Characterization of the Ss sialoglycoprotein and its antigens in Rhnull erythrocytes

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Autoimmune hemolytic anemia caused by anti "e": A challenge: A case report with review of literature

Autoimmune hemolytic anemia (AIHA) is featured by short red cell survival due to autoantibodies. AIHA caused by anti 'e' is a tough clinical situation as antigen 'e' is a highly prevalent antigen. The present case highlights the same and different issues related to it.

Molecular biology of the Rh blood group system

Rh molecular biology has made many advances since the first Rh cDNA was cloned in 1990. This review summarizes the current knowledge concerning the molecular basis of Rh antigenicity, D-epitope expression, and the structures of the Rh genes and proteins. Although many recent reviews have appeared regarding these subjects, advances in Rh protein function that have been published within the last 12 months have had a fundamental impact on the future direction of Rh research. In November 2000, an article described the role of Rh proteins in ammonium transport, which has remained undescribed in vertebrates, except for non-specific transport via K+ channels. The recent identification of nonerythroid Rh proteins, their expression in diverse tissues, and notably polarized epithelial and endothelial cells will be of broad functional significance and will greatly increase our understanding of the role of Rh in ammonium transport and the biology of ammonium metabolism as a whole. The advances in Rh molecular genetics have enabled the development of diagnostic tests in the clinic. At present, this is largely confined to the prenatal diagnosis of fetal blood group status in alloimmunized pregnancies, but could be extended to the noninvasive prenatal testing of all D-negative pregnant women and eventually, perhaps, to all patient and donor blood.

Blood groups and their function

The function(s) assigned to red blood cell membrane components is based on an observed effect in the red cells that lack the component, comparison of the protein sequence (predicted from the nucleotide sequence of the gene) to proteins of known function, and extrapolation of function of the component in other cells. The functions are varied and include membrane structure, transport, receptor, adhesion, enzyme activity, complement components, complement regulation and glycocalyx formation. Several components have more than one function.

The Rh blood group system: a review

The Rh blood group system is one of the most polymorphic and immunogenic systems known in humans. In the past decade, intense investigation has yielded considerable knowledge of the molecular background of this system. The genes encoding 2 distinct Rh proteins that carry C or c together with either E or e antigens, and the D antigen, have been cloned, and the molecular bases of many of the antigens and of the phenotypes have been determined. A related protein, the Rh glycoprotein is essential for assembly of the Rh protein complex in the erythrocyte membrane and for expression of Rh antigens. The purpose of this review is to provide an overview of several aspects of the Rh blood group system, including the confusing terminology, progress in molecular understanding, and how this developing knowledge can be used in the clinical setting. Extensive documentation is provided to enable the interested reader to obtain further information.

RH blood group system and molecular basis of Rh-deficiency

Rhesus (Rh) antigens are defined by a complex association of membrane polypeptides that are missing or severely deficient from the red cells of rare Rhnull individuals who suffer a clinical syndrome of varying severity characterized by abnormalities of the red cell shape, cation transport and membrane phospholipid organization. The Rhnull phenotype is an inherited condition that may arise from homozygosity either for a 'suppressor' gene unrelated to the RH locus ('regulator type') or for a silent allele at the RH locus itself ('amorph type'). A current model suggests that the proteins of the Rh complex (Rh, RhAG, CD47, LW, GPB) are assembled by non-covalent bonds and that it is not assembled or transported to the cell surface when one subunit is missing. Rh and RhAG proteins belong to the same protein family and are quantitatively the major components that form the core of the complex, which is firmly linked to the membrane skeleton. Molecular analysis of Rhnull individuals has revealed that abnormalities occur only at the RHAG and RH loci, without alteration of the genes encoding the accessory chains. Mutations of the RHAG gene, but not of RH, occur in all Rhnull individuals of the regulator type (including Rhmod) investigated so far (13 cases), strongly suggesting that RHAG mutants act as 'suppressors' and not as transcriptional regulators of the RH genes and that variable expression of the RHAG alleles may account for the Rhmod phenotypes (exhibiting weak expression of Rh antigens). Conversely, mutations of the RHCE gene, but not of RHAG, occur in two unrelated Rhnull individuals of the amorph type, supporting the view that RH mutants result from a 'silent' allele at the RH locus. These findings strongly support the Rh complex model since when either the Rh or RhAG protein is missing, the assembly and/or transport of the Rh complex is defective. Transcriptional as well as post-transcriptional mechanisms may account for the molecular abnormalities, but experimental evidence based on expression models is required to test these hypotheses, in the hope that they may help to clarify the biological role of the Rh proteins in the red cell membrane.

