Chaperone-like activity of bovine lens alpha-crystallin in the presence ofdithiothreitol-destabilized proteins: Characterization of the formed complexes

Since alpha-crystallin was shown to have in vitro chaperone-like activity, its structure-function relationship has been extensively studied. However, the mechanism of this function is poorly understood. In this study, we moni tored the interaction of alpha-crystallin with different proteins namely th e insulin B-chain (3.382 kDa), lysozyme (14.4 kDa), and conalbumin (86.18 k Da), all destabilized by dithiothreitol. We found that at 4 degrees C alpha -crystallin prevents the aggregation of destabilized insulin. During the ti me course of the interaction of alpha-crystallin with the substrate protein , we observed three classes of molecules: the monomeric protein and monomer ic alpha-crystallin peptides, alpha-crystallin/substrate protein complexes with a size comparable to alpha-crystallin and large particles. The latter are responsible for the increase of the light scattering of solutions, cont aining alpha-crystallin/destabilized protein complexes. The molecular excha nge between the different populations is temperature dependent and seems to be ruled by the kinetics of the structural changes of the destabilized pro teins. At the end all monomeric species are transformed to larger aggregate s. The large complexes are enriched in destabilized proteins, compared to t he initial ratio alpha-crystallin/substrate protein. (C) 2000 Academic Pres s.