BLOOD-GROUP MN-DEPENDENT DIFFERENCE IN DEGREE OF GALACTOSYLATION OF O-GLYCANS OF GLYCOPHORIN-A IS RESTRICTED TO THE GA1NAC RESIDUES LOCATEDON AMINO-ACID-RESIDUES-2-4 OF THE GLYCOPHORIN POLYPEPTIDE-CHAIN

Glycophorin A (GPA) of human erythrocytes contains a minor number of u nsubstituted GalNAc residues (Tn receptors) which are recognized by Mo luccella laevis lectin (MLL). The lectin reacts better with blood grou p N- than M-type of GPA which suggest a higher number of Tn receptors in GPA-N than in GPA-M, To find out whether this difference is restric ted to a defined domain of GPA, the N-terminal tryptic glycopeptides o f GPA-M and GPA-N (a,a, residues 1-39) and their fragments obtained by degradation with CNBr (a.a. residues 1-8 and 9-39) were analyzed. The untreated and desialylated glycopeptides were tested as inhibitors of MLL in ELISA, and the content of GalNAc-ol was determined in the prod ucts of beta-elimination of the asialoglycopeptides by gas-liquid chro matography/mass spectrometry. Tile asialoglycopeptides 1-39 and 1-8 de rived from GPA-N showed about 2 and 4 times higher content of non-gala ctosylated GalNAc residues, respectively, and higher reactivity with M LL than their counterparts derived from GPA-M, while asialoglycopeptid es 9-39 of GPA-M and GPA-N did not show such differences, These result s demonstrate that higher expression of non-galactosylated GalNAc in G PA-N than in GPA-M is confined to GalNAc residues located in the amino -terminal portion of GPA polypeptide chain, between the blood group M- and N-specific amino acid residues 1 and 5. (C) 1997 Federation of Eu ropean Biochemical Societies.