Differential effects of molecular chaperones on refolding of homologous proteins

Three homologous aspartate aminotransferases with virtually identical spatial structures and pairwise amino acid sequence identities of > 40% differ markedly with respect to the yield of renaturation upon dilution from 6 M guanidine hydrochloride (mitochondrial << cytosolic < Escherichia coli). The enzymes also respond differently to molecular chaperones. GroEL/GroES, the Hsp60 homolog of E. coli, increased considerably the yield of renaturation of mitochondrial aspartate aminotransferase and to a lesser extent that of its cytosolic counterpart, but not that of the E. coli enzyme. DnaK/DnaJ/GrpE, the Hsp70 system of E. coli, also increased the yield of renaturation of mitochondrial aspartate aminotransferase. Apparently, specific features in the amino acid sequence or the folding pathway which are independent of the final secondary and tertiary structure determine the interactions of the folding proteins with the chaperone systems.