@article {45953, title = {MP20, the second most abundant lens membrane protein and member of the tetraspanin superfamily, joins the list of ligands of galectin-3.}, journal = {BMC Cell Biology}, volume = {2}, year = {2001}, month = {2001 - Aug}, pages = {17}, abstract = {

BACKGROUND: 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.

RESULTS: 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.

CONCLUSIONS: 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 = {Animals, Binding Sites, Cell Membrane, Eye Proteins, Galectin 3, Lectins, Lens, Crystalline, Ligands, Macromolecular Substances, Membrane Proteins, Rats}, issn = {1471-2121}, doi = {10.1186/1471-2121-2-17}, author = {Gonen, T and Grey, A C and Jacobs, M D and Donaldson, P J and Kistler, J} } @article {45952, title = {Galectin-3 is associated with the plasma membrane of lens fiber cells.}, journal = {Investigative Ophthalmology \& Visual Science}, volume = {41}, year = {2000}, month = {2000 Jan}, 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.

}, keywords = {Amino Acid Sequence, Animals, Antigens, Differentiation, Cell Membrane, Chromatography, High Pressure Liquid, Electrophoresis, Gel, Two-Dimensional, Eye Proteins, Galectin 3, Immunoblotting, Lens Cortex, Crystalline, Ligands, Membrane Glycoproteins, Microscopy, Fluorescence, Molecular Sequence Data, Rabbits, Sequence Homology, Amino Acid, Sheep}, issn = {0146-0404}, author = {Gonen, T and Donaldson, P and Kistler, J} }