Specificity of anti-Mg antibody--a study with synthetic peptides and glycopeptides

The specificity of a human anti-Mg antibody has been evaluated by agglutination-inhibition assays using several peptides and glycopeptides structurally related to the N-terminal end of glycophorin A, which were obtained by chemical synthesis. We have shown that the anti-Mg antibody is strongly inhibited by pentapeptides containing a leucine residue at their N-terminal end. Glycosylations of these peptides at positions 2, 3 and 4 by N-acetylgalactosamine and/or galactose-beta 1-3-N-acetylgalactosamine units abolish the biological activity, as well as the masking of the leucine residue by addition of N-acetylglycine. The results demonstrate also that the presence of an asparagine residue at position 4 of the pentapeptides (or glycopeptides) is not a requirement for Mg specificity and suggest that the antibody recognizes primarily a nonglycosylated peptide structure with an N-terminal leucine residue.