title: Glycosylation efficiency of Asn-Xaa-Thr sequons depends both on the distance from the C terminus and on the presence of a downstream transmembrane segment.
abstract: Statistical studies of N-glycosylated proteins have indicated that the frequency of nonglycosylated Asn-Xaa-(Thr/Ser) sequons increases toward the C terminus (Gavel, Y., and von Heijne, G. (1990) Protein Eng. 3, 433-442). Using in vitro transcription/translation of a truncated model protein in the presence of dog pancreas microsomes, we find that glycosylation efficiency of Asn-Xaa-Thr sequons indeed is reduced when the sequon is within approximately 60 residues of the C terminus. Surprisingly, the presence of a hydrophobic stop transfer sequence between the Asn-Xaa-Thr sequon and the C terminus results in a very different dependence of glycosylation efficiency on the distance to the C terminus, where the presence of the stop transfer segment inside the ribosome appears to cause a drastic drop in the level of glycosylation. We speculate that this may reflect a change in the structure of the ribosome/translocon complex induced by the stop transfer segment.
authors.affiliation: Department of Biochemistry, Stockholm University, S-106 91 Stockholm, Sweden.
authors.forename: I
authors.initials: I
authors.lastname: Nilsson
authors.forename: G
authors.initials: G
authors.lastname: von Heijne
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D004285:Dogs; D004926:Escherichia coli / Q000201:enzymology; D006023:Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D006031:Glycosylation; D008565:Membrane Proteins; D008861:Microsomes / Q000378:metabolism; D008958:Models, Molecular; D010179:Pancreas / Q000378:metabolism; D014176:Protein Biosynthesis; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013912:Threonine; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D006023:Glycoproteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; D013912:Threonine; D001216:Asparagine; D012697:Serine Endopeptidases; C026515:type I signal peptidase