Hsp105 but not Hsp70 family proteins suppress the aggregation of heat‐denatured protein in the presence of ADP

Hsp105α and Hsp105β are mammalian members of the Hsp105/110 family, a diverged subgroup of the Hsp70 family. Here, we show that Hsp105α and Hsp105β bind non‐native protein through the β‐sheet domain and suppress the aggregation of heat‐denatured protein in the presence of ADP rather than ATP. In contrast, Hsc70/Hsp40 suppressed the aggregation of heat‐denatured protein in the presence of ATP rather than ADP. Furthermore, the overexpression of Hsp105α but not Hsp70 in COS‐7 cells rescued the inactivation of luciferase caused by ATP depletion. Thus, Hsp105/110 family proteins are suggested to function as a substitute for Hsp70 family proteins to suppress the aggregation of denatured proteins in cells under severe stress, in which the cellular ATP level decreases markedly.