Eukaryotic N-glycosylation is catalysed in the ER lumen, where the enzyme oligosaccharyltransferase (OTase) transfers donor glycans from a dolichol pyrophosphate (DolP) carrier (Lipid-linked oligosaccharide; LLO) to polypeptides. The yeast OTase is a hetero-oligomeric complex composed of essential (Ost1, Ost2, Wbp1, Stt3, and Swp1) and nonessential (Ost3, Ost4, Ost5, and Ost6) subunits. This domain family is found in Ost5, Swiss:Q92316. The precise function of this subunit is not known, however Ost5 appears to form a sub-complex with Ost1, and this sub-complex associates with the catalytic Stt3 subunit of OTase. Down regulation of Ost5 resulted in a limited effect on glycosylation and no effect on the stability of Ost1 or Stt3 subunits [1, 2].

1: SWATH-MS Glycoproteomics Reveals Consequences of Defects in the Glycosylation Machinery. Zacchi LF, Schulz BL; Mol Cell Proteomics. 2016;15:2435-2447. PMID:27094473

2: A specific screen for oligosaccharyltransferase mutations identifies the 9 kDa OST5 protein required for optimal activity in vivo and in vitro. Reiss G, te Heesen S, Gilmore R, Zufferey R, Aebi M; EMBO J. 1997;16:1164-1172. PMID:9135133