Proteins interacting with the molecular chaperone hsp70/hsc70: physical associations and effects on refolding activity.

We investigated several hsp70/hsc70 interacting proteins and established by two independent techniques that hsp40 and Hop/p60 specifically interact with the 257 residue carboxy-terminal domain of hsp70 while Hap-46 and Hip/p48 bind the 383 residue amino-terminal ATP binding domain. Hap-46 and Hip/p48 competed for binding to hsc70, while Hap-46 had no effect on the binding of either Hop/p60 or hsp40 to hsc70. Hap-46 inhibited the refolding of thermally denatured firefly luciferase in an hsc70 and hsp40 dependent assay, and this effect was largely compensated by Hop/p60. These interacting proteins thus appear to cooperate in affecting the chaperoning activity of hsp70/hsc70.