High-Resolution Structural Analysis Shows How Tah1 Tethers Hsp90 to the R2TP Complex

The ubiquitous Hsp90 chaperone participates in snoRNP and RNA polymerase assembly through interaction with the R2TP complex. This complex includes the proteins Tah1, Pih1, Rvb1, and Rvb2. Tah1 bridges Hsp90 to R2TP. Its minimal TPR domain includes two TPR motifs and a capping helix. We established the high-resolution solution structures of Tah1 free and in complex with the Hsp90 C-terminal peptide. The TPR fold is similar in the free and bound forms and we show experimentally that in addition to its solvating/stabilizing role, the capping helix is essential for the recognition of the Hsp90 704EMEEVD709 motif. In addition to Lys79 and Arg83 from the carboxylate clamp, this helix bears Tyr82 forming a π/S-CH3 interaction with Hsp90 M705 from the peptide 310 helix. The Tah1 C-terminal region is unfolded, and we demonstrate that it is essential for the recruitment of the Pih1 C-terminal domain and folds upon binding. [Display omitted] •NMR structures of Tah1 free and in complex with the Hsp90 C-terminal peptide•The Tah1 TPR capping helix is essential for recognition of the Hsp90 704EMEEVD709 motif•Tyr82 in Tah1 helix C forms a π/S-CH3 interaction with M705 of the Hsp90 peptide 310 helix•Unfolded Tah1 C-terminal 19 amino acids are key for in vitro Tah1-Pih1 complex formation What are the factors involved in the assembly of snoRNP and RNA polymerase? Back et al. show the direct interaction between Tah1 protein and Hsp90 chaperone on one hand and Tah1 and Phi1 proteins on the other hand. The high-resolution structure obtained by NMR explains how Hsp90 is recruited by the complex R2TP.