The OS9 protein is a lectin/glycoprotein that maintains endoplasmic reticulum (ER) quality control and ER-associated degradation (the so-called ERAD pathway) of newly synthesized proteins. It is essential for the recognition of terminally misfolded non-glycosylated proteins and improperly folded glycoproteins, and binds to them to allow first their retention in the ER, and then second, subsequent transfer to the degradation machinery. The cation-selective channel TRPV4 is OS9's major target.
