The trypanosome Rhomboid protease RHBDL4 promotes retrotranslocation of aggregation-prone proteins for degradation

: In the endoplasmic reticulum (ER), the ER-associated degradation (ERAD) pathway targets incorrectly folded and unassembled proteins into the cytoplasm for turnover by the proteasome. Previously, we showed that the ER-resident rhomboid protease RHBDL4, together with p97, mediates membrane protein degradation. However, whether RHBDL4 acts in concert with additional ERAD components is unclear, and its full substrate spectrum remains to be defined. SILAC-based shotgun proteomics and immunoprecipitation experiments revealed that endogenously-tagged RHBDL4 interacts with the ERAD erlin complex. The interaction was validated with immunoprecipitation experiments of endogenous RHBDL4, Erlin1 and Erlin2 to show robust co-purification of the respective interaction partner.