Open AccessInitial glycosylation of proteins with acetylgalactosaminylserine linkages.
Author(s) -
Ger J. Strous
Publication year - 1979
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.76.6.2694
Subject(s) - threonine , biochemistry , glycosylation , chemistry , glycoprotein , serine , monosaccharide , endoplasmic reticulum , oligosaccharide , glycan , amino acid , mannose , enzyme
Epithelial glycoprotein like that produced by the gastric surface consists of a polypeptide chain rich in serine and threonine; to these amino acid residues oligosaccharide chains of variable length are linked. The linking sugar is acetylgalactosamine. To find out whether the initial glycosylation takes place at the ribosomal level. I treated purified peptidyl-tRNA, derived from rat gastric membrane-bound polysomes, with alkali in the presence of boro[3H]hydride. Alkali specifically splits glycosidic bonds between serine or threonine and oligosaccharide side chains (beta-elimination reaction). The linking sugar is converted to an alditol and simultaneously labeled. GalNAc was identified as the linking sugar by paper chromatography. Furthermore, nascent peptides with lengths between 40 and 60 amino acid residues already contained this linking sugar. Gel filtration on Bio-Gel P-2 of 3H-labeled saccharides revealed that nascent chains contained mainly monosaccharides, but some di- or trisaccharides were found with GalNAc as the linkage sugar. These findings demonstrate that initial glycosylation of epithelial glycoprotein occurs at the ribosomal level rather shortly after the nascent peptide chain has reached the cisternal lumen of the endoplasmic reticulum.