Studies on Miltenberger class III, V, Mv and Mk red cells. I. Sodium-dodecylsulfate polyacrylamide gel electrophoretic investigations

The low-incidence MNS antigens M(v), s(D), and Mit arise from single amino acid substitutions on GPB

BACKGROUND

GPB carries 'N' at its N:-terminus and S and s, determined by a polymorphism at amino acid position 29 (Met29Thr). The low-incidence antigens M(v), s(D), and Mit are associated with weakened expression of S and/or s, and the purpose of this study was to define their molecular bases.

METHODS

The GPB gene (GYPB) was sequenced after RT-PCR of RNA from four samples: two M(v)+, one s(D)+, and one Mit+. The point mutations observed were confirmed by sequencing of genomic DNA from these and other examples of s(D)+ and Mit+ samples.

RESULTS

A point mutation of 65C>G observed in the M(v)+ samples predicted a change of Thr3Ser. A mutation of C>G at nucleotide 173 of the GYPB coding sequence, observed in two s(D)+ samples, predicted a change of Pro39Arg. Three Mit+ samples showed a nucleotide substitution of 161G>A, which predicted a change of Arg35His. Altered expression of S or s was confirmed by serologic tests.

CONCLUSION

These results confirm that Arg35 is important for full expression of S. Pro39 and, surprisingly, Thr3 are also important for full expression of s. Furthermore, Thr3 must be essential for expression of 'N,' as M(v)+ RBCs lack 'N.'

Miltenberger class IX of the MNS blood group system

Mi.IX is a new phenotype in the Miltenberger series of the MNS blood group system with a frequency of 0.43% in Denmark. Mi.IX red cells are Mur+ but do not express any of the other established Miltenberger determinants. They react with a new antibody, anti-DANE, which defines a determinant present on Mi.IX cells but not on cells of other Miltenberger phenotypes. Four Mi.IX propositi have been found. Their families show that MiIX is inherited with a MS complex (lod score 3.69 at theta = 0.00) which produces a trypsin-resistant M antigen. DANE has been allotted the ISBT number 002032 (MNS32). Serological and immunochemical studies with human and monoclonal antibodies to various determinants on glycophorin A (GPA) suggest that Mi.IX is associated with an aberrant GPA molecule that lacks the trypsin cleavage site at amino-acid residue 39, retains the chymotrypsin cleavage site at residue 34 and has an apparent Mr of about 1,000 less than normal GPA. It is proposed that this Mi.IX molecule has an amino acid and possibly also a glycosylation change in the region of amino-acid residues 35-39.

Identification by immunoblotting of the erythrocyte membrane sialoglycoproteins that carry the Vw and Mur antigens

Immunoblotting of the separated membrane components of MiI erythrocytes with anti-Vw identified a band of Mr 40,000 with a mobility close to that of beta-sialoglycoprotein corresponding to the abnormal alpha-sialoglycoprotein present in MiI cells. A comparison of results obtained when MiIII erythrocytes were immunoblotted with anti-Mur, anti-s and the monoclonal antibody R1.3, indicated that the Mur antigen is located on the abnormal delta-sialoglycoprotein of Mr 36,000 in MiIII erythrocytes. Prior treatment of MiI erythrocytes with neuraminidase resulted in an increase in the intensity of staining of the anti-Vw reactive component. This was consistent with the enhanced reactions observed in haemagglutination tests with neuraminidase-treated erythrocytes. The mobility of the Vw component was reduced when erythrocytes were pre-treated with low concentrations of neuraminidase but increased when higher concentrations of neuraminidase were used.

A family study of multiple mutations of alpha and delta glycophorins (glycophorins A and B)

Glycophorins alpha and delta are the carriers of the antigens of the MNSs blood system; this report documents the presence of three glycophorin mutations in two individuals of a 16 member family. Erythrocytes were examined by serology, sodium dodecyl sulfate electrophoresis, and immunoblotting. The inheritance pattern and immunoblot profile revealed: (1) A variant Dantu glycophorin showed properties consistent with a delta-alpha glycophorin hybrid structure, previously noted in other individuals. The gene responsible for the Dantu glycophorin in this family is linked to a gene coding for an M-specific alpha glycophorin. (2) Another variant glycophorin, Mi-III glycophorin, was first revealed by immunoblotting and subsequently confirmed by erythrocyte antigen typing. This autosomal dominant trait is associated with N blood group activity and the inheritance pattern indicates that it could be a variant of delta glycophorin. (3) In the individuals with both Dantu and Mi-III glycophorins a delta glycophorin deficiency was observed suggesting that a deletion or alteration of delta gene may exist cis to the Dantu gene. Our findings that document clustering of multiple mutations in MNSs gene loci in the propositus family are very unusual as such variants are relatively rare.

