The essential OST2 gene encodes the 16-kD subunit of the yeast oligosaccharyltransferase, a highly conserved protein expressed in diverse eukaryotic organisms.

Abstract

Abstract. Oligosaccharyltransferase catalyzes the transfer of a preassembled high mannose oligosaccharide from a dolichol-oligosaccharide donor to consensus glycosylation acceptor sites in newly synthesized proteins in the lumen of the rough endoplasmic reticulum. The Saccharomyces cerevisiae oligosaccharyltransferase is an oligomeric complex composed of six nonidentical subunits (c~-~). The a, [3, y, and 8 PARAGINE-linked glycosylation of proteins is a highly conserved protein modification reaction that occurs in the lumen of the rough endoplasmic reticulum in all eukaryotic organisms (Kornfeld and Kornfeld, 1985;Herscovics and Orlean, 1993). The initial stage in the biosynthesis of N-glycosylated proteins, catalyzed by the lumenally oriented enzyme oligosaccharyltransferase, involves the transfer of a preassembled high-mannose oligosaccharide (Glc3Man9GlcNAc2) from a dolichol-pyrophosphate donor onto asparagine acceptor sites within the consensus sequon Asn-X-Ser/Thr, where X can be any amino acid except proline (Gavel and Von Heijne, 1990). N-linked glycosylation is an obligatory event for the efficient folding and oligomeric assembly of many nascent

The highly conserved DAD1 protein involved in apoptosis is required for N‐linked glycosylation

“…A few yellow spots suggested that some DAD1 were colocalized with the Golgi apparatus. Taking these results together, we concluded that DAD1 proteins are mostly localized in the ER, consistent with the previous report that the yeast homologue Ost2p is present in the ER (Silberstein et al 1995).…”

“…However, OST2 did not confer the ts + phenotype to tsBN7 cells. Since Ost2p functions as a part of the six subunits of the yeast oligosaccharyltransferase complex and is not considered to be the catalytic domain (Silberstein et al 1995), Ost2p alone may not be able to give proper enzymatic activity in mammalian cells. The attempt to complement the yeast ost2 defect with the human DAD1 or other plant homologues has so far been unsuccessful (Dr R. Gilmore, University of Massachusetts, personal communication).…”

“…Recently, DAD1 has been reported to be highly homologus to Ost2p, a subunit of S. cerevisiae oligosaccharyltransferase (Silberstein et al 1995). In order to address the question as to whether or not Ost2p and DAD1 share the same function, we examined whether the N-linked glycosylation was affected in tsBN7 cells upon a shift to the restrictive temperature, 39.5 ЊC, at which temperature DAD1 is lost in tsBN7 cells due to mutation (Nakashima et al 1993).…”

“…Genes encoding five of them have been identified as OST1, WBP1, OST3, SWP1 and OST2. Defects in each of them cause a marked reduction in N-linked glycosylation, and four of them: OST1, WBP1, SWP1 and OST2, are essential for survival (Silberstein et al 1995), as is DAD1. Consistent with their structural similarity, we found that a loss of DAD1 function caused defects in N-linked glycosylation in hamster tsBN7 cells.…”

Abnormalities of developmental cell death in Dad1‐deficient mice

“…Indeed, homologues of Dad1 were isolated from many eukaryotic organisms and proved to be highly homologous to each other. Even with the yeast homologue Ost2p, amino acid sequences are 40% identical and 65% similar to those of human DAD1 (Silberstein et al 1995). Although the temperature-sensitive apoptosis of tsBN7 cannot be prevented by yeast OST2 cDNA, it can be prevented by Xenopus, C. elegans, Arabidopsis thaliana and rice, in addition to human DAD1 (Sugimoto et al 1995;Gallois et al 1997;Makishima et al 1997;Tanaka et al 1997a;Nakashima et al 1993).…”