RNF185 destabilizes specific membrane proteins that span all ERAD branches

The endoplasmic reticulum (ER) is the primary site of eukaryotic membrane protein synthesis and quality control, which largely relies on ER-associated degradation (ERAD) to eliminate aberrant nascent proteins. In yeast, two ubiquitin ligases target proteins for ERAD based on aberrancies in substrate transmembrane (ERAD-M), lumenal (ERAD-L), or cytosolic (ERAD-C) domains. How an expanded repertoire of mammalian ERAD factors selects substrates across these classifications is unclear. Here, we show that the human ER-resident RNF185 ubiquitin ligase complex destabilizes a small but specific set of membrane proteins that span all three ERAD branches. Comparisons of three single-pass membrane proteins destabilized by RNF185 identify ERAD-M features in misoriented CHST10, ERAD-C features in unassembled SRPRB, and N-linked glycosylation-dependent ERAD-L features in ATP1B2. Our findings identify RNF185-destabilized membrane proteins with distinct aberrancies that collectively encompass all canonical ERAD substrate classifications and unexpectedly diverse quality control defects.