Hybrid glycophorins from human erythrocyte membranes. Isolation and complete structural analysis of the novel sialoglycoprotein from St(a+) red cells

Human red cells from donor Pj carry the Sta blood group antigen and an unusual sialoglycoprotein of 24 kDa molecular mass tentatively identified as a hybrid molecule of the anti-Lepore type [Blanchard et al. (1982) Biochem. J. 203, 419-426]. This component is resistant towards proteinase treatment and was purified from trypsin-treated and chymotrypsin-treated Pj erythrocytes. The molecule is composed of 99 amino acid residues whose alignment was established following manual and automatic sequencing of cyanogen bromide, trypsin, chymotrypsin and V8 proteinase peptides. The polypeptide chain comprises residues 1-26/28 of glycophorin B and residues 59/61-131 of glycophorin A. The sugar composition resembles that of glycophorin B, indicating the absence of an N-glycosidic chain. Identical sequences were obtained from analyses of the 24-kDa component purified from unrelated St(a+) donors. These results support the hypothesis that glycoprotein Pj represents a B-A hybrid molecule which is encoded by a new gene product resulting from an unequal crossing-over between the genes coding for the polypeptide chains of the glycophorins A and B. The novel molecule carries both N and Sta blood group antigens. The N activity is clearly understandable from the sequence of the five N-terminal residues (Leu and Glu at positions 1 and 5 respectively). Inhibition studies with the untreated and chemically modified hybrid glycoprotein indicate that the Sta determinant is located within residues approximately 25-30 of the molecule, which corresponds to the newly formed sequence found neither in glycophorin A nor in glycophorin B.

Structural analysis of the major human erythrocyte membrane sialoglycoprotein from Miltenberger class VII cells

The major human erythrocyte membrane sialoglycoprotein (glycophorin A or MN glycoprotein) was purified from the red blood cells of an individual, homozygous for the Mi-VII gene in the Miltenberger subsystem of the MNSs blood-group system. The complete structure of a tryptic peptide comprising the residues 40-61 of glycophorin A was deduced from manual sequence analyses. The Mi-VII-specific glycophorin A was shown to exhibit an arginine----threonine and a tyrosine----serine exchange at the positions 49 and 52 respectively. The threonine-49 residue was found to be glycosylated. Inhibition assays demonstrated that one of the Mi-VII-specific antigen determinants (Anek) is located within the residues 40-61 of glycophorin A and comprises sialic acid residue(s) attached to O-glycosidically linked oligosaccharide(s). Our data contribute to an understanding of the Miltenberger system and provide an explanation at the molecular level for the previous finding that the erythrocytes from the Mi-VII homozygote lack a high-frequency antigen (EnaKT), located within the residues 46-56 of normal glycophorin A.

The Dantu erythrocyte phenotype of the NE variety. I. Dodecylsulfate polyacrylamide gel electrophoretic studies

Red cell membranes from patient NE, Mr. Dantu and 16 additional Black individuals, positive for the low-frequency MNSs-system antigen Dantu, were studied by dodecylsulfate polyacrylamide gel electrophoretic techniques. The content of the major, blood group M- or N-active sialoglycoprotein (glycophorin A, GP A) was found to be decreased by about 57%. The blood group S- or s-active sialoglycoprotein (GP B) was decreased by about 51% in membranes from proven Dantu/U heterozygotes and not detectable in those from patient NE and other Dantu+U- individuals. Donor NE was shown to exhibit the genotype Dantu/u. Dantu-positive cells exhibit a proteinase-resistant GP B-GP A hybrid with an apparent molecular mass of 29 KDa whose intramembraneous and cytoplasmic domains were shown to be similar to those of GP A. The molar hybrid: GP A ratio in all cells was found to be about 2.4: 1, indicating that the NE variety of the Dantu phenotype is much more frequent than the Ph or MD types. The significance of an additional minor 'new' component (molecular mass 21 KDa) in Dantu+ membranes and the minor component J (molecular mass 22 KDa) occurring in normal and Dantu+U+ GP preparations, but not in those from Dantu+U- cells, has not been resolved. The apparent molecular mass of the anion channel protein (band 3) in all cells of the NE variety was shown to be decreased by about 3 KDa, due to a shortening of carbohydrate chains. This suggests that the hybrid, just like GP A, might form a complex with band 3.

