High impact information on OST1

• Suppression of an ost1 mutation by overexpression of OST5 indicates that this small membrane protein directly interacts with other OTase components, most likely with Ost1p [1].
• Microsomal membranes isolated from the ost1 mutants contained elevated amounts of the Kar2 stress-response protein [2].
• Microsomal membranes isolated from ost1 mutant yeast showed marked reductions in the in vitro transfer of high mannose oligosaccharide from exogenous lipid-linked oligosaccharide to a glycosylation site acceptor tripeptide [2].
• A disruption of the OST1 locus was not tolerated in haploid yeast showing that expression of the Ost1 protein is essential for vegetative growth of yeast [2].
• The Saccharomyces cerevisiae oligosaccharyltransferase was purified as a heteroligomeric complex consisting of six subunits (alpha-zeta) having apparent molecular masses of 64 kD (Ost1p), 45 kD (Wbp1p), 34 kD, 30 kD (Swp1p), 16 kD, and 9 kD [3].

Biological context of OST1

• Four essential gene products, Ost1p, Wbp1p, Swp1p, and Stt3p were shown to be cross-linked to each other in a pairwise fashion [4].
• Deletion of the cytoplasmic tail of Ost1p caused no defects in growth and glycosylation [5].
• In contrast, a construct containing only the luminal domain of Ost1p did not support cell growth [5].
• By further mutagenesis of the conserved residues of Ost1p we conclude that the luminal domain mediates interactions with other subunits of OT and becomes labeled because of its proximity to the recognition andor catalytic subunit in the OT complex, Stt3p [5].
• Amino acid sequences from the 64 kDa glycoprotein subunit of the complex were used to clone the essential NLT1 (N-linked oligosaccharyl transferase) gene [6].

Anatomical context of OST1

• However, using microsomes prepared from these three strains, the labeling of Ost1p was markedly decreased upon photoactivation with the Asn-Bpa-Thr photoprobe [7].

Associations of OST1 with chemical compounds

• Studies on the function of oligosaccharyl transferase subunits: a glycosylatable photoprobe binds to the luminal domain of Ost1p [5].
• The Ost1p subunit of yeast oligosaccharyl transferase recognizes the peptide glycosylation site sequence, -Asn-X-Ser/Thr- [8].
• The essential yeast NLT1 gene encodes the 64 kDa glycoprotein subunit of the oligosaccharyl transferase [6].
• A yeast strain was created in which the essential 64-kDa glycoprotein Nlt1p subunit of the oligosaccharyl transferase was modified by the addition of a 22-residue carboxy-terminal affinity tag; the tag included both an 8-residue FLAG epitope and a 6-residue histidine motif [9].
• In the present study, we demonstrated that the abi1-1 mutation, but not the abi2-1 mutation, strongly inhibited ABA-dependent SRK2E/OST1 activation [10].

Other interactions of OST1

• Due to the challenges with purifying the active enzyme complex for detailed biophysical studies, a systematic study to express, isolate, and characterize the soluble domains of three of the largest subunits in the complex (Nlt1p, Wbp1p, and Swp1p) is reported [11].

Analytical, diagnostic and therapeutic context of OST1

• Protein sequence analysis revealed a significant sequence identity between the Saccharomyces cerevisiae Ost1 protein and ribophorin I, a previously identified subunit of the mammalian oligosaccharyltransferase [2].
• Using a combination of biochemical and genetic techniques the subunit Ost1p has been shown to recognize Asn-X-Ser/Thr glycosylation sites [12].

References