Quantitative proteomics links the LRRC59 interactome to mRNA translation on the ER membrane

Abstract

Protein synthesis on the endoplasmic reticulum (ER) requires the dynamic coordination of resident membrane proteins and cytoplasmic translation factors. While ER membrane proteins functioning in ribosome association, mRNA anchoring, and protein translocation, have been identified, little is known regarding the higher order organization of ER-localized translation. Here we utilized proximity proteomics to identify neighboring protein networks for the ribosome interactors SEC61{beta}, RPN1, SEC62, and LRRC59. Whereas the SEC61{beta} and RPN1 BioID reporters revealed translocon-associated networks, the SEC62 and LRRC59 reporters identified divergent interactome networks of previously unexplored functions. Notably, the SEC62 interactome is enriched in redox-linked proteins and ER luminal chaperones, whereas the LRRC59 interactome is enriched in SRP pathway components, translation factors, and ER-localized RNA-binding proteins. Analysis of the LRRC59 interactome by native immunoprecipitation identified similar protein and functional enrichments. Combined, these data reveal a functional domain organization for the ER and suggest a key role for LRRC59 in the organization of mRNA translation on the ER. SummaryHannigan et al. characterize the protein interactomes of four ER ribosome-binding proteins, providing evidence that ER-bound ribosomes reside in distinct molecular environments. Their data link SEC62 to ER redox regulation and chaperone trafficking, and suggest a role for LRRC59 in SRP-coupled protein synthesis.