SGTA interacts with the proteasomal ubiquitin receptor Rpn13 via a carboxylate clamp mechanism

YesThe fate of secretory and membrane proteins that mislocalize to the cytosol is decided by a collaboration between cochaperone SGTA (small, glutamine-rich, tetratricopeptide repeat protein alpha) and the BAG6 complex, whose operation relies on multiple transient and subtly discriminated interactions with diverse binding partners. These include chaperones, membrane-targeting proteins and ubiquitination enzymes. Recently a direct interaction was discovered between SGTA and the proteasome, mediated by the intrinsic proteasomal ubiquitin receptor Rpn13. Here, we structurally and biophysically characterize this binding and identify a region of the Rpn13 C-terminal domain that is necessary and sufficient to facilitate it. We show that the contact occurs through a carboxylate clamp-mediated molecular recognition event with the TPR domain of SGTA, and provide evidence that the interaction can mediate the association of Rpn13 and SGTA in a cellular context.RLI was supported by MRC New Investigator Research Grant: G0900936. RLI and SH are funded by BBSRC grants: BB/L006952/1 and BB/L006510/1 respectively. RLI is funded by BBSRC grant: BB/N006267/1. AT is funded by BBSRC grant: BB/J014567/1. ILT was the recipient of a Wellcome Trust Vacation Scholarship 2015. NMR experiments were performed at the Centre for Biomolecular Spectroscopy, King’s College London, established with a Capital Award from the Wellcome Trus

Mice lacking WRB reveal differential biogenesis requirements of tail-anchored proteins in vivo

Tail-anchored (TA) proteins are post-translationally inserted into membranes. The TRC40 pathway targets TA proteins to the endoplasmic reticulum via a receptor comprised of WRB and CAML. TRC40 pathway clients have been identified using in vitro assays, however, the relevance of the TRC40 pathway in vivo remains unknown. We followed the fate of TA proteins in two tissue-specific WRB knockout mouse models and found that their dependence on the TRC40 pathway in vitro did not predict their reaction to receptor depletion in vivo. The SNARE syntaxin 5 (Stx5) was extremely sensitive to disruption of the TRC40 pathway. Screening yeast TA proteins with mammalian homologues, we show that the particular sensitivity of Stx5 is conserved, possibly due to aggregation propensity of its cytoplasmic domain. We establish that Stx5 is an autophagy target that is inefficiently membranetargeted by alternative pathways. Our results highlight an intimate relationship between the TRC40 pathway and cellular proteostasis.peerReviewe