Interaction of human recombinant alpha A- and alpha B-crystallins with early and late unfolding intermediates of citrate synthase on its thermal denaturation

We have investigated the role of recombinant human alphaA- and alphaB-cryst allins in the heat-induced inactivation and aggregation of citrate synthase , Homo-multimers of both alphaA- and alphaB-crystallins confer protection a gainst heat-induced inactivation in a concentration-dependent manner and al so prevent aggregation. Interaction of crystallins with early unfolding int ermediates of citrate synthase reduces their partitioning into aggregation- prone intermediates, This appears to result in enhanced population of early unfolding intermediates that can be reactivated by its substrate, oxaloace tate, Both these homo-multimers do not form a stable complex with the early unfolding intermediates, However, they can form a soluble, stable complex with aggregation-prone late unfolding intermediates. This soluble complex f ormation prevents aggregation. Thus, it appears that the chaperone activity of alpha -crystallin involves both transient and stable interactions depen ding on the nature of intermediates on the unfolding pathway; one leads to reactivation of the enzyme activity while the other prevents aggregation. ( C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.