Insights into the structure and function of membrane polypeptides carrying blood group antigens

In recent years, advances in biochemistry and molecular genetics have contributed to establishing the structure of the genes and proteins from most of the 23 blood group systems presently known. Current investigations are focusing on genetic polymorphism analysis, tissue-specific expression, biological properties and structure-function relationships. On the basis of this information, the blood group antigens were tentatively classified into five functional categories: (i) transporters and channels, (ii) receptors for exogenous ligands, viruses, bacteria and parasites, (iii) adhesion molecules, (iv) enzymes and, (v) structural proteins. This review will focus on selected blood groups systems (RH, JK, FY, LU, LW, KEL and XK) which are representative of these classes of molecules, in order to illustrate how these studies may bring new information on common and variant phenotypes and for understanding both the mechanisms of tissue specific expression and the potential function of these antigens, particularly those expressed in nonerythroid lineage.

Adherence of erythrocytes during exflagellation of Plasmodium falciparum microgametes is dependent on erythrocyte surface sialic acid and glycophorins

Malaria male gametocytes within a newly ingested infected blood meal in the mosquito midgut emerge from erythrocytes and extrude approximately eight flagellar microgametes in a process termed exflagellation. In culture, and in blood removed from infected patients, emerging microgametes avidly adhere to neighboring uninfected and infected erythrocytes, as well as to emerged female macrogametes, creating "exflagellation centers". The mechanism of erythrocyte adherence is not known nor has it been determined for what purpose microgametes may bind to erythrocytes. The proposition of a function underlying erythrocyte adherence is supported by the observation of species-specificity in adhesion: microgametes of the human malaria Plasmodium falciparum can bind human erythrocytes but not chicken erythrocytes, whereas avian host Plasmodium gallinaceum microgametes bind chicken but not human erythrocytes. In this study we developed a binding assay in which normal, enzyme-treated, variant or null erythrocytes are identified by a cell surface fluorescent label and assayed for adherence to exflagellating microgametes. Neuraminidase, trypsin or ficin treatment of human erythrocytes eliminated their ability to adhere to Plasmodium falciparum microgametes, suggesting a role of sialic acid and one or more glycophorins in the binding to a putative gamete receptor. Using nulls lacking glycophorin A [En(a-)], glycophorin B (S-s-U-) or a combination of glycophorin A and B (Mk/Mk) we showed that erythrocytes lacking glycophorin B retain the ability to bind but a lack of glycophorin A reduced adherence by exflagellating microgametes. We propose that either the sialic acid moiety of glycophorins, predominantly glycophorin A, or a more complex interaction involving the glycophorin peptide backbone, is the erythrocyte receptor for adhesion to microgametes.

A Novel Single Missense Mutation Identified Along the RH50 Gene in a Composite Heterozygous Rhnull Blood Donor of the Regulator Type

Rare individuals who lack all of the Rh blood group antigens are called Rhnull and may be classified as “regulator” or “amorph” types. The suppression of Rh antigen expression for regulator types may be attributed to mutations of the RH50gene, which is independent of the RH locus. The RH50 gene encodes a glycoprotein that interacts with the Rh proteins to form a functional complex within the red blood cell membrane. This report describes an RH50 gene mutation for a previously unclassified Rhnull donor. Sequencing cDNA clones from Rh50 mRNA revealed a single base change (G836A) yielding a missense and nonconservative mutation (Gly279Glu) within a predicted hydrophobic domain for this membrane protein. Genomic DNA studies using polymerase chain reaction (PCR) restriction analysis and sequencing showed that the Rhnull propositus was a composite heterozygote for this mutation, carrying two alleles with the A and G at nucleotide 836, respectively. In contrast, cDNA studies showed that only the A836 sequence was present, suggesting that the second allele with G836 was apparently silent (no transcript detected). Family studies showed that the mutant RH50 allele (836A) was inherited maternally, whereas the silent RH50 allele (836G) was from paternal transmission. These findings provide further evidence that rare but diverse genetic alterations may occur along the RH50 gene where the Rhnull syndrome of the regulator type occurs. The single amino acid change (Gly to Glu) provides insight into the critical value of these residues for assembly of the Rh antigen complex within the membrane.

Defining the Rh blood group antigens. Biochemistry and molecular genetics

The Rh blood group antigens (D, Cc and Ee series) are carried by a family of non glycosylated hydrophobic transmembrane proteins of 30-32 kDa which are missing from the red cells of rare Rhnull individuals that express several membrane defects. The structure of these proteins has been deduced from cDNA cloning and studies have shown that the Rh proteins are erythroid specific and share no sequence homology with any known protein. The RhD and non-D proteins exhibit 92% sequence identity and their predicted membrane topology is similar as most of the molecules appear to reside between the leaflets of the phospholipid bilayer with only short hydrophilic loops connecting the twelve putative transmembrane helices. The RHD and RHCE genes encoding the Rh proteins (D and Cc/Ee, respectively) are organized in tandem on chromosome 1p34-p36 and most likely derived by duplication of a common ancestral gene. This concept is supported by the identification of RH-like genes in non human primates. The human RH locus is best described as a two-gene model in which all RhD-positive and most RhD-negative haplotypes are composed of two (RHD and RHCE) or only one (RHCE) structural genes, respectively. The RHD gene encodes the D protein and the RHCE gene encodes the C/c and E/e proteins presumably by alternative splicing of a pre messenger RNA. The correlation between the blood group D epitopes and the amino acid polymorphism of the Rh proteins is not yet established, but amino acid polymorphisms at positions 103 and 226 determine the molecular basis for the C/c (Ser-->Pro) and E/e (Pro-->Ala) specificities, respectively. Most variants analyzed so far are caused by gene conversion which appears as the principal mechanism responsible for polymorphism and gene diversity in the RH system. However, gene deletions have also been found in some occasions. To date, all Rhnull phenotypes investigated most likely result from transcriptional regulatory mechanisms that are not yet understood. Rhnull individuals suffer a clinical syndrome of varying severity and their red cells are characterized by morphological and functional abnormalities of cation transport and phospholipid asymmetry. In addition, several membrane components including the Rh proteins and other glycoproteins recently characterized (Rh50 glycoprotein, CD47, glycophorin B, Duffy, LW) are absent or severely decreased on these cells. These findings suggest that the Rh proteins are assembled into a multimeric complex with these glycoproteins and further studies should clarify the role in biosynthesis and the potential function of each component in this complex.

Biochemical aspects of the blood group Rh (rhesus) antigens

Despite their importance in clinical haematology, the details of the structures and possible functions of the proteins associated with Rh antigen expression have only recently begun to emerge. The antigens are carried by a multimeric complex between a M(r) 30,000 polypeptide which is not glycosylated (the Rh30 polypeptide), and a heavily glycosylated glycoprotein (the Rh50 glycoprotein). The N-terminal amino acid sequences of the two types of proteins were determined and used to isolated cDNA clones. The Rh30 and Rh50 proteins are both very hydrophobic membrane proteins, each containing up to 12 membrane spans. The two proteins are homologous in sequence and clearly belong to the same family. They are erythroid-specific and not related to any other known family of proteins. The Rh30 polypeptides are the genetic determinants of Rh blood group antigen activity. One polypeptide (Rh30A) is probably associated with CcEe antigen activity, while another (Rh30B) is responsible for the D antigen. The proteins have structures typical of transporters but their functions are still unclear. A number of other red cell membrane proteins (LW, CD47, glycophorin B and Fy) show alterations in red cells lacking Rh antigens (Rhnull). These proteins may have a role in the biosynthesis or function of the Rh30 and Rh50 proteins.

The abundance and organization of polypeptides associated with antigens of the Rh blood group system

Twelve murine monoclonal antibodies, which react with human red cells of common Rh phenotype but give weak or negative reactions with Rh null erythrocytes, were used in quantitative binding assays and competitive binding assays to investigate the abundance and organization of polypeptides involved in the expression of antigens of the Rh blood group system. Antibodies of the R6A-type (R6A, BRIC-69, BRIC-207) and the 2D10-type (MB-2D10, LA18.18, LA23.40) recognize related structures and 100,000-200,000 molecules of each antibody bind maximally to erythrocytes of common Rh phenotype. Antibodies of the BRIC-125 type (BRICs 32, 122, 125, 126, 168, 211) recognize structures that are unrelated to those recognized by R6A-type and 2D10-type antibodies and between 10,000 and 50,000 antibody molecules bind maximally to erythrocytes of the common Rh phenotype. The binding of antibodies of the R6A-type and the 2D10-type, but not of antibodies of the BRIC-125-type could be partially inhibited by human anti-D antibodies (polyclonal and monoclonal) and a murine anti-e-like antibody. These results are consistent with evidence (Moore & Green 1987; Avent et al., 1988b) that the Rh blood group antigens are associated with a complex that comprises two groups of related polypeptides of M(r) 30,000 and M(r) 35,000-100,000, respectively, and suggest that there are 1-2 x 10(5) copies of this complex per erythrocyte. The polypeptide recognized by antibodies of the BRIC-125 type is likely to be associated with this complex.

Immunoblotting of human red cell membranes: detection of glycophorin B with anti-S and anti-s antibodies

Human anti-S and anti-s eluates bound to glycophorin B on immunoblots from membranes of S+ and s+ red cells, respectively. Eluates of human anti-S were more efficiently prepared from sensitized trypsin-treated cells than from sensitized untreated cells. The results of immunoblotting membranes from enzyme-treated cells confirmed the serological findings: S and s antigens were not affected by treatment with trypsin or sialidase but were destroyed or much depressed by treatment with papain, pronase or alpha-chymotrypsin. Immunoblotting with anti-S or anti-s of membranes from cells with unusual MNS phenotypes confirms the involvement of glycophorin B in hybrid glycophorins; the existence of such hybrid glycophorins was deduced previously from serological work or immunoblotting with monoclonal antibodies. The presence of s-active glycophorin B in glycophorin (B-A)Dantu, in glycophorin BMiIII and in glycophorin (A-B)MiV was confirmed. The bands observed when Mit+ membranes were immunoblotted with anti-S supports the suggestion from serological work that the Mit antigen is associated with an altered S antigen.

Murine monoclonal antibodies against a unique determinant of erythrocytes, related to Rh and U antigens: expression on normal and malignant erythrocyte precursors and Rhnull red cells

Three murine monoclonal antibodies (Mabs) MB-2D10, LA-18.18 and LA-23.40 were prepared. They reacted with red cells of all common and most rare blood-group phenotypes, with the exception of those of the RhnullU negative and RhmodU negative phenotypes. So far, only a single example of an alloantibody (Duclos or anti-Rh38) of a similar specificity has been found. Serological studies indicated that the Mabs were probably not directed against an antigenic determinant of Rh polypeptides, the LWab glycoprotein or glycophorin B, all structures absent from or aberrantly expressed on Rhnull red cells. The antigen was found to be erythrocyte-specific, and was also present on pro-erythroblasts, erythroblasts and malignant erythroblastoid cells but not on erythroid progenitors in the bone marrow. The Mabs were found to block each other in an immune rosette method and are thus probably directed against the same epitope or against neighbouring epitopes on the same structure. In immunochemical studies, MB-2D10 precipitated the 30-32 kDa Rh polypeptides from red cell membranes and a protein or proteins which formed diffuse and overlapping bands in SDS-polyacrylamide gel electrophoresis, with Mrs of 40-200 kDa (probably the Rh-related glycoproteins). Under certain experimental conditions glycophorin B appeared to be coprecipitated. The 2D10 structure, detected by the Mabs, seems to be part of a complex of proteins and/or glycoproteins, which includes Rh polypeptides, the LWab glycoprotein and glycoproteins recognized by various Mabs with Rh-related specificities. In the red cell membrane, the complex may be associated with glycophorin B.

