and Kaa-Sandra Chee and Jun Sheng Lin and Colin Green and Lorenz Hasler and Andreas Engel and Paul Donaldson}, url = {https://cryoem.ucla.edu/wp-content/uploads/kistler_1999.pdf, Main text}, year = {1999}, date = {1999-08-01}, journal = {N.Z. Biosciences}, pages = {35--37}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Baker, Ted; Metcalf, Peter; Smith, Clyde; Arcus, Vic; Ashton, Rachael; Baker, Heather; Banfield, Mark; Cross, Jenny; Drew, David; Goldstone, David; Gonen, Tamir; Haebel, Peter; Holliss, Caroline; Ivanovich, Ivan; Kagawa, Todd; Kidd, Richard; Koon, Nayden; Leydier, Sabine; Lott, Shaun; McCarthy, Andrew; Nurizzo, Didier; Shewry, Steve; Sigrell, Jill; Sun, Xiaolin More Than Just A Pretty Picture Journal Article N.Z. Biosciences, pp. 32–35, 1999. @article{baker_1999, title = {More Than Just A Pretty Picture}, author = {Ted Baker and Peter Metcalf and Clyde Smith and Vic Arcus and Rachael Ashton and Heather Baker and Mark Banfield and Jenny Cross and David Drew and David Goldstone and Tamir Gonen and Peter Haebel and Caroline Holliss and Ivan Ivanovich and Todd Kagawa and Richard Kidd and Nayden Koon and Sabine Leydier and Shaun Lott and Andrew McCarthy and Didier Nurizzo and Steve Shewry and Jill Sigrell and Xiaolin Sun}, url = {https://cryoem.ucla.edu/wp-content/uploads/baker_1999.pdf, Main text}, year = {1999}, date = {1999-08-01}, journal = {N.Z. Biosciences}, pages = {32--35}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |