MOLECULAR CHAPERONE PROPERTIES OF THE HIGH-MOLECULAR-WEIGHT AGGREGATEFROM AGED LENS

The high molecular weight aggregate (HMWA) fraction was isolated from the water soluble proteins of aged bovine lenses. Its composition and ability to inhibit heat-induced denaturation and aggregation were comp ared with the lower molecular weight, oligomeric fraction of a isolate d from the same lens. Although the major components of both fractions were the alpha-A and alpha-B chains, the HMWA fraction possessed a dec reased ability to protect other proteins against heat-induced denatura tion and aggregation. Immunoelectron microscopy of both fractions demo nstrated that a particles from the HMWA fraction contained increased a mounts of beta and gamma crystallins, bound to a central region of the supramolecular complex. Together, these results demonstrate that ct c rystallins found in the HMWA fraction possess a decreased ability to p rotect against heat-induced denaturation and aggregation, and suggest that at least part of this decrease could be due to the increased pres ence of beta and gamma crystallins complexed to the putative chaperone receptor site of the a particles.