Regulator genes affecting red cell antigens

Several mechanisms may be involved to explain the action of genes that regulate the expression of red cell antigens. When carbohydrate antigens are involved, lack of an enzyme in the biochemical pathway prevents formation of the precursor for the next and following steps of that path, or, alternatively, addition of an extra sugar to the immuno-dominant sugar may produce a new structure in which the expression of the expected antigen is masked. Thinking of genetic rather than biochemical interference, a regulator gene may "switch-off" the action of a structural gene, and this mechanism could involve the upset of repressor and/or derepressor genes. The mechanisms for the regulator genes described in this article are unknown. The effect of XGR is limited to red cells: the expression of 12E7 antigen on other tissues and cells, other than red cells, is invariable. The reported effects of XOr and XQ are for red cells, but it is unlikely that other cells and tissues have been studied intensively; propositi with these regulator genes are much rarer than people informative for XGR and In(Lu). The effects of In(Lu) are not limited to red cells but have been shown to regulate the expression of p80 on some white cells. Most of the abnormalities in Rhnull cells appear to be associated with the lack of the Rh antigens and lack of Rh proteins. The hypothesis of a functional complex involving Rh, lack of which affects incorporation of apparently unrelated proteins into the red cell membrane, is an attractive idea. Studies of the similar phenotype, Rhmod, suggest that some Rh specificities can be present in cells that appear to be as abnormal, serologically and morphologically, as Rhnull cells. Perhaps some polypeptides are functionally more important than others and perhaps all polypeptides required for the functional efficiency of the Rh complex have not yet been identified. Lack of Lutheran antigens is not always accompanied by modification of other red cell antigens. As suggested by Telen and green, if In(Lu) acts via a single mechanism, then that mechanism differs from that of XS2. Certainly the mechanisms of In(Lu) and XS2 differ in their action on the expression of CD44 or p80 antigens. The red cell surface is well charted territory, familiar to serologists, immunologists, biochemists, and geneticists. It still provides an excellent model for study of cell surface antigens and for the regulator genes described above that modify expression of some red cell antigens.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood group-active surface molecules of the human red blood cell

The surface of the human red blood cell is dominated by a small number of abundant blood group active proteins. The major proteins are the anion transport protein (band 3) which has AB(H) activity, and Glycophorin A which has MN activity. Band 3 and Glycophorin A are of equal abundance in the normal red cell membrane (approximately 10(6) copies of each) and the two proteins may associate together as a complex. The glucose transporter (band 4.5) had AB(H) activity and there are about 5 x 10(5) copies/red cell. Several polypeptides associate together to form the Rh complex. The major components of this complex (abundance 1-2 x 10(5) copies/red cell) are polypeptides of Mr 30,000, polypeptides of Mr 45,000-100,000 and Glycophorin B. The antigens of the Rh blood group system appear to be associated with the polypeptides of Mr 30,000 and those of Mr 45,000-100,000 (the latter also express AB(H) activity). Glycophorin B expresses the blood group 'N' antigen and the Ss antigens. Glycophorins C and D carry the Gerbich antigens and, together, these polypeptides comprise approximately 10(5) copies/red cell. The complete protein sequence of all the above-mentioned proteins is known, except for the Mr 30,000 and Mr 45,000-100,000 polypeptides of the Rh complex for which only partial sequences are available, and Glycophorin D, the sequence of which can be inferred from that of Glycophorin C. Several of the minor blood group active proteins at the red cell surface (abundance less than 1.2 x 10(4)/red cell) have been the subject of recent studies. The polypeptide expressing Cromer-related blood group antigens has been identified as decay-accelerating factor and that carrying the Ina/Inb antigens as CD44. The protein sequence of both of these proteins has been deduced form nucleotide sequencing. The polypeptides expressing Kell antigens, Lutheran antigens, Fy antigens, and LW antigens have also been identified and partially characterised.

