Study of the chaperoning mechanism of bovine lens alpha-crystallin, a member of the alpha-small heat shock superfamily

We have studied the interaction between lysozyme, destabilized by reducing its -S-S- bonds, and bovine eye lens alpha -crystallin, a member of the alp ha -small heat shock protein superfamily. We have used gel filtration, phot on correlation spectroscopy, and analytical ultracentrifugation to study th e binding of lysozyme by alpha -crystallin at 25 degreesC and 37 degreesC. We can conclude that alpha -crystallin chaperones the destabilized protein in a two-step process. First the destabilized proteins are bound by the alp ha -crystallin so that nonspecific aggregation of the destabilized protein is prevented. This complex is unstable, and a reorganization and inter-part icle exchange of the peptides result in stable and soluble large particles. alpha -Crystallin does not require activation by temperature for the first step of its chaperone activity as it prevents the formation of nonspecific aggregates at 25 degreesC as well as at 37 degreesC. The reorganization of the peptides, however, gives rise to smaller particles at 37 degreesC than at 25 degreesC. indirect evidence shows that the association of several al pha -crystallin/substrate protein complexes leads to the formation of very large particles. These are responsible for the increase of the light scatte ring.