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Gene Review

OST3  -  Ost3p

Saccharomyces cerevisiae S288c

Synonyms: Dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit 3, Oligosaccharyl transferase 34 kDa subunit, Oligosaccharyl transferase subunit OST3, Oligosaccharyl transferase subunit gamma, YOR085W, ...
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High impact information on OST3

  • Here we show that genomes of most multicellular eukaryotes encode two homologs of Stt3p and mammals express two homologs of Ost3p [1].
  • Compared to the previously characterized ost1-1 mutant in the oligosaccharyltransferase, and the alg5 mutant in the oligosaccharide assembly pathway, ost3 null mutant yeast appear to be selectively impaired in the glycosylation of several membrane glycoproteins [2].
  • Nonetheless, detergent extracts prepared from ost3 null mutant membranes are twofold less active than extracts prepared from wild-type membranes in an in vitro oligosaccharyltransferase assay [2].
  • We found that Ost2p and Stt3p have only their N terminus located in the cytosol, whereas Ost3p and Swp1p have only their C terminus oriented in the cytosol [3].
  • The residues critical for the OT activity and the stability of Stt3p-Ost4p-Ost3p subcomplex are located in helix alpha2, the larger cytosolic half of this kinked helix [4].

Biological context of OST3

  • Disruption of OST6 or OST3 causes only a minor defect in N-glycosylation, but an Deltaost3Deltaost6 double mutant displays a synthetic phenotype, leading to a severe underglycosylation of soluble and membrane-bound glycoproteins in vivo and to a reduced OST activity in vitro [5].

Anatomical context of OST3

  • These findings suggest that a localized region of the putative transmembrane domain of Ost4p mediates in stabilization of the interaction with the two other OT subunits (Ost3p and Stt3p) in a subcomplex in the endoplasmic reticulum membrane [6].

Associations of OST3 with chemical compounds

  • By blue native polyacrylamide electrophoresis we show that yeast OST consists of two isoforms with distinct functions differing only in the presence of the two related Ost3 and Ost6p proteins [7].

Other interactions of OST3

  • In this study we report the identification and functional characterization of a new OST gene, designated OST6, that has homology to OST3 and in particular a strikingly similar membrane topology [5].
  • The highly conserved Stt3 protein is a subunit of the yeast oligosaccharyltransferase and forms a subcomplex with Ost3p and Ost4p [8].

Analytical, diagnostic and therapeutic context of OST3


  1. Oligosaccharyltransferase isoforms that contain different catalytic STT3 subunits have distinct enzymatic properties. Kelleher, D.J., Karaoglu, D., Mandon, E.C., Gilmore, R. Mol. Cell (2003) [Pubmed]
  2. Functional characterization of Ost3p. Loss of the 34-kD subunit of the Saccharomyces cerevisiae oligosaccharyltransferase results in biased underglycosylation of acceptor substrates. Karaoglu, D., Kelleher, D.J., Gilmore, R. J. Cell Biol. (1995) [Pubmed]
  3. Studies of yeast oligosaccharyl transferase subunits using the split-ubiquitin system: topological features and in vivo interactions. Yan, A., Wu, E., Lennarz, W.J. Proc. Natl. Acad. Sci. U.S.A. (2005) [Pubmed]
  4. Structural basis for the function of a minimembrane protein subunit of yeast oligosaccharyltransferase. Zubkov, S., Lennarz, W.J., Mohanty, S. Proc. Natl. Acad. Sci. U.S.A. (2004) [Pubmed]
  5. The oligosaccharyltransferase complex from Saccharomyces cerevisiae. Isolation of the OST6 gene, its synthetic interaction with OST3, and analysis of the native complex. Knauer, R., Lehle, L. J. Biol. Chem. (1999) [Pubmed]
  6. Studies on the role of the hydrophobic domain of Ost4p in interactions with other subunits of yeast oligosaccharyl transferase. Kim, H., Park, H., Montalvo, L., Lennarz, W.J. Proc. Natl. Acad. Sci. U.S.A. (2000) [Pubmed]
  7. Yeast oligosaccharyltransferase consists of two functionally distinct sub-complexes, specified by either the Ost3p or Ost6p subunit. Schwarz, M., Knauer, R., Lehle, L. FEBS Lett. (2005) [Pubmed]
  8. The highly conserved Stt3 protein is a subunit of the yeast oligosaccharyltransferase and forms a subcomplex with Ost3p and Ost4p. Karaoglu, D., Kelleher, D.J., Gilmore, R. J. Biol. Chem. (1997) [Pubmed]
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