Properties of the blood group LW glycoprotein and preliminary comparison with Rh proteins

The major component immunoprecipitated from human red cell membranes by murine monoclonal antibodies (BS46 and BS56) against the LW blood group antigens is a 42,000 mol. wt glycoprotein. Upon digestion by an N-glycanase the LW component migrated as a 25,000 mol. wt component on SDS gels, whereas treatment by an O-glycanase led only to a small size reduction (2000). These data suggest that the LW glycoprotein might carry approximately eight to nine N-linked sugar chains and only a few (one or two) O-linked oligosaccharide chains. A minor component of 31,000 mol. wt was also identified in the LW immunoprecipitate. Preliminary analyses by two-dimensional peptide mapping indicate that the 31,000 mol. wt polypeptide is identical to authentic Rh proteins, therefore raising the possibility that the Rh and LW antigens are associated in the membrane as a functional complex called Rh cluster. Since the N-deglycosylated form of the LW and RhD proteins have different sizes (25,000 vs 31,000-32,000 respectively) and since their externally 125I-labelled domains have different two-dimensional peptide maps, it is concluded that LW is probably not a simple glycosylated form of the Rh proteins.

Protein-sequence studies on Rh-related polypeptides suggest the presence of at least two groups of proteins which associate in the human red-cell membrane

The Rh D blood-group antigen forms part of a complex, involving several other polypeptides, that is deficient in the red cells of individuals who lack all the antigens of the Rh blood-group system (Rhnull red cells). These include components recognized by anti-(Rh D) antibodies and the murine monoclonal antibodies R6A and BRIC 125. We have carried out protein-sequence studies on the components immunoprecipitated by these antibodies. Anti-(Rh D) antibodies immunoprecipitate an Mr-30,000-32,000 polypeptide (the D30 polypeptide) and an Mr-45,000-100,000 glycoprotein (D50 polypeptide). Antibody R6A immunoprecipitates two glycoproteins of Mr 31,000-34,000 (R6A32 polypeptide) and Mr 35,000-52,000 (R6A45 polypeptide). The D30 and R6A32 polypeptides were found to have the same N-terminal amino acid sequences, showing that they are closely related proteins. The D50 polypeptide and the R6A45 polypeptide also had indistinguishable N-terminal amino acid sequences that differed from that of the D30 and R6A32 polypeptides. The putative N-terminal membrane-spanning segments of the two groups of proteins showed homology in their amino acid sequence, which may account for the association of each of the pairs of proteins during co-precipitation by the antibodies. Supplementary data related to the protein sequence have been deposited as Supplementary Publication SUP 50417 (6 pages) at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1988) 249, 5.

Isolation of cDNA clones for human erythrocyte membrane sialoglycoproteins alpha and delta

We have isolated almost full-length cDNA clones corresponding to human erythrocyte membrane sialoglycoproteins alpha (glycophorin A) and delta (glycophorin B). The predicted amino acid sequence of delta differs at two amino acid residues from the sequence determined by peptide sequencing. The sialoglycoprotein delta clone we have isolated contains an interrupting sequence within the region that gives rise to the cleaved N-terminal leader sequence for the protein and represents a product that is unlikely to be inserted into the erythrocyte membrane. Comparison of the cDNA sequences of alpha and delta shows very strong homology at the DNA level within the coding regions. The two mRNA sequences are closely related and differ by a number of clearly defined insertions and deletions.

The Dantu erythrocyte phenotype of the NE variety. II. Serology, immunochemistry, genetics, and frequency

Red cells (RBC) possessing the low-frequency MNSs antigen Dantu from 36 Black individuals (21 propositi) were found to exhibit the NE variety of this phenotype, as judged from the electrophoretic glycophorin (GP) pattern, described in an accompanying article, and/or from the polybrene test which detects the decreased NeuAc level of these RBC. All known DantuNE RBC (53) exhibit the phenotype M+N+. This finding as well as family studies and immunochemical investigations demonstrate that the DantuNE allele encodes a blood group M-specific GP A. Thus, the strongly decreased GP A level of RBC from DantuNE heterozygotes represents the product of the Dantu allele and its normal counterpart. It is suggested that the formation of a complex with the anion channel protein (band 3) represents the prerequisite for optimum incorporation of GP A into normal RBC membranes. The hybrid GP in DantuNE RBC, produced in large quantity, might suppress the incorporation of GP A in a cis and trans manner via the formation of a complex with band 3. The hybrid GP in DantuNE RBC lacks U activity, but expresses N activity and a qualitatively altered s antigen, thus proving its GP B-GP A hybrid nature in conjunction with data described in the accompanying article. Screening of ficin-treated RBC with Vicia lectin revealed that the Dantu phenotype exhibits a frequency of about 0.005 in American Blacks and less than 0.001 in Germans.

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.