A comprehensive view of molecular chaperone function in the cell was obtained through a systematic global integrative network approach based on physical (protein-protein) and genetic (gene-gene or epistatic) interaction mapping. This allowed us to decipher interactions involving all core chaperones (67) and cochaperones (15) of Saccharomyces cerevisiae. Our analysis revealed the presence of a large chaperone functional supercomplex, which we named the naturally joined (NAJ) chaperone complex, encompassing Hsp40, Hsp70, Hsp90, AAA+, CCT, and small Hsps. We further found that many chaperones interact with proteins that form foci or condensates under stress conditions. Using an in vitro reconstitution approach, we demonstrate condensate formation for the highly conserved AAA+ ATPases Rvb1 and Rvb2, which are part of the R2TP complex that interacts with Hsp90. This expanded view of the chaperone network in the cell clearly demonstrates the distinction between chaperones having broad versus narrow substrate specificities in protein homeostasis.
Bibliographical noteFunding Information:
We thank Dr. Craig Smibert (University of Toronto) for the pRS116 DHH1 plasmid, Dr. Judith Frydman (Stanford University) for pESC GFP-VHL plasmid, Dr. Guri Giaever (University of British Columbia) for the RVB1/rvb1 Δ and RVB2/rvb2 Δ diploid strains, and Dr. Grant Brown (University of Toronto) for the NUP49-mCHERRY strain. K.R. was supported by a Canadian Institutes of Health Research (CIHR) Training Program in Protein Folding and Interaction Dynamics: Principles and Diseases fellowship and by a University of Toronto Fellowship from the Department of Biochemistry. J.H. was supported by a Natural Sciences and Engineering Research Council of Canada PGSD2 fellowship. T.V.S. was supported by a CNPq-Brazil fellowship ( 202192/2015-6 ) and a Saskatchewan Health Research Foundation postdoctoral fellowship. M.B. holds a CIHR New Investigator award. C.B. and C.L.M. are fellows of the Canadian Institute for Advanced Research (CIFAR) . This work was partially supported by the National Institutes of Health ( R01HG005853 to CB and CLM and R01HG005084 to CLM). This work was also supported by CIHR (RSN-124512, MOP-125952, RSN-132191, and FDN-154318 to M.B., MOP-93778 to W.A.H., and MOP-81256 to I.S. and W.A.H.).
- NAJ chaperone complex
- chaperone network
- genetic interaction profiles
- genetic interactions
- perinuclear condensate
- physical interactions