Molecular chaperone properties of the high molecular weight aggregate from aged lens

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Abstract
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 compared with the lower molecular weight, oligomeric fraction of α isolated from the same lens. Although the major components of both fractions were the α-A and α-B chains, the HMWA fraction possessed a decreased ability to protect other proteins against heat-induced denaturation and aggregation. Immunoelectron microscopy of both fractions demonstrated that α particles from the HMWA fraction contained increased amounts of β and γ crystallins, bound to a central region of the supramolecular complex. Together, these results demonstrate that α crystallins found in the HMWA fraction possess a decreased ability to protect against heat-induced denaturation and aggregation, and suggest that at least part of this decrease could be due to the increased presence of β and γ crystallins complexed to the putative chaperone receptor site of the α particles.