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 bovineS-carboxymethyl α-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 EC50values of 15 μM. 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.