HGNC Approved Gene Symbol: OST4
Cytogenetic location: 2p23.3 Genomic coordinates (GRCh38): 2:27,070,472-27,071,654 (from NCBI)
OST4 is a noncatalytic subunit of membrane-associated oligosaccharyltransferase (OST) complexes, which catalyze N-glycosylation of nascent polypeptides in the endoplasmic reticulum (ER) lumen (Dumax-Vorzet et al., 2013).
Dumax-Vorzet et al. (2013) reported that human OST4 contains 37 amino acids, including a central transmembrane (TM) domain and a putative C-terminal ER localization motif. OST4 orthologs are present in diverse eukaryotes, and vertebrate OST4 orthologs share 94% amino acid identity. C-terminal FLAG-tagged human OST4 localized to the ER of transfected COS-7 cells.
Gross (2020) mapped the OST4 gene to chromosome 2p23.3 based on an alignment of the OST4 sequence (GenBank NM_001134693) with the genomic sequence (GRCh38).
Using NMR spectroscopy, Gayen and Kang (2011) determined the solution structure of human OST4. OST4 contains a flexible N terminus (residues 1 to 4) and C terminus (residues 31 to 37). Between the N and C termini is an alpha-helical structure (residues 5 to 30) containing a single TM domain with a kink.
Dumax-Vorzet et al. (2013) found that human OST4 assembled into distinct OST complexes through association with STT3A (601134) or STT3B (608605), as well as with the OST accessory subunit, ribophorin I (RPN1; 180470). Mutation analysis showed that association of OST4 with these core OST subunits depended on its TM domain. Knockdown experiments showed that OST4 preferentially stabilized STT3A and its interacting partner, KCP2 (KRTCAP2; 619023). STT3A and/or ribophorin I, in turn, stabilized OST4 in the complex. Depletion of OST4 destabilized both STT3A- and STT3B-containing OST complexes and released a ribophorin I-containing subcomplex. OST4 and ribophorin I stabilized whole OST complexes, and both proteins modulated the efficiency of N-glycosylation of endogenous prosaposin (PSAP; 176801) in HeLa cells.
Dumax-Vorzet, A., Roboti, P., High, S. OST4 is a subunit of the mammalian oligosaccharyltransferase required for efficient N-glycosylation. J. Cell Sci. 126: 2595-2606, 2013. [PubMed: 23606741] [Full Text: https://doi.org/10.1242/jcs.115410]
Gayen, S., Kang, C. Solution structure of a human minimembrane protein Ost4, a subunit of the oligosaccharyltransferase complex. Biochem. Biophys. Res. Commun. 409: 572-576, 2011. [PubMed: 21609714] [Full Text: https://doi.org/10.1016/j.bbrc.2011.05.050]
Gross, M. B. Personal Communication. Baltimore, Md. 6/29/2020.