SV40 large T antigen is modified with O-linked N-acetylglucosamine but not with other forms of glycosylation.
SV40 large T antigen has been reported to be modified with several different sugars including N-acetylglucosamine, galactose, and mannose. In this report we have reexamined the glycosylation of T antigen and found that while we could detect modification with N-acetylglucosamine, we could not detect any other sugars on the protein. Surprisingly, even though [3H]galactose could be metabolically incorporated into the protein, analysis showed that all of the radioactivity in T antigen had been converted to other species. The N-acetylglucosamine was demonstrated to be linked to the protein in the form of O-linked N-acetylglucosamine, the best characterized form of nuclear and cytoplasmic glycosylation in mammalian systems. We have localized the major site of glycosylation to the amino terminal portion of the molecule. Analysis of mutated T antigen where serines 111/112 were substituted with alanine suggest that these residues constitute a glycosylation site on the protein. These two serines fall within a typical O-linked N-acetylglucosamine glycosylation site (PSS) and are also known to be phosphorylated. Thus, it is likely that competition between phosphorylation and glycosylation occurs at this site.
Medina
L
L
Department of Biochemistry and Cell Biology, Institute for Cell and Developmental Biology, State University of New York at Stony Brook, Stony Brook, NY 11794-5215, USA.
Grove
K
K
Haltiwanger
R S
RS
D000117:Acetylglucosamine / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000737:chemistry; D002460:Cell Line; D006031:Glycosylation; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010766:Phosphorylation
D000952:Antigens, Polyomavirus Transforming; D002241:Carbohydrates; D000117:Acetylglucosamine