Structural Analysis of Glycophorin A from Miltenberger Class VIII Erythrocytes

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Abstract
The major human erythrocyte membrane sialoglycoprotein (glycophorin A or MN glycoprotein) was purified from the erythrocytes of two individuals heterozygous for the Mi-VIII gene in the Miltenberger subsystem of the MNSs blood-group system. The complete structure of a tryptic glycopeptide from glycophorin A comprising the residues 40-61 was deduced from automated and manual sequence analyses. The Mi-VIII-specific glycophorin A was found to exhibit an arginine .fwdarw. threonine exchange at position 49. The threonine residue was found to be glycosylated. Hemagglutination and hemagglutination inhibition assays demonstrated that one of the Mi-VIII-characteristic antigenic determinants (Anek) is located within the residues 40-61 of glycophorin A. Furthermore, erythrocytes from the two Mi-VIII heterozygotes reacted only weakly with anti-EnaKT sera, suggesting that the Mi-VIII-specific glycophorin A does not express the EnaKT antigen that is located within the positions 46-56 of normal glycophorin A. Our data suggest that the Mi-VIII-specific glycophorin A represents the evolutionary link between normal glycophorin A and the Mi-VIII-specific molecule which exhibits arginine .fwdarw. threonine and tyrosine .fwdarw. serine exchanges at the positions 49 and 52, respectively. Our data also provide an explanation for the close serological similarity between Mi-VII and Mi-VIII erythrocytes.

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