Résumé
R2TP is an HSP90 co-chaperone that assembles important macro-molecular machineries. Itis composed of an RPAP3-PIH1D1 heterodimer, which binds the two essential AAA+ATPasesRUVBL1/RUVBL2. Here, we resolve the structure of the conserved C-terminal domain ofRPAP3, and we show that it directly binds RUVBL1/RUVBL2 hexamers. The human genomeencodes two other proteins bearing RPAP3-C-terminal-like domains and three containingPIH-like domains. Systematic interaction analyses show that one RPAP3-like protein, SPAG1,binds PIH1D2 and RUVBL1/2 to form an R2TP-like complex termed R2SP. This co-chaperoneis enriched in testis and among 68 of the potential clients identified, some are expressed intestis and others are ubiquitous. One substrate is liprin-α2, which organizes large signalingcomplexes. Remarkably, R2SP is required for liprin-α2 expression and for the assembly ofliprin-α2 complexes, indicating that R2SP functions in quaternary protein folding. Effects arestronger at 32 °C, suggesting that R2SP could help compensating the lower temperate of testis.