title: alpha-Crystallin chaperone-like activity and membrane binding in age-related cataracts.
abstract: alpha-Crystallin, the major protein component of the vertebrate lens, is thought to play a critical role in the maintenance of transparency through its ability to inhibit stress-induced protein aggregation. However, during aging and cataract formation the amount of membrane-bound alpha-crystallin increases significantly while high molecular weight complexes (HMWCs) comprised of alpha-crystallin and other lens crystallins accumulate. These and other recent data suggest a possible link between cataract formation, the formation of high molecular weight alpha-crystallin aggregates, and the progressive increase in membrane association of alpha-crystallin. To better understand these processes, we characterized the chaperone-like activity (CLA) and subunit exchange of membrane bound alpha-crystallin. In addition, we measured the membrane binding properties of in vitro constituted HMWCs to understand the mechanism by which increased alpha-crystallin is bound to the membrane of old and cataractous lens cells in vivo. Membrane-associated alpha-crystallin complexes have measurably reduced CLA compared to complexes in solution; however, membrane binding does not alter the time required for alpha-crystallin complexes to reach subunit exchange equilibrium. In addition, HMWCs prepared in vitro have a profoundly increased membrane binding capacity as compared to native alpha-crystallin. These results are consistent with a model in which increased membrane binding of alpha-crystallin is an integral step in the pathogenesis of many forms of cataracts.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Cobb
authors.forename: J Mark
authors.initials: JM
authors.lastname: Petrash
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000375:Aging; D000818:Animals; D002386:Cataract / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003459:Crystallins / Q000737:chemistry*; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000494:pharmacology; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry / Q000378:metabolism; D050356:Lipid Metabolism; D008954:Models, Biological; D018832:Molecular Chaperones / Q000737:chemistry; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D013109:Sphingomyelins / Q000737:chemistry; D013997:Time Factors
chemical_list: D003459:Crystallins; D005456:Fluorescent Dyes; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D013109:Sphingomyelins; D015060:1,2-Dipalmitoylphosphatidylcholine