THE C-TERMINAL REGION OF ALPHA-CRYSTALLIN - INVOLVEMENT IN PROTECTIONAGAINST HEAT-INDUCED DENATURATION

Recent studies have demonstrated that the alpha-crystallins can protec t other proteins against heat-induced denaturation and aggregation. To determine the possible involvement of the C-terminal region in this a ctivity, the alpha-crystallins were subjected to limited tryptic diges tion, and the amount of cleavage from the N-terminal and C-terminal re gions of the alpha-A and alpha-B crystallin chains was assessed using antisera specific for these regions. Limited tryptic digestion resulte d in cleavage only from the C-terminal region of alpha-A crystallin. T his trypsin-treated alpha-A crystallin preparation showed a decreased ability to protect proteins from heat-induced aggregation using an in vitro assay. Together, these results demonstrate that the C-terminal r egion of alpha-A crystallin is important for its ability to protect ag ainst heat-induced aggregation, which is consistent with the hypothesi s that post-translational changes that are known to occur at the C-ter minal region may have significant effects on the ability of alpha-A cr ystallin to protect against protein denaturation in vivo.