title: Identification of two distinct intracellular localization signals in STT3-B.
abstract: The STT3 subunit of the oligosaccharyltransferase complex plays a critical role in the N-glycosylation process. From Arabidopsis thaliana to Homo sapiens, two functional STT3 isoforms have been identified, STT3-A and STT3-B. We report that the last transmembrane (TM) segment of STT3-B corresponds to a topogenic determinant that is sufficient for proper integration and orientation of STT3-B C-terminal domain. Notably, the last TM segment of STT3-A and -B isoforms present major differences in amino acid sequence and predicted 3D structure. We also identified a bipartite nuclear targeting sequence in the C-terminal tail of STT3-B that is absent in STT3-A. The latter sequence is sufficient to induce nucleolar localization of a reporter protein. Our results show that STT3-A and -B display two structural differences that may have a drastic influence on their function and might account for the remarkable evolutionary conservation of the two STT3 paralogs.
authors.affiliation: Institute of Research in Immunology and Cancer, University of Montreal, CP 6128, Downtown Station, Montreal, Que., Canada H3C 3J7.
authors.forename: Etienne
authors.initials: E
authors.lastname: Caron
authors.forename: Caroline
authors.initials: C
authors.lastname: Côté
authors.forename: Marc
authors.initials: M
authors.lastname: Parisien
authors.forename: François
authors.initials: F
authors.lastname: Major
authors.forename: Claude
authors.initials: C
authors.lastname: Perreault
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002522:Chlorocebus aethiops; D019295:Computational Biology; D017124:Conserved Sequence; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D007527:Isoenzymes; D008565:Membrane Proteins; D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; C502741:STT3-A protein, mouse