title: Size polymorphisms due to changes in the number of O-glycosylated tandem repeats in the Dictyostelium discoideum glycoprotein PsA.
abstract: The molecular weight polymorphism in the Dictyostelium discoideum cell surface glycoprotein PsA is due to incremental copies of an O-glycosylated tandem tetrapeptide repeat. Allelic variation at the pspA locus results in a PsA glycoprotein with three, four or five tandem copies of Pro-Thr-Val-Thr. The simplest explanation for the origin of this polymorphism is an unequal crossing over event in the ancestral gene containing four copies. Each Thr in the tandem repeat is substituted with carbohydrate, which is completely absent from PsA in strains carrying a glycosylation defective modB mutation. Glycosylated tandem repeats appear to be a common feature of cell surface glycoproteins which are characterized by short domains rich in Pro and Thr or Ser. It is probable that the glycosylated repeat domain acts as a "spacer" peptide that projects the globular domain above the glycocalyx.
authors.affiliation: School of Biological Sciences, Macquarie University, Sydney, New South Wales, Australia.
authors.forename: A A
authors.initials: AA
authors.lastname: Gooley
authors.forename: R
authors.initials: R
authors.lastname: Marshchalek
authors.forename: K L
authors.initials: KL
authors.lastname: Williams
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan; D004023:Dictyostelium / Q000235:genetics*; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics; D014644:Genetic Variation; D006031:Glycosylation; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation / Q000235:genetics; D011110:Polymorphism, Genetic / Q000235:genetics*; D015800:Protozoan Proteins; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*
chemical_list: D000953:Antigens, Protozoan; D005656:Fungal Proteins; D008562:Membrane Glycoproteins; D015800:Protozoan Proteins; C074496:prespore-specific antigen, Dictyostelium discoideum