title: Coordination of N-glycosylation and protein translocation across the endoplasmic reticulum membrane by Sss1 protein.
abstract: Secretory proteins are translocated across the endoplasmic reticulum (ER) membrane through a channel formed by three proteins, namely Sec61p, Sbh1p, and Sss1p (Johnson, A. E., and van Waes, M. A. (1999) Annu. Rev. Cell Dev. Biol. 15, 799-842). Sec61p and Sss1p are essential for translocation (Esnault, Y., Blondel, M. O., Deshaies, R. J., Schekman, R., and Kepes, F. (1993) EMBO J. 12, 4083-4093). Sec61p is a polytopic membrane protein that lines the protein translocation channel. The role of Sss1p is unknown. During import into the ER through the Sec61p channel, many proteins are N-glycosylated before translocation is completed. In addition, both the Sec61 channel and oligosaccharyl transferase (OST) copurify with ribosomes from rough ER, suggesting that OST is located in close proximity to the Sec61 channel (Gorlich, D., Prehn, S., Hartmann, E., Kalies, K.-U., and Rapoport, T. A. (1992) Cell 71, 489-503 and Wang, L., and Dobberstein, B. (1999) FEBS Lett. 457, 316-322). Here, we demonstrate a direct interaction between Sss1p and a subunit of OST, Wbp1p, using the split-ubiquitin system and co-immunoprecipitation. We generated mutants in the cytoplasmic domain of Sss1p that disturb the interaction with OST and are viable but display a translocation defect specific for proteins with glycosylation acceptor sites. Our data suggest that Sss1p coordinates translocation across the ER membrane and N-linked glycosylation of secretory proteins.
authors.affiliation: University of Cambridge, Cambridge Institute for Medical Research, Hills Road, Cambridge CB2 2XY, United Kingdom.
authors.forename: Wiep
authors.initials: W
authors.lastname: Scheper
authors.forename: Safia
authors.initials: S
authors.lastname: Thaminy
authors.forename: Sanja
authors.initials: S
authors.lastname: Kais
authors.forename: Igor
authors.initials: I
authors.lastname: Stagljar
authors.forename: Karin
authors.initials: K
authors.lastname: Römisch
mesh_terms: D000595:Amino Acid Sequence; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology*; D006023:Glycoproteins / Q000378:metabolism*; D006031:Glycosylation; D006602:Hexosyltransferases; D008565:Membrane Proteins / Q000737:chemistry* / Q000502:physiology*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D021381:Protein Transport; D000069816:SEC Translocation Channels; D029701:Saccharomyces cerevisiae Proteins; D013329:Structure-Activity Relationship; D014166:Transferases / Q000502:physiology
chemical_list: D005656:Fungal Proteins; D006023:Glycoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C084005:SSS1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014166:Transferases; D006602:Hexosyltransferases; C025620:dolichyl-diphosphooligosaccharide - protein glycotransferase