Hydrophobic dye inhibits aggregation of molten carbonic anhydrase during thermal unfolding and refolding

Association-seeking surfaces on partially structured polypeptides can participate in interactions that are either intramolecular (folding related) or intermolecular (aggregative). During heat shock, intermolecular associations leading to aggregation are prevented through the binding of such surfaces by chaperones of the Hsp20 family (with Hsp70 later effecting release and refolding). Here we report that the hydrophobic dye, 8-anilino-1-naphthalenesulfonate (ANS), mimics the function of the chaperones in its interactions with molten carbonic anhydrase (CA). At 150-fold molar excess of dye over protein, heat-induced aggregation of CA is almost completely inhibited by binding of ANS to solvent-exposed clusters of nonpolar residues. After exposure of ANS-containing protein solutions to temperatures as high as 95 degrees C, refolded CA can be recovered through cooling and dialysis, with no accompanying aggregation. This apparent mimicking of chaperone activity by a small dye opens up new approaches to understanding and manipulating protein aggregation.