Structures of Miltenberger class I and II specific major human erythrocyte membrane sialoglycoproteins

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Abstract
The N‐terminal structures of the Miltenberger (Mi‐) blood group class I and II specific human MN erythrocyte membrane sialoglycoproteins were determined by manual sequencing of tryptic glycopeptides and various secondary fragments. The Mi‐I and Mi‐II active glycoproteins were found to exhibit a threonine → methionine and threonine → lysine exchange, respectively, at position 28 which prevents N‐glycosylation of asparagine 26. Due to the absence of the N‐glycosidic oligosaccharide chain, the monomeric form of the Mi‐I and Mi‐II specific glycoproteins possesses a slightly increased sodium dodecyl sulfate/polyacrylamide gel electrophoretic mobility, in comparison to its normal counterpart. Serological studies suggest that antibodies, specific for Mi‐I or Mi‐II red cells, react with the structurally altered region of the MN glycoprotein.