Binding of Denatured Protein Decreases the Chaperone Properties of α Crystallin

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