Assembly Principles of the Human R2TP Chaperone Complex Reveal the Presence of R2T and R2P Complexes

Abstract

R2TP is a highly conserved chaperone complex formed by two AAA+ ATPases, RUVBL1 and RUVBL2, that associate with PIH1D1 and RPAP3 proteins. R2TP acts in promoting macromolecular complex formation. Here, we establish the principles of R2TP assembly. Three distinct RUVBL1/2‐based complexes are identified: R2TP, RUVBL1/2‐RPAP3 (R2T), and RUVBL1/2‐PIH1D1 (R2P). Interestingly, we find that PIH1D1 does not bind to RUVBL1/RUVBL2 in R2TP and does not function as a nucleotide exchange factor; instead, RPAP3 is found to be the central subunit coordinating R2TP architecture and linking PIH1D1 and RUVBL1/2. We also report that RPAP3 contains an intrinsically disordered N‐terminal domain mediating interactions with substrates whose sequences are primarily enriched for armadillo repeat domains and other helical‐type domains. Our work provides a clear and consistent model of R2TP complex structure and gives important insights into how a chaperone machine concerned with assembly of folded proteins into multisubunit complexes might work.