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OST4 is a subunit of the mammalian oligosaccharyltransferase required for efficient N-glycosylation.

Journal of cell science | Jun 15, 2013

The eukaryotic oligosaccharyltransferase (OST) is a membrane-embedded protein complex that catalyses the N-glycosylation of nascent polypeptides in the lumen of the endoplasmic reticulum (ER), a highly conserved biosynthetic process that enriches protein structure and function. All OSTs contain a homologue of the catalytic STT3 subunit, although in many cases this is assembled with several additional components that influence function. In S. cerevisiae, one such component is Ost4p, an extremely small membrane protein that appears to stabilise interactions between subunits of assembled OST complexes. OST4 has been identified as a putative human homologue, but to date neither its relationship to the OST complex, nor its role in protein N-glycosylation, have been directly addressed. Here, we establish that OST4 is assembled into native OST complexes containing either the catalytic STT3A or STT3B isoforms. Co-immunoprecipitation studies suggest that OST4 associates with both STT3 isoforms and with ribophorin I, an accessory subunit of mammalian OSTs. These presumptive interactions are perturbed by a single amino acid change in the transmembrane region of OST4. Using siRNA knockdowns and native gel analysis, we show that OST4 plays an important role in maintaining the stability of native OST complexes. Hence, upon OST4 depletion well-defined OST complexes are partially destabilised and a novel ribophorin I-containing subcomplex can be detected. Strikingly, cells depleted of either OST4 or STT3A show a remarkably similar defect in the N-glycosylation of endogenous prosaposin. We conclude that OST4 most likely promotes co-translational N-glycosylation by stabilising STT3A-containing OST isoforms.

Pubmed ID: 23606741 RIS Download

Mesh terms: Amino Acid Sequence | Animals | COS Cells | Cell Line | Cell Line, Tumor | Cercopithecus aethiops | Endoplasmic Reticulum | Glycosylation | HeLa Cells | Hep G2 Cells | Hexosyltransferases | Humans | Mammals | Membrane Proteins | Molecular Sequence Data | Protein Subunits | Saposins | Sequence Alignment

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Associated grants

  • Agency: Wellcome Trust, Id: 081671/B/06/Z
  • Agency: Biotechnology and Biological Sciences Research Council, Id: BB/G000948/1

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Tool to align three or more sequences together in a computationally efficient manner. This multiple sequence alignment program for DNA or proteins attempts to calculate the best match for the selected sequences, and lines them up so that the identities, similarities and differences can be seen. Evolutionary relationships can be seen via viewing Cladograms or Phylograms. The alignment is progressive and considers sequence redundancy. SOAP Web services are also available. Note: ClustalW2 is no longer being maintained. Please consider using the new version instead: Clustal Omega, http://www.ebi.ac.uk/Tools/msa/clustalo/ There are two ways to use this service at the EBI. The first is interactively (default) and the second is by email. Using it interactively, the user must wait for the results to be displayed in the browser window. The email option means that the results will not be displayed in the browser window but will be sent by email. The email option is the better one to take when submitting large amounts of data. The program accepts nucleic acid or protein sequences, in the following multiple sequence formats: NBRF/PIR, EMBL/UniProt, Pearson (FASTA), GDE, ALN/ClustalW, GCG/MSF, RSF. Note: ClustalW2 is no longer being maintained. Please consider using the new version instead: Clustal Omega

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