Hybrid glycophorins from human erythrocyte membranes. I. Isolation and complete structural analysis of the hybrid sialoglycoprotein from Dantu-positive red cells of the N.E. variety

The hybrid glycophorin in Dantu-positive human erythrocytes of the N.E. variety was not cleaved by treatment of intact cells with various proteases, in contrast to normal glycophorins. Therefore, it could be purified by phenol/saline extraction of membranes from trypsin-treated and chymotrypsin-treated red cells and subsequent gel filtration in the presence of Ammonyx-LO. The complete structure of the hybrid molecule, comprising 99 amino acid residues, was elucidated by sequence analyses of peptides prepared by chymotrypsin, trypsin, cyanogen bromide or V8 proteinase treatment. The N-terminal 39 residues and the glycosylation of the molecule were found to be indistinguishable from those of blood-group-s-specific glycophorin B. Conversely, the residues 39-99 were shown to be identical with the residues 71-131 of the major blood-group M-active or N-active sialoglycoprotein (glycophorin A). Hemagglutination inhibition assays revealed that the Dantu antigen represents a labile structure. The receptor might be located within the residues approximately 28-40 of the hybrid glycophorin, as judged from the effects of modifications of membranes. Our data provide an explanation for the previous findings that Dantu-positive cells (N.E. type) exhibit a protease-resistant N antigen and a qualitatively altered s antigen.

Gerbich blood group deficiency of the Ge:-1,-2,-3 and Ge:-1,-2,3 types. Immunochemical study and genomic analysis with cDNA probes

Human erythrocytes carry several transmembrane glycoproteins, among which the two minor species associated with the blood group Gerbich (Ge) antigens, GP C and GP D, play pivotal role since they interact with the membrane cytoskeleton and contribute to maintain the normal red cell shape. On the red cells from two categories of homozygous donors lacking the Ge determinants (Ge:-1,-2,-3 and Ge:-1,-2,3), GP C and GP D are missing but instead there is a new glycoprotein, easily detected by SDS/polyacrylamide gel electrophoresis, which exhibits some properties shared by GP C and GP D. This was shown by immunochemical analyses with a murine monoclonal antibody, extraction of the glycoproteins by organic solvents and binding studies with the 125I-labelled Lens culinaris lectin. The red cells from obligate heterozygotes for the Ge:-1,-2,-3 condition also carry this new glycoprotein component but in a much lesser amount than expected on the basis of one gene dose response. Using a cDNA probe containing the coding sequence of human GP C and the entire 3' untranslated region of its mRNA, we have demonstrated by Southern analyses that the Ge:-1,-2,-3 and the Ge:-1,-2,3 conditions are associated with a constant 3-kbp deletion within the GP C gene. Similar studies indicated that this gene is present as a unique copy per haploid genome of Ge-positive control donors (Ge:1,2,3). To account for these data and for the glycoprotein profile of Ge-negative erythrocytes, it is proposed that a unique Gerbich gene encodes for GP C and GP D, either by alternative RNA splicing or by different post-translational events, and that, following a 3-kbp deletion within this gene, a new glycoprotein having properties common to GP C and GP D can be produced.

