The disaggregation activity of the mitochondrial ClpB homolog Hsp78 maintains Hsp70 function during heat stress.
Molecular chaperones are important components of mitochondrial protein biogenesis and are required to maintain the organellar function under normal and stress conditions. We addressed the functional role of the Hsp100/ClpB homolog Hsp78 during aggregation reactions and its functional cooperation with the main mitochondrial Hsp70, Ssc1, in mitochondria of the yeast Saccharomyces cerevisiae. By establishing an aggregation/disaggregation assay in intact mitochondria we demonstrated that Hsp78 is indispensable for the resolubilization of protein aggregates generated by heat stress under in vivo conditions. The ATP-dependent disaggregation activity of Hsp78 was capable of reversing the preprotein import defect of a destabilized mutant form of Ssc1. This role in disaggregation of Ssc1 is unique for Hsp78, since the recently identified, Hsp70-specific chaperone Zim17 had no effect on the resolubilization reaction. We observed only a minor effect of the second mitochondrial Hsp100 family member Mcx1 on protein disaggregation. A "holding" activity of the mitochondrial Hsp70 system was a prerequisite for a successful resolubilization of aggregated proteins. We conclude that the protective role of Hsp78 in thermotolerance is mainly based on maintaining the molecular chaperone Ssc1 in a soluble and functional state.
von Janowsky
Birgit
B
Institut für Biochemie und Molekularbiologie, Hermann-Herder-Str. 7, Universität Freiburg, 79104 Freiburg, Germany.
Major
Tamara
T
Knapp
Karin
K
Voos
Wolfgang
W
D049069:ATP-Dependent Proteases; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000502:physiology; D049071:Endopeptidase Clp / Q000737:chemistry* / Q000235:genetics; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000502:physiology*; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D006358:Hot Temperature; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000502:physiology; D018832:Molecular Chaperones / Q000235:genetics / Q000502:physiology; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D012697:Serine Endopeptidases / Q000502:physiology; D012995:Solubility
D018840:HSP70 Heat-Shock Proteins; C083349:HSP78 protein, S cerevisiae; D006360:Heat-Shock Proteins; C115923:Mcx1 protein, S cerevisiae; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; C101767:SSC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C495990:Zim17 protein, S cerevisiae; D049069:ATP-Dependent Proteases; C085155:PIM1 protein, S cerevisiae; D012697:Serine Endopeptidases; D049071:Endopeptidase Clp; D000252:Calcium-Transporting ATPases