The essential OST2 gene encodes the 16-kD subunit of the yeast oligosaccharyltransferase, a highly conserved protein expressed in diverse eukaryotic organisms
UMass Chan AffiliationsDepartment of Biochemistry and Molecular Biology
KeywordsAmino Acid Sequence
Molecular Sequence Data
MetadataShow full item record
AbstractOligosaccharyltransferase 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 non-identical subunits (alpha-zeta). The alpha, beta, gamma, and delta subunits of the oligosaccharyltransferase are encoded by the OST1, WBP1, OST3, and SWP1 genes, respectively. Here we describe the functional characterization of the OST2 gene that encodes the epsilon-subunit of the oligosaccharyltransferase. Genomic disruption of the OST2 locus was lethal in haploid yeast showing that expression of the Ost2 protein is essential for viability. Overexpression of the Ost2 protein suppresses the temperature-sensitive phenotype of the wbp1-2 allele and increases in vivo and in vitro oligosaccharyltransferase activity in a wbp1-2 strain. An analysis of a series of conditional ost2 mutants demonstrated that defects in the Ost2 protein cause pleiotropic underglycosylation of soluble and membrane-bound glycoproteins. Microsomal membranes isolated from ost2 mutant yeast show marked reductions in the in vitro transfer of high mannose oligosaccharide from exogenous lipid-linked oligosaccharide to a glycosylation site acceptor tripeptide. Surprisingly, the Ost2 protein was found to be 40% identical to the DAD1 protein (defender against apoptotic cell death), a highly conserved protein initially identified in vertebrate organisms. The protein sequence of ost2 mutant alleles revealed mutations at highly conserved residues in the Ost2p/DAD1 protein sequence.
SourceJ Cell Biol. 1995 Oct;131(2):371-83.
Permanent Link to this Itemhttp://hdl.handle.net/20.500.14038/42614
Related ResourcesLink to Article in PubMed
Showing items related by title, author, creator and subject.
The unique catalytic subunit of sperm cAMP-dependent protein kinase is the product of an alternative Calpha mRNA expressed specifically in spermatogenic cellsSan Agustin, Jovenal T.; Wilkerson, Curtis G.; Witman, George B. (2000-09-12)cAMP-dependent protein kinase has a central role in the control of mammalian sperm capacitation and motility. Previous protein biochemical studies indicated that the only cAMP-dependent protein kinase catalytic subunit (C) in ovine sperm is an unusual isoform, termed C(s), whose amino terminus differs from those of published C isoforms of other species. Isolation and sequencing of cDNA clones encoding ovine C(s) and Calpha1 (the predominant somatic isoform) now reveal that C(s) is the product of an alternative transcript of the Calpha gene. C(s) cDNA clones from murine and human testes also were isolated and sequenced, indicating that C(s) is of ancient origin and widespread in mammals. In the mouse, C(s) transcripts were detected only in testis and not in any other tissue examined, including ciliated tissues and ovaries. Finally, immunohistochemistry of the testis shows that C(s) first appears in pachytene spermatocytes. This is the first demonstration of a cell type-specific expression for any C isoform. The conservation of C(s) throughout mammalian evolution suggests that the unique structure of C(s) is important in the subunit's localization or function within the sperm.
The 78,000 M(r) intermediate chain of Chlamydomonas outer arm dynein isa WD-repeat protein required for arm assemblyWilkerson, Curtis G.; King, Stephen M.; Koutoulis, Anthony; Pazour, Gregory J.; Witman, George B. (1995-04-01)We have isolated and sequenced a full-length cDNA clone encoding the 78,000 Mr intermediate chain (IC78) of the Chlamydomonas outer arm dynein. This protein previously was shown to be located at the base of the solubilized dynein particle and to interact with alpha tubulin in situ, suggesting that it may be involved in binding the outer arm to the doublet microtubule. The sequence predicts a polypeptide of 683 amino acids having a mass of 76.5 kD. Sequence comparison indicates that IC78 is homologous to the 69,000 M(r) intermediate chain (IC69) of Chlamydomonas outer arm dynein and to the 74,000 M(r) intermediate chain (IC74) of cytoplasmic dynein. The similarity between the chains is greatest in their COOH-terminal halves; the NH(2)-terminal halves are highly divergent. The COOH-terminal half of IC78 contains six short imperfect repeats, termed WD repeats, that are thought to be involved in protein-protein interactions. Although not previously reported, these repeated elements also are present in IC69 and IC74. Using the IC78 cDNA as a probe, we screened a group of slow-swimming insertional mutants and identified one which has a large insertion in the IC78 gene and seven in which the IC78 gene is completely deleted. Electron microscopy of three of these IC78 mutants revealed that each is missing the outer arm, indicating that IC78 is essential for arm assembly or attachment to the outer doublet. Restriction fragment length polymorphism mapping places the IC78 gene on the left arm of chromosome XII/XIII, at or near the mutation oda9, which also causes loss of the outer arm. Mutants with defects in the IC78 gene do not complement the oda9 mutation in stable diploids, strongly suggesting that ODA9 is the structural gene for IC78.
Interspecies conservation of outer arm dynein intermediate chain sequences defines two intermediate chain subclassesOgawa, Kazuo; Kamiya, Ritsu; Wilkerson, Curtis G.; Witman, George B. (1995-06-01)Immunological analysis showed that antibodies against the intermediate chains (ICs) IC2 and IC3 of sea urchin outer arm dynein specifically cross-reacted with intermediate chains IC78 and IC69, respectively, of Chlamydomonas outer arm dynein. In contrast, no specific cross-reactivity with any Chlamydomonas outer arm polypeptide was observed using antibody against IC1 of sea urchin outer arm dynein. To learn more about the relationships between the different ICs, overlapping cDNAs encoding all of IC2 and IC3 of sea urchin were isolated and sequenced. Comparison of these sequences with those previously obtained for the Chlamydomonas ICs revealed that, although all four chains are homologous, sea urchin IC2 is much more closely related to Chlamydomonas IC78 (45.8% identity), and sea urchin IC3 is much more closely related to Chlamydomonas IC69 (48.5% identity), than either sea urchin chain is related to the other (23.5% identity). For homologous pairs, the similarities extend throughout the full lengths of the chains. Regions of similarity between all four ICs and the IC (IC74) of cytoplasmic dynein, located in the C-terminal halves of the chains, are due primarily to conservation of the WD repeats present in all of these ICs. This is the first demonstration that structural differences between individual ICs within an outer arm dynein have been highly conserved in the dyneins of distantly related species. The results provide a basis for the subclassification of these chains.