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

Resistance to malaria through structural variation of red blood cell invasion receptors

The malaria parasite Plasmodium falciparum invades human red blood cells by a series of interactions between host and parasite surface proteins. By analyzing genome sequence data from human populations, including 1269 individuals from sub-Saharan Africa, we identify a diverse array of large copy-number variants affecting the host invasion receptor genes GYPA and GYPB We find that a nearby association with severe malaria is explained by a complex structural rearrangement involving the loss of GYPB and gain of two GYPB-A hybrid genes, which encode a serologically distinct blood group antigen known as Dantu. This variant reduces the risk of severe malaria by 40% and has recently increased in frequency in parts of Kenya, yet it appears to be absent from west Africa. These findings link structural variation of red blood cell invasion receptors with natural resistance to severe malaria.

Blood group antigens on human erythrocytes-distribution, structure and possible functions

Human erythrocyte blood group antigens can be broadly divided into carbohydrates and proteins. The carbohydrate-dependent antigens (e.g., ABH, Lewis, Ii, P1, P-related, T and Tn) are covalently attached to proteins and/or sphingolipids, which are also widely distributed in body fluids, normal tissues and tumors. Blood group gene-specific glycosyltransferase regulate the synthesis of these antigens. Protein-dependent blood group antigens (e.g., MNSs, Gerbich, Rh, Kell, Duffy and Cromer-related) are carried on proteins, glycoproteins and proteins with glycosylphosphatidylinositol anchor. The functions of these molecules on human erythrocytes remain unknown; some of them may be involved in maintaining the erythrocyte shape. This review describes the distribution, structures and probable biological functions of some of these antigens in normal and pathological conditions.

An immunoblotting procedure for screening glycophorins and band 3 protein in the same blots. Identification of glycophorin and band 3 variant forms

An immunoblotting procedure is described which makes it possible to screen multiple blood samples for the presence of glycophorin and band 3 variant forms with altered electrophoretic mobility. The procedure can be simplified by using whole red blood cell hemolysates instead of membranes for SDS-polyacrylamide gel electrophoresis. The use of hemolysates also has the advantage that antigens sensitive to proteolysis are not degraded in vitro. The same nitrocellulose blots were used for immunoenzymatic detection of glycophorins with a set of anti-glycophorin monoclonal antibodies, and for autoradiographic detection of band 3-derived bands with 125I-labeled anti-band 3 monoclonal antibody. The screening of 157 Caucasian blood samples revealed the presence of a slower-migrating form of band 3 in seven cases and variant glycophorin in one case. The variant glycophorin exhibited the features of hybrid glycophorin of B-A type.

Human erythrocyte glycophorins: protein and gene structure analyses

Human RBCs glycophorins are integral membrane proteins rich in sialic acids that carry blood group antigenic determinants and serve as ligands for viruses, bacteria, and parasites. These molecules have long been used as a general model of membrane proteins and as markers to study normal and pathological differentiation of the erythroid tissue. The RBC glycophorins known as GPA, GPB, GPC, GPD, and GPE have recently been fully characterized at both the protein and the DNA levels, and these studies have demonstrated conclusively that these molecules can be subdivided into two groups that are distinguished by distinct properties. The first group includes the major proteins GPA and GPB, which carry the MN and Ss blood group antigens, respectively, and a recently characterized protein, GPE, presumably expressed at a low level on RBCs. All three proteins are structurally homologous and are essentially erythroid specific. The respective genes are also strikingly homologous up to a transition site defined by an Alu repeat sequence located about 1 Kb downstream from the exon encoding the transmembrane regions. Downstream of the transition site, the GPB and GPE sequences are still homologous, but diverge completely from those of GPA. The three glycophorin genes are organized in tandem on chromosome 4q28-q31, and define a small gene cluster that presumably evolved by duplication from a common ancestral gene. Most likely two sequential duplications occurred, the first, about 9 to 35 million years ago, generated a direct precursor of the GPA gene, and the second, about 5 to 21 million years ago, generated the GPB and GPE genes and that involved a gene that acquired its specific 3' end by homologous recombination through Alu repeats. Numerous variants of GPA and GPB usually detected by abnormal expression of the blood group MNSs antigens are known. An increasing number of these variants have been structurally defined by protein and molecular genetic analyses, and have been shown to result from point mutations, gene deletions, hybrid gene fusion products generated by unequal crossing-over (not at Alu repeats), and microconversion events. The second group of RBC membrane glycophorins includes the minor proteins GPC and GPD both of which carry blood group Gerbich antigens. Protein and nucleic acid analysis indicated that GPD is a truncated form of GPC in its N-terminal region, and that both proteins are produced by a unique gene called GE (Gerbich), which is present as a single copy per haploid genome and is located on chromosome 2q14-q21.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemistry and molecular biology of MNSs blood group antigens