Characterization of the Ss sialoglycoprotein and its antigens in Rhnull erythrocytes

The Ss sialoglycoprotein (glycophorin B) and its antigens in Rhnull erythrocytes, which lack the Rhesus blood group antigens, due to apparently silent (amorphic type) or independent suppressor (regulator type) genes, were investigated. The quantity of the molecule in amorphic and in regulator type red cell membranes was found to be decreased by about 60%-70%, as judged from sodium-dodecylsulfate polyacrylamide gel electrophoresis. The Ss glycoprotein content in the erythrocytes from heterozygotes (regulator type) was diminished to an extent of about 30%. Confirming and extending previous studies, the S, s, Ux, Uz and 'N' antigens were slightly weakened in Rhnull erythrocytes. The U and Duclos receptors were only slightly or not depressed in amorphic Rhnull cells, but almost absent from or not detectable in those of the regulator type. This demonstrates that an additional alteration, apart from the decreased Ss glycoprotein content of the membranes, accounts for the weakness of these receptors in regulator type cells. We propose the hypothesis that (a) protein(s) encoded by the Rhesus locus form(s) a complex with the Ss glycoprotein. Thus, it (they) might facilitate the incorporation of the Ss glycoprotein into the membrane and also contribute to the complete expression of the U and Duclos antigens in normal cells.

Studies on Mv red cells. II. Immunochemical investigations

The properties of the Mv antigen, a low incidence receptor of the MNSs blood group system, were investigated by serological tests with protease treated red cells and inhibition assays with glycoproteins or peptides from normal and Mv erythrocytes. Our data demonstrate that the Mv receptor represents an allelomorphic form of the 'N' antigen on the Ss sialoglycoprotein, rather than variant of the M receptor on the MN sialoglycoprotein. Anti-Mv plus -N (serum Arm.) reacts with the N, 'N' and Mv antigens, whereas anti-Mv (serum Arch.) is specifically directed against the latter receptor.

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

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 leads to methionine and threonine leads to 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.

Miltenberger Class I and II erythrocytes carry a variant of glycophorin A

The membranes from Miltenberger Class I (Mi I) and II (Mi II) erythrocytes, two rare variants at the blood group MNSs locus, exhibited an abnormal glycoprotein of 32 kDa apparent molecular mass sharply stained by the periodic acid/Schiff procedure and a decreased content of glycoprotein alpha (synonym glycophorin A, glycoprotein MN) as seen on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Purified 125I-labelled Vicia graminea lectin binds to the unusual 32 kDa glycoprotein separated from Mi I and Mi II erythrocyte membrane of blood group NN or MN, but no significant labelling of this band was observed with Mi samples typed MM. On the basis of such lectin-labelling experiments we have described two heterozygous MN, Mi I individuals that carry one copy of an M gene producing a normal alpha-glycoprotein with M-specificity and one copy of a MiI gene producing a 32 kDa glycoprotein with N-specificity. Further investigations have shown that the 32 kDa glycoprotein was immunoprecipitated by two mouse monoclonal antibodies (R18 and R10) reacting specifically with the external domain of glycoprotein alpha. These results demonstrate that Mi I and Mi II erythrocytes carry an unusual variant of glycoprotein alpha.

Pj variant, a new hybrid MNSs glycoprotein of the human red-cell membrane

An unusual glycoprotein variant (Pj) was found inherited through a caucasian family exhibiting atypical N and Nvg blood-group reactivities. Pj erythrocytes are blood-group-MS homozygous and have a normal sialic acid content. On sodium dodecyl sulphate/polyacrylamide-gel electrophoresis the variant contains a new component Pj of 24kDa apparent molecular mass in the monomeric state which is sharply stained by periodic acid/Schiff reagent. Both blood-group-MN (alpha) and -Ss (delta) glycoproteins were present. Homodimers (Pj2) as well as heterodimers with MN-glycoprotein (alpha Pj) and the Ss-glycoprotein (delta Pj) were also identified. The new sialoglycoprotein Pj is trypsin- and chymotrypsin-resistant in situ and carries N- and Nvg- but not M- and S-reactivities. The Pj component is labelled by lactoperoxidase-catalysed radioiodination. A 3H label is also easily introduced into the sialic acid or the galactose and galactosamine of the Pj glycoprotein. It is proposed that the Pj is a hybrid glycoprotein containing the N-terminal end of delta-glycoprotein and the C-terminal end of the alpha-glycoprotein. This proposal is supported by the finding that Pj carries a leucine residue at its N-terminus and is not immunoprecipitated by a monoclonal mouse antibody (R18) reacting specifically with the external domain of glycoprotein alpha. The red cells from the proposita Pj were found positive for a very low frequency MN antigen named Sta.