Dissociation of human alpha B-crystallin aggregates by thiocyanate is structurally and functionally reversible

Conformational modifications and changes in the aggregation state of human alpha B-crystallin were investigated at different concentrations of SDS, KB r, urea, and NH4SCN and at different temperatures. Intrinsic fluorescence m easurements indicated complete and reversible unfolding of the proteid at 2 M NH4SCN, whereas the concentration of urea required for complete and irre versible unfolding was 6 M. Gel permeation chromatography indicated almost complete dissociation of the micellelike aggregate of alpha B-crystallin in 2 M NH4SCN, but only partial dissociation into large-sized aggregates in 6 M urea. Thiocyanate-treated alpha B-crystallin recovered its chaperone-lik e activity upon dilution of the dissociating agent, whereas the urea-treate d protein did not.