This chapter has reviewed the nature of antigens of the MNSs blood group system. The structures of the proteins and the molecular features and organization of glycophorin genes were described, emphasizing their domain arrangement and the extensive sequence homology that indicates that their common and variant alleles belong to a single gene family. Methods currently used to examine these antigens are immunoblotting and DNA typing. The majority of variant genes are hybrids of parent glycophorin genes in a variety of arrangements; they contain no other sequences but those of the parent genes. The structures of the hybrids are summarized in Figure 8. Several hybrids appear to have arisen by unequal homologous recombination but others appear to have occurred through gene conversion. In this system the molecular genetic basis for a single variant phenotype may differ, as documented by gene rearrangements that appear to have occurred, as separate events, at different sites in the same intron; this has resulted in protein structures (hence phenotypes) that are identical. For example, unequal homologous recombination occurring within intron 3 can have given rise to only a limited number of phenotypes, namely alpha M-delta S, alpha N-delta S, alpha M-delta S, alpha N-delta S and delta-alpha. In addition, different sites of an exon may have been involved in gene rearrangements through gene conversion leading to nearly identical protein structures, yet different serological phenotypes. Thus, gene conversion could be more significant for generation of antigenic diversification as the number of possible new alleles is quite large. The participation of the HGpE gene in these rearrangements would make this number even larger. New sites and the expressed pseudoexon have created the epitopes of the variant phenotypes, and sequences specific for several variant antisera have been identified. Thus, the molecular basis for several serological reactions involving this system is now better understood.

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.

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.

Molecular analysis of glycophorin A and B gene structure and expression in homozygous Miltenberger class V (Mi. V) human erythrocytes

In the Miltenberger class V (Mi. V) condition, red cells lack glycophorin A (GPA) and glycophorin B (GPB) but carry instead an unusual glycoprotein thought to be a hybrid molecule produced by the unequal crossing-over between the closely linked genes encoding for GPA and GPB. By Western blot analysis with rabbit anti-GPA antibodies specific for discrete domains of GPA, it was found that the Mi. V glycoprotein (donor F. M.) contains approximately 60 amino acid residues of GPA at its N-terminus. As a preliminary approach to the molecular analysis of this variant the restriction maps of the GPA and GPB genes were established by Southern blot analysis of genomic DNA and from genomic clones isolated from a human leukocyte library constructed in lambda EMBL4. The GPA and GPB genes cover about 30 kb of DNA and are organized into seven exons (A-1-A-7) and five exons (B-1-B-5), respectively. In addition to the normal genes, a third gene (named inv), closely resembling the GPA and GPB genes, was also identified. In the homozygous Mi. V individual the normal GPA and GPB genes were absent, but an unusual form of gene structure was detected by Southern blot analysis. The Mi. V glycoprotein gene was composed of exon B-1 of the GPB gene followed by exons A-2 and A-3 of the GPA gene and the exons B-3, B-4 and B-5 of the GPB gene. Exon B-1 can be distinguished from exon A-1 of GPA since it is located within a different restriction fragment, but both encode the same amino acid sequence (N-terminal region of the signal peptides). Using the polymerase chain reaction, the junction between exon A-3 and exon B-3 was confirmed by amplification of the DNA region where the putative crossing-over has occurred and it was deduced that the Mi. V glycoprotein is a hybrid molecule composed of amino acid residues 1-58 from GPA fused to amino acid residues 27-72 of GPB. In addition, the finding that part of the signal peptide and the 5'-untranslated region are derived from GPB suggests that the genetic background of the Mi. V variant is rather complex and may involve a cascade of recombination or gene conversion events.

