Characterization of the L399P and R447G mutants of hsc70: the decrease in refolding activity is correlated with an increase in the rate of substrate dissociation.

It is known that 70-kDa heat-shock cognate protein (hsc70) is capable of forming complexes with unfolded polypeptide substrates and works with DnaJ homologues to refold denatured proteins. Herein, we characterized two hsc70 mutants, hsc70(L399P) and hsc70(R447G). They retained the capability of restoring the activity of denatured luciferase, but their activity was decreased to 40% and 20%, respectively, of that of hsc70. The rate of dissociation for the heptapeptide substrate FYQLALT from the mutants was increased, and the R447G mutant had the faster rate of peptide dissociation. Thus, the reduction in the ability of these mutants to refold denatured proteins was correlated with an increase in the rate of substrate dissociation.