Effect of trifluoroethanol on the structural and functional properties of alpha-crystallin

Alpha crystallin is an eye lens protein with a molecular weight of approximately 800 kDa. It belongs to the class of small heat shock proteins. Besides its structural role, it is known to prevent the aggregation of beta- and gamma-crystallins and several other proteins under denaturing conditions and is thus believed to play an important role in maintaining lens transparency. In this communication, we have investigated the effect of 2,2,2-trifluoroethanol (TFE) on the structural and functional features of the native alpha-crystallin and its two constituent subunits. A conformational change occurs from the characteristic beta-sheet to the alpha-helix structure in both native alpha-crystallin and its subunits with the increase in TFE levels. Among the two subunits, alphaA-crystallin is relatively stable and upon preincubation prevents the characteristic aggregation of alphaB-crystallin at 20% and 30% (v/v) TFE. The hydrophobicity and chaperone-like activity of the crystallin subunits decrease on TFE treatment. The ability of alphaA-crystallin to bind and prevent the aggregation of alphaB-crystallin, despite a conformational change, could be important in protecting the lens from external stress. The loss in chaperone activity of alphaA-crystallin exposed to TFE and the inability of peptide chaperone--the functional site of alphaA-crystallin--to stabilize alphaB-crystallin at 20-30% TFE suggest that the site(s) involved in subunit interaction and chaperone-like function are quite distinct.