A novel variety of the Dantu gene complex (DantuMD) detected in a Caucasian

The first Caucasian (MD) shown to exhibit the low-frequency MNSs system antigen, Dantu was detected due to an increased tendency of erythrocytes to be aggregated by substances that promote red cell agglutination. The donor was found to exhibit a novel variety of the Dantu gene complex (DantuMD), as judged from biochemical, immunochemical, and serological studies. The glycophorin (GP) A level of MD's erythrocyte membranes were slightly decreased (about 17%) but GP B was not significantly different from normal. GP A and GP B of MD's cells were shown to carry M and N or S and s antigens, respectively, indicating that MD exhibits two genes encoding GP A and two genes encoding GP B. MD's cells contain a Dantu-, N- and s-specific GP B-GP A hybrid GP (molar ratio to GP A approx. 0.6:1.0). Partial amino-acid sequence analysis indicates that the structure of this molecule is rather similar to, or completely identical with, that of the hybrid GP in DantuNE erythrocytes. The residues 1-39 or 40-99 of the latter molecule correspond to the residues 1-39 of s-specific GP B and the residues 72-131 of GP A, respectively. Statistical evidence suggests that MD exhibits a single gene encoding the hybrid GP. Thus, MD appears to be heterozygous for a typical anti-Lepore type gene complex that seems to comprise genes for GP A, GP B, and the GP B-GP A hybrid. The diminished GP A level and a decreased galactose-oxidase labelling of the major membrane protein (anion channel protein, band 3) in MD's cells is in accordance with previous data suggesting that band 3 might form a complex with GP A and the Dantu-specific hybrid GP. This complex formation may be necessary for optimum incorporation of the latter molecules into the membrane.

Evidence for increased in vivo mutation and somatic recombination in Bloom's syndrome

The glycophorin A assay was used to estimate the frequency of mutations that accumulate in vivo in somatic cells of persons with Bloom's syndrome (BS). This assay measures the frequency in persons of blood type MN of variant erythrocytes that lack the expression of one allelic form of glycophorin A, presumably due to mutational or recombinational events in erythroid precursor cells. Samples of blood from persons with BS showed dramatic 50- to 100-fold increases in the frequency of variants of three types, those with a hemizygous phenotype, those with a homozygous phenotype, and those with what appears to be partial loss of the expression of one locus. The high frequency of homozygous variants, genetic evidence for altered allelic segregation of a specific biochemical locus, provides evidence for increased somatic crossing-over in vivo in BS. An increased generation of functional hemizygosity and homozygosity in their somatic cells may play an important role in the extreme cancer risk of persons with BS.

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.

Characterization of a genomic hybrid specifying the human erythrocyte antigen Dantu: Dantu gene is duplicated and linked to a delta glycophorin gene deletion

Dantu is a rare antigen of the human MNSs blood group system carried by a hybrid glycophorin on the erythrocyte membrane. To delineate its structure and relationship to alpha and delta glycophorins at the genomic level, we analyzed DNA from a three-generation family, in which both the presence of Dantu and Mi-III (another rare MNSs antigen) and the absence of delta glycophorin were seen. Three gross alterations in the gene cluster correlated with the observed phenotypes. Differential hybridization, secondary restriction analysis, and sequence-specific oligonucleotide probing established that Dantu glycophorin is encoded by a distinct hybrid gene derived from fusion of delta and alpha genes. The junction point of the Dantu gene was assigned to the region spanning codons 31-39 of delta and codons 72-79 of alpha genes. Dosage quantitation suggested that Dantu gene is duplicated and tandemly arranged. Identification of delta gene deletion disclosed the molecular basis for the absence of delta glycophorin in two Dantu and Mi-III double heterozygotes. The DNA inheritance pattern together with DNA typing of MN blood groups verified the genotypes and established that the duplicated Dantu hybrid gene is linked to alpha M gene as well as a delta gene deletion. The origin of such a haplotype in a segment of Black population would require two recombination events via either unequal homologous crossing-over or gene conversion.

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.

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.