Molecular chaperone-like activity of Alpha-Crystallin

Abstract

Eye lens is a transparent, highly refractive tissue that focuses light to form images on newlinethe retina. Eye lens is surrounded by a capsule. A single layer of epithelial cells in the newlineposterior region grow and differentiate into elongated fibre cells and pack tightly. These fibre newlinecells contain proteins called crystallins at high concentrations. The concentration of crystallins newlinein these fibre cells ranges from 200-500 mg/ml. It is believed that inter-crystallin interactions newlineand spatial distribution of crystallins across lens make it transparent and correct for spherical newlineaberrations. There is very little protein turn:over in the lens. Thus all post-translational newlinemodifications in the crystallins accumulate leading to age-related problems. These newlinemodifications alter the stability and solubility of these proteins. Thus investigating structural newlineand stability aspects of crystallins is necessary to understand the molecular basis of lens newlinetransparency, the loss of which results in cataract. newlineMammalian eye lens crystallins are classified as a-, ~- and y- crystallins based on their newlineamino acid sequence and immunological properties. Until recently it was believed that these newlinecrystallins are specific to lens and play only a structural role. However, recent studies have newlineshown that a-crystallin is expressed in non-lenticular tissues such as heart, kidne¥ and brain newlineparticularly under stress or disease conditions .. It is also shown that a-crystallin has sequence newlinehomology with small heat shock proteins. newlinea-Crystallin, a multimeric protein, is shown to prevent aggregation of oth,er proteins. newlineThis property is similar to that of molecular chaperones - a class of unrelated proteins which newlineprevent aggregation of non-native structures of proteins, keep them in a folding competent state newlineand enhance their folding yield. newlineThis work is undertaken to investigate the structure and molecular mechanism of the newlinechaperone-like activity of a-crystallin. The first chapter of the thesis presents an overview of newlinethe eye lens and crystallins.