Study of the Chaperoning Mechanism of Bovine Lens α-Crystallin, a Member of the α-Small Heat Shock Superfamily

Abstract

We have studied the interaction between lysozyme, destabilized by reducing its -S-S- bonds, and bovine eye lens α-crystallin, a member of the α-small heat shock protein superfamily. We have used gel filtration, photon correlation spectroscopy, and analytical ultracentrifugation to study the binding of lysozyme by α-crystallin at 25°C and 37°C. We can conclude that α-crystallin chaperones the destabilized protein in a two-step process. First the destabilized proteins are bound by the α-crystallin so that nonspecific aggregation of the destabilized protein is prevented. This complex is unstable, and a reorganization and inter-particle exchange of the peptides result in stable and soluble large particles. α-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°C as well as at 37°C. The reorganization of the peptides, however, gives rise to smaller particles at 37°C than at 25°C. Indirect evidence shows that the association of several α-crystallin/substrate protein complexes leads to the formation of very large particles. These are responsible for the increase of the light scattering.