Involvement of the 10-kDa C-terminal fragment of hsc70 in complexing with unfolded protein.

Using native gel electrophoresis, we demonstrate that both bovine brain hsc70 and recombinant rat hsc70 form a tightly associated complex with bovine S-carboxymethyl alpha-lactalbumin (CMLA). The formation of the complexes can be inhibited by an octapeptide (KLALSLHD). The recombinant C-terminal 30-kDa fragment also can be tightly associated with CMLA. Consequently, the 44-kDa ATPase domain of hsc70 plays a small role in the formation of the hsc70/CMLA. The N-terminal 60-kDa fragment of hsc70 cannot form a similar complex, despite the finding that the hydrolysis of ATP both by hsc70 and by the 60-kDa fragment can be stimulated by CMLA in a similar concentration-dependent manner with EC50 values of 15 microM. Moreover, the C-terminal 10-kDa fragment of hsc70 cannot tightly associate with CMLA, indicating that this fragment is necessary but not sufficient for the formation of the hsc70/CMLA complex.