title: Amino acid and carbohydrate structural variants of glycoprotein products (M-N glycoproteins) of the M-N allelic locus.
abstract: Major glycoprotein of MgM, MM Miltenberger III (MiIII), and M-N erythrocyte membranes from individual donors were cleaved with CNBr and their amino-terminal octapeptides were examined with respect to amino acid and carbohydrate composition. The amino-terminal octapeptides from the heterozygous MgM donor were resolved into two types, A and A'. MgM A was identical to octapeptide A from MM glycoproteins in carbohydrate and amino acid compositions. MgM A' exhibited amino acid composition similar to NN peptide A except for a single substitution of an Asx for a Thr and, as a result, was not glycosylated. MM(MiIII) octapeptide A was identical to M peptide A in amino acid composition, but differed in carbohydrate content. This glycopeptide contained three O-glycosidically linked carbohydrate units, one of which contained GlcNAc bound to a core of NeuAc, Gal, and GalNAc. About two such units were also present in the CNBr glycopeptide B of the glycoprotein, and on the basis of studies with alkaline borohydride and alkaline sulfite degradations, these units are believed to have the following structure: (formula see text) The Mg is an allelomorph of the M-N locus, likely evolved from a single base substitution in the N gene. The resulting single amino acid substitution effects the posttranslational carbohydration of neighboring Ser and Thr residues. The MM(MiIII) appears to be a product of the M gene that undergoes sequences of posttranslational glycosylations different from those of the M-N glycoproteins.
mesh_terms: D000483:Alleles; D000596:Amino Acids / Q000032:analysis; D002241:Carbohydrates / Q000032:analysis; D003488:Cyanogen Bromide; D004912:Erythrocytes / Q000032:analysis; D014644:Genetic Variation; D006021:Glycophorins / Q000235:genetics*; D006801:Humans; D010446:Peptide Fragments / Q000032:analysis; D011110:Polymorphism, Genetic; D012795:Sialoglycoproteins / Q000235:genetics*
chemical_list: D000596:Amino Acids; D002241:Carbohydrates; D006021:Glycophorins; D010446:Peptide Fragments; D012795:Sialoglycoproteins; D003488:Cyanogen Bromide