Substrate transfer from the chaperone Hsp70 to Hsp90.
Hsp90 is an essential chaperone protein in the cytosol of eukaryotic cells. It cooperates with the chaperone Hsp70 in defined complexes mediated by the adaptor protein Hop (Sti1 in yeast). These Hsp70/Hsp90 chaperone complexes play a major role in the folding and maturation of key regulatory proteins in eukaryotes. Understanding how non-native client proteins are transferred from one chaperone to the other in these complexes is of central importance. Here, we analyzed the molecular mechanism of this reaction using luciferase as a substrate protein. Our experiments define a pathway for luciferase folding in the Hsp70/Hsp90 chaperone system. They demonstrate that Hsp70 is a potent capture device for unfolded protein while Hsp90 is not very efficient in this reaction. When Hsp90 is absent, in contrast to the in vivo situation, Hsp70 together with the two effector proteins Ydj1 and Sti1 exhibits chaperone activity towards luciferase. In the presence of the complete chaperone system, Hsp90 exhibits a specific positive effect only in the presence of Ydj1. If this factor is absent, the transferred luciferase is trapped on Hsp90 in an inactive conformation. Interestingly, identical results were observed for the yeast and the human chaperone systems although the regulatory function of human Hop is completely different from that of yeast Sti1.
Wegele
Harald
H
Department of Chemistry, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany.
Wandinger
Sebastian K
SK
Schmid
Andreas B
AB
Reinstein
Jochen
J
Buchner
Johannes
J
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D006360:Heat-Shock Proteins; D006801:Humans; D008156:Luciferases / Q000737:chemistry / Q000378:metabolism; D046912:Multiprotein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D046912:Multiprotein Complexes; C542289:STI1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D008156:Luciferases; D000251:Adenosine Triphosphatases; C095973:SSA1 protein, S cerevisiae