CONVERSION FROM OLIGOMERS TO TETRAMERS ENHANCES AUTOPHOSPHORYLATION BY LENS ALPHA-A-CRYSTALLIN - SPECIFICITY BETWEEN ALPHA-A AND ALPHA-B-CRYSTALLIN SUBUNITS

Previously we showed that cu crystallins are autophosphorylated (Kantorow, M., and Piatigorsky, J. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 3112-3116), Here we report that addition of 1% deoxycholate converted alpha A-crystallin aggregates into 80-kDa tetramers which were 16-fold more active for autophosphorylation, Circular dichroism (CD) spectra of alpha-crystallin revealed little or no change in secondary and tertiary structures in 1% deoxycholate, alpha A2D, a truncated form of bovine alpha A that exists as a tetramer, was as active for autophosphorylation in the absence of deoxycholate as intact alpha A was in the presence of deoxycholate, At least one serine between amino acids 131 and 145 of bovine alpha A was auto phosphorylated in peptide mapping experiments, Chicken alpha A-crystallin, which lacks the Ser-122 cAMP-dependent kinase site of bovine alpha A, was also autophosphorylated in the presence of deoxycholate, In contrast to alpha A crystallin, autophosphorylation by alpha B-crystallin was not activated by deoxycholate despite its conversion to a tetrameric form, and alpha B was also more efficiently phosphorylated by cAMP-dependent kinase than alpha A, These data suggest metabolic differences between the alpha-crystallin subunits that may be related to specific expression of alpha A in the lens and ubiquitous expression of alpha B in numerous normal and diseased tissues.