Unmasking a new recognition signal for O-linked glycosylation in the chorionic gonadotropin beta subunit.
hCGbeta subunit is distinguished among the other members of the family of the glycoprotein hormones by the presence of four serine O-linked oligosaccharide units in the last 25 amino acids. This carboxy terminal peptide (CTP) influences the intracellular behavior of the subunit and is important for maintaining the biological half-life of hCG. To examine how the O-linked oligosaccharides affect the metabolic behavior of hCG, we generated a CGbeta mutant devoid of the native O-linked acceptor sites. An alternative site not used in the native subunit was glycosylated and the structure of this oligosaccharide differed from the wild-type O-linked carbohydrates. This glycosylation occurred at serine 130 in the CTP and in contrast to the wild type O-linked oligosaccharides, sialic acid is a major component of the alternatively linked carbohydrate. The data show that deleting the native acceptor sites exposes a new site for O-glycosylation and promotes a differential intracellular processing of the beta subunit. These results support the hypothesis that the CTP participates in the folding of the newly synthesized subunit, which is manifested by the post-translational changes reported here.
Garcia-Campayo
Vicenta
V
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
Sugahara
Tadashi
T
Boime
Irving
I
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D016466:CHO Cells; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D006224:Cricetinae; D006031:Glycosylation; D006801:Humans; D009154:Mutation; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D011974:Receptors, LH / Q000378:metabolism; D012694:Serine; D014162:Transfection
D018997:Chorionic Gonadotropin, beta Subunit, Human; D011974:Receptors, LH; D012694:Serine