Advances on the Structure of the R2TP/Prefoldin-like Complex

Abstract

Cellular stability, assembly and activation of a growing list of macromolecular complexes require the action of HSP90 working in concert with the R2TP/Prefoldinlike (R2TP/PFDL) co-chaperone. RNA polymerase II, snoRNPs and complexes of PI3kinase-like kinases, a family that includes the ATM, ATR, DNA-PKcs, TRAPP, SMG1 and mTOR proteins, are among the clients of the HSP90-R2TP system. Evidence links the R2TP/PFDL pathway with cancer, most likely because of the essential role in pathways commonly deregulated in cancer. R2TP forms the core of the co-cochaperone and orchestrates the recruitment of HSP90 and clients, whereas prefoldin and additional prefoldin-like proteins, including URI, associate with R2TP, but their function is still unclear. The mechanism by which R2TP/PFLD facilitates assembly and activation of such a variety of macromolecular complexes is poorly understood. Recent efforts in the structural characterization of R2TP have started to provide some mechanistic insights. We summarize recent structural findings, particularly how cryo-electron microscopy (cryo-EM) is contributing to our understanding of the architecture of the R2TP core complex. Structural differences discovered between yeast and human R2TP reveal unanticipated complexities of the metazoan R2TP complex, and opens new and interesting questions about how R2TP/PFLD works.

Role of the Novel Hsp90 Co-Chaperones in Dynein Arms’ Preassembly

“…The RPAP3-PIH1D1 heterodimer is an integral and specific component of R2TP and likely regulates the enzymatic activity of RuvBL1 and RuvBL2 [25]. The RuvBL1 and RuvBL2 AAA ATPases, due to their enzymatic activity, form the catalytic component of the R2TP complex, probably acting not only as co-chaperone but also as a chaperone [26]. The N-terminal region of PIH1D1 ( Figure 2) has the conserved PIH1 domain (protein interacting with heat shock protein 90) known to mediate the binding of proteins containing a specific motif phosphorylated by casein kinase 2 (CK2) [40][41][42].…”

Structure of the TELO2-TTI1-TTI2 complex and its function in TOR recruitment to the R2TP chaperone

“…While our data suggest that TTT also plays a role in regulating the ATPase activity of the R2 ring, its main function is believed to be as an adaptor, recruiting PIKK client proteins such as TOR to the R2TP or R2 complex (Houry et al, 2018; Kakihara and Houry, 2012; Munoz-Hernandez et al, 2018). To test this, we purified S.cerevisiae TTT in which Tti1p carried a C-terminal flag-tag, and looked at its ability to interact with a TOR1-Lst8 complex from the closely related yeast Kluveromyces marxianus (construct a kind gift of Roger Williams, MRC-LMB, Cambridge) which has 83% sequence similarity to S.cerevisiae TOR2, but is far more amenable to large scale expression and purification.…”

“…The heterohexameric RUVBL1-RUVBL2 ring appears to provide the central constant component of a multiplicity of chaperone complexes each specific for a distinct class of client proteins (Houry et al, 2018; Kakihara and Houry, 2012; Munoz-Hernandez et al, 2018). As with systems such as HSP90, with which RUVBL1-RUVBL2 (R2) collaborates as a co-chaperone, client specificity is believed to be mediated by scaffold proteins that structurally couple the generalised core R2-ATPase complex to the client.…”

The Mammalian Ecdysoneless Protein Interacts with RNA Helicase DDX39A To Regulate Nuclear mRNA Export

“…ECD's previously established interaction with the PIH1D1 and RUVBL1 components of the R2TP co-chaperone complex (37) may allow it to play an even broader role in RNA biogenesis. The R2TP complex is known to promote the assembly small nucleolar ribonucleoproteins (snoRNPs) (34,35,(68)(69)(70)(71)(72)(73). Notably, ECD was also reported to interact with ZINHIT2 protein, which was shown to function as a mediator of R2TP/Prefoldin-like cochaperone interaction with the U5 snRNP (34,72), a central component of the spliceosome (35).…”