The type I Hsp40 zinc finger-like region is required for Hsp70 to capture non-native polypeptides from Ydj

The cytosolic yeast Hsp40 Ydj1 contains a conserved zinc finger-like region (ZFLR), which has two zinc-binding domains (ZBD), that helps regulate and specify Hsp70 function. To investigate the mechanism for Ydj1 ZFLR action, ZBDI and ZBDII mutants were constructed and characterized. ZBDII mutants exhibited temperature-sensitive growth defects, but yeast tolerated mutation of ZBDI. However, ZBDI and ZBDII mutants were defective at facilitating androgen receptor (AB.) folding. Defective AR folding was associated with the accumulation of complexes between AR and Ydj1 ZFLR mutants and a reduction in Hsp70·AR complex formation. Purified Ydj1 ZBDI and ZBDII mutants could bind non-native polypeptides but could not deliver luciferase to Hsp70 and were defective at luciferase refolding. Interestingly, the ability of Ydj1 to synergize with Hsp70 to suppress thermally induced protein aggregation was blocked by mutation of ZBDII, but not ZBDI. Hence, ZBDII is required for yeast to survive heat stress because it is essential for Ydj1 to cooperate with Hsp70 to suppress protein aggregation. On the other hand, protein folding is dependent upon the action of both ZBDI and ZBDII because each is required for Hsp70 to capture non-native polypeptides from Ydj1.