Modification of Amino Groups of Human‐Erythrocyte Glycoproteins and the New Concept on the Structural Basis of M and N Blood‐Group Specificity

Abstract

1.Various kinds of modification of amino groups of M and N blood group glycoproteins abolished their capacity to inhibit rabbit and human anti-M and anti-N sera.2. The reversible modification of amino groups revealed that M and N blood group activity was restored after the removal of amino-group-blocking residues.3. Modification of amino groups had an entirely different effect on the reactivity of red cell glycoproteins with Vicia graminea agglutinin. The serological activity of N glycoprotein towards Vicia graminea anti-N agglutinin was unchanged, whereas the weak activity of M glycoprotein towards this anti-N agglutinin was increased to the level of that of N glycoprotein.4. These results indicate that there is a structural difference between M and N glycoproteins, which resides beyond the oligosaccharide chains. It suggests in turn that M and N blood group specificity is determined by amino acid sequence in the peptide chains of red cell glycoproteins.The M and N blood group receptors are located on the major glycoprotein of human erythrocyte membrane. It has been known that for M and N blood group activity sialic acid residues are required [l -71, and that this activity is associated with alkali-labile, sialic-acid-rich oligosaccharide chains [8 -101. Springer et al. [11,12] reported that N receptors were differentiated from M receptors by the presence of terminal b-galactosyl residues. The small amount of specific receptors among many unspecific oligosaccharide chains could justify the fact that no conclusive chemical evidence for the difference in structure of oligosaccharides of M and N glycoproteins has been reported so far. We found [13] that modification of amino groups of the glycoproteins abolished their capacity to inhibit rabbit anti-M and anti-N sera, and this finding was confirmed later by Ebert et ul. [4]. It drew attention to the possible role of the peptide chain in M and N blood group activity.The activity of red cell glycoproteins against anti-N lectin from Viciu graminea seeds (NVg activity) has entirely different structural requirements. The NV, activity is also confined to alkali-labile Abbreviation. Nyg activity, the serological activity directed toward Viciu graminea anti-N agglutinin.oligosaccharide chains [8], but is significantly enhanced after the release of sialic acid from the glycoproteins [14-161. The increase of Nvg activity on desialization of M and N antigens reached for both antigens a similar level. The Nvg activity was not affected by the modification of amino groups of N glycoprotein To shed more light on the structural differences between M and N antigenic determinants, further experiments on the modification of erythrocyte glycoprotein amino groups were undertaken, with special attention to the following problems. (a) The significance of amino groups in the reaction of glycoproteins with human anti-M and anti-N sera; (b) the reversibility of the serological effects of modification of amino groups, and (c) the effect of modification of amino groups on the NYg activity of...

Effect of Periodate Oxidation on Specific Activities and Carbohydrate Components of Human Blood Group N- and M-Specific Glycoproteins and Glycopeptides

“…Our findings indicate that a full comple ment of intact terminal carbohydrates is a precondition for undiminished N-and Mactivities determined with animal antisera and also show that Vicia specificity is de stroyed by even mild periodate oxidation [37,43], The involvement of terminal ß-G&\ in Vicia-and blood group N-specificities has been challenged by Lisowska and Duk [16,17] by the statement that the N and M glycoproteins contained no terminal sug ars other than NAN. However, their own results listed in table I [16] showed an 8% destruction of neutral nonhexosamine sug ars, during their first periodate oxidation step.…”

“…They were less well inhibitable by oligosaccharide fractions than some but not all other anti-M sera [31]. They indicated excellent transformation of precursor antigens to M-specific substances, however, upon their incubation with serum transferases from M donors [4], It has been stated that Lys influences N-and M-specificities decisively, its e-amino group was thought to be part of the N-and M-specific determinants [16,17] …”

Reactions of Murine Monoclonal Antibodies to Blood Group MN Antigens

“…presence of N-acetyl neuraminic acid (NANA) attached to a protein backbone [2,3], While some investigators presented evidence that specificity of M and N antigens is determined by carbohydrate structures [4,5] and also glycolipids [6], it now appears that both carbohydrate and amino acid residues also involved in formation of M and N determinants [7][8][9][10][11], One group of investigators found no difference in the sialic acid content of M and N RBC [12], which argues against the thesis that the carbohy drates are entirely responsible for M and N activities, while another group [13] found that there was a signifi cant difference in the sialic acid content and that M RBC glycopeptides have more components than N RBC glycopeptides. Significantly, treatment with neuraminidase [14,15] which removes NANA from the surface of RBC or chemial modification of amino groups [ 16] which may also damage carbohydrates, destroy M and N blood group activity.…”

Specific Antibodies for Desialized M and N Blood group Antigens

“…The modification of amino groups of M and N glycoproteins also destroys their blood group activity [5,13]. Recent stud ies, carried out in Uhlenbruck's [3,4] and our [10,11] laboratory, indicate that the structural difference between M and N antigens resides rather in the polypeptide chain than in the oligosaccharides. If this assumption is correct, the desialized M and N glycoproteins should have different struc tures, and should show different antigenic properties.…”