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. OS9 forms part of the HRD1 ubiquitin ligase complex (SYVN1/HRD1 and SEL1L) which is involved in the retro-translocation of misfolded proteins from the ER to cytosol for ubiquitin-dependent degradation. OS9 has been shown to specifically protect some proteins from this process before maturation, ensuring biological functionality.
Immunocytochemistry/Immunofluorescence: OS9 Antibody [
A Swiss group used an OS9 antibody for immunoprecipitation, western blotting, and immunofluorescence studies aimed at understanding the role of OS09 variants in mammalian ER quality control with respect to both retention and disposal1. Huang’s group from Taiwan examined Derlin1 and Derlin2 proteins through immunoblotting with the OS9 antibody to monitor ERAD complex formation and substrate binding2. Based on their studies, it appears that in mammalian systems, unlike those of yeast, the ERAD system requires multiple derlin proteins that each pair to function with a particular partner protein. Very recently, Angela Schipanksi et al used an OS9 antibody to discover that OS9 delivers mutant neuroserpin to the ER in encephalopathy 3.
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