K+ is an indispensable cofactor for GrpE stimulation of ATPase activity of DnaK center dot DnaJ complex from Thermus thermophilus

K+ is an indispensable cofactor for ATPase activity of eukaryotic cytosolic Hsp70 chaperone systems which lack a GrpE homolog, In the case of the bacterial Hsp70 (DnaK) system, GrpE, a nucleotide exchange factor, stimulates ATPase activity but little is known about the effect of K+, Here, we have cloned a grpE gene from a thermophile, Thermus thermophilus, and purified a homodimeric GrpE protein. Using proteins of this bacterium, we found that the GrpE stimulation of ATPase activity of DnaK.DnaJ complex was absolutely dependent on the presence of K+. (C) 1997 Federation of European Biochemical Societies.