8.A.67 The Os-9 Quality Control (ERAD) Protein (Os-9) Family

Os9 is a lectin which functions in endoplasmic reticulum (ER) quality control and ER-associated degradation (ERAD). May bind terminally misfolded non-glycosylated proteins as well as improperly folded glycoproteins, retain them in the ER, and transfer them to the ubiquitination machinery to promote their degradation. Probable transport protein targets include TRPV4.6 (TC# 1.A.4.2.5) (Wang et al. 2007) and KNCC2 (2.A.30.1.1) (Seaayfan et al. 2015).  The Os-9 protein of humans contains a PRKCSH domain which is similar to a region found in the beta-subunit of glucosidase II, which is also known as protein kinase C substrate 80K-H (PRKCSH). The beta subunit is required for the solubility and stability of the heterodimeric enzyme, and is involved in retaining the enzyme within the endoplasmic reticulum. Mutations in the gene coding for PRKCSH have been found to be involved in the development of autosomal dominant polycystic liver disease (ADPLD). This family also includes an ER sensor for misfolded glycoproteins and is therefore likely to be a generic sugar binding domain (25692846).

This family belongs to the .



D'Alessio, C. and N.M. Dahms. (2015). Glucosidase II and MRH-domain containing proteins in the secretory pathway. Curr. Protein. Pept. Sci. 16: 31-48.

Seaayfan, E., N. Defontaine, S. Demaretz, N. Zaarour, and K. Laghmani. (2015). OS9 interacts with NKCC2 and targets its immature form for the endoplasmic-reticulum-associated degradation pathway. J. Biol. Chem. [Epub: Ahead of Print]

Wang, Y., X. Fu, S. Gaiser, M. Köttgen, A. Kramer-Zucker, G. Walz, and T. Wegierski. (2007). OS-9 regulates the transit and polyubiquitination of TRPV4 in the endoplasmic reticulum. J. Biol. Chem. 282: 36561-36570.

Wu, X. and T.A. Rapoport. (2018). Mechanistic insights into ER-associated protein degradation. Curr. Opin. Cell Biol. 53: 22-28. [Epub: Ahead of Print]


TC#NameOrganismal TypeExample

The Os-9 quality control (ERAD) protein of 667 aas and 1 N-terminal TMS (Seaayfan et al. 2015).

Os-9 Protein of Homo sapiens


OS-9 homologue of 282 aas and 1 N-terminal TMS.

OS-9 of Arabidopsis thaliana (Mouse-ear cress)


Epididymis luminal protein 117 or ER lectin 1 or 483 aas and 1 N-terminal TMS (25692846).

ER lectin of Homo sapiens


Uncharacterized protein of 464 aas and 1- N-terminal TMS

UP of Ceriporiopsis subvermispora (White-rot fungus)


Yos9 or os9 protein of 542 aas and 1 N-terminal TMS. Functions in the ERAD pahway for unfolded protein export from the lumen of the ER to the cytoplasm where it is ubiquitinated and degraded in a proteosome (see TC# 3.A.16.1.2) (Wu and Rapoport 2018).

Yos9 of Saccharomyces cerevisiae (Baker's yeast)