Binding of denatured protein decreases the chaperone properties of alpha crystallin

Previous studies have demonstrated that partially denatured forms of the beta and gamma crystallins preferentially bind to a central region of the alpha crystallin particle, both in vitro and in vivo. These experiments were designed to ascertain if binding of a partially denatured protein to alpha crystallin could result in a diminished ability of alpha crystallin to protect against further protein denaturation and aggregation. A constant amount of alpha crystallin was incubated with increasing amounts of purified gamma s crystallin and then heated at 65 degrees C for 45 min. Under these conditions, the partially denatured gamma s crystallin binds to alpha crystallin. The resulting complexes were tested for their ability to protect against heat-induced denaturation and aggregation of alcohol dehydrogenase heated at 44 degrees C. As increasing amounts of partially denatured gamma s bound to alpha crystallin, the resulting complexes possessed a decreased ability to protect against heat-induced denaturation and aggregation. These results demonstrate that binding of partially denatured forms of a purified protein to alpha crystallin results in a complex with decreased ability to protect against denaturation, suggesting a possible mechanism whereby the molecular chaperone properties of alpha crystallin may be diminished in vivo.