Biomedical subjects

M J Tanner

Publications and source records attributed to M J Tanner.

At least 55 records · Page 3Linked to original sources

PubMed1995

Band 3 Chur: a variant associated with band 3-deficient hereditary spherocytosis and substitution in a highly conserved position of transmembrane segment 11.

We studied a large Swiss family with dominantly inherited hereditary spherocytosis and band 3 (anion exchanger 1, AE1) deficiency. Band 3 cDNA was analysed by single-strand conformation polymorphism analysis and nucleotide sequencing. A new point mutation was found: G771D (GGC-->GAC). This change was present in all eight investigated patients but absent in four healthy members of the family. It is located at a highly conserved position in the middle of transmembrane segment 11, introducing a negative charge in a stretch of 16 apolar or neutral residues. None of the six amino-acid substitutions already known in this region as being associated with band 3 deficiency were recorded. To rule out any major transcriptional or post-transcriptional defect, we evaluated the amount of band 3 mRNA by RNase mapping using a band 3-protein 4.1 chimaeric probe. Similar mRNA amounts were present in patients and controls. Our results strengthen the view that some amino-acids, that are well conserved throughout the AE family, may be crucial for the insertion and/or the stabilization of band 3 within the lipid bilayer. At the present time, most of the mutations altering such residues are located in the C-terminal region of band 3.

Animals↗

PubMed1995

A point mutation in the protein 4.2 gene (allele 4.2 Tozeur) associated with hereditary haemolytic anaemia.

A recessively transmitted haemolytic anaemia associated with the lack of protein 4.2 was found in a Tunisian kindred. Trace amounts of this protein (72 kD component) became visible using high-sensitivity Western blots. Band 3 and ankyrin genes were excluded as candidate genes by linkage studies, and nucleotide sequencing of band 3 cytoplasmic domain cDNA revealed no alteration. In contrast, protein 4.2 gene contained in the homozygous state a mutation at position 310: CGA-->CAA (Arg-->Gln). This mutation defining allele 4.2 Tozeur was co-inherited with the disease. The mRNA encoding the variant protein was normal in size and approximately normal in amount. Recombinant protein 4.2 Tozeur bound normally to red cell IOVs but disclosed an increased susceptibility to proteolysis in vitro. We infer that the nearly total absence of protein 4.2 in the patients results from imbalance between destruction and synthesis of mutated protein 4.2 prior to its binding to the membrane.

Anemia, Hemolytic↗

PubMed1994

Isolation and characterization of CD47 glycoprotein: a multispanning membrane protein which is the same as integrin-associated protein (IAP) and the ovarian tumour marker OA3.

The CD47 glycoprotein was isolated from human erythrocytes by immunoprecipitation using monoclonal antibody (mAb) BRIC-125. Enzymic deglycosylation of the protein showed it contained N-linked oligosaccharides, and trypsin proteolysis of the protein in situ in the erythrocyte membrane cleaved it into two portions, one of which was glycosylated. Both the intact protein and the glycosylated fragment had blocked N-termini. Amino acid sequence was obtained from several proteolytic fragments of CD47. Comparison with the sequence database showed the protein to be very similar to or identical with OA3, a multispanning membrane protein. The protein also appears to be the same as the integrin-associated protein, which has a role in cell adhesion in non-erythroid cells. CD47 has six potential N-glycosylation sites, five of which are in an Ig superfamily domain. We show that three of these sites carry N-glycans in erythrocytes. Immunocytochemical staining of human tissues showed that CD47 was broadly distributed on mesenchyme and epithelia at multiple sites. Reactivity was particularly prominent in surface and ductular epithelia, and in the brain. The possible roles of the CD47 glycoprotein are discussed.

Amino Acid Sequence↗

PubMed1994

The structure of the human red blood cell anion exchanger (EPB3, AE1, band 3) gene.

The structure and sequence of the human red blood cell anion exchanger (EPB3, AE1, band 3) gene was determined by analysis of genomic and cDNA clones. The gene extends over 18 kb and consists of 20 exons. The cDNA sequence comprises 4,906 nucleotides [excluding the poly(A) tail]. There is extensive similarity between the human and mouse AE1 gene, although the latter covers 17 kb. The additional sequence present within the human AE1 gene compared with the mouse gene is mainly caused by the presence of 6 Alu repetitive units in the human gene between intron 13 and exon 20, one of which is within the 3' noncoding region of the cDNA. Two potential promoter regions within the human AE1 gene are located so that they could give rise to the different transcripts found in erythroid cells and in the kidney. The kidney transcript would lack exons 1 through 3 of the erythroid transcript. The translation initiator downstream to the human kidney promoter would give rise to a protein with a 20 amino acid section at the N-terminus that is not present in the erythroid human AE1 protein or the rodent kidney AE1 proteins.

Amino Acid Sequence↗

PubMed1994

Molecular basis of reduced or absent expression of decay-accelerating factor in Cromer blood group phenotypes.

The human erythrocyte blood group system Cromer consists of high-incidence and low-incidence antigens that reside on decay-accelerating factor (DAF; CD55), a glycosyl-phosphatidylinositol-anchored membrane protein that regulates complement activation on cell surfaces. In the Cromer phenotypes Dr(a-) and Inab there is reduced or absent expression of DAF, respectively. This study investigated the molecular basis of the reduced DAF expression by polymerase chain reaction amplification of genomic DNA and RNA/cDNA obtained from Epstein-Barr virus-transformed lymphoblastoid cell lines. Sequence analysis of the Inab propositus showed a single nucleotide substitution in exon 2 of the DAF gene and at the corresponding position in the cDNA, G314-->A resulting in Trp53-->Stop. This truncation near the amino terminus explains the complete absence of surface DAF in the Inab phenotype. A similar analysis was performed for two Dr(a-) individuals, including KZ, who was previously reported to be Inab phenotype but is now shown by immunochemical and serologic methods to be Dr(a-) phenotype. A single nucleotide change was found in exon 5 of the DAF gene, C649-->T resulting in Ser165-->Leu, which we had previously shown to lead to loss of the Dra epitope. However, two species of cDNA were found, one encoding full-length DAF with the single amino acid change and the more abundant species having a 44-nucleotide deletion. The 44 nucleotide deletion includes the single polymorphic site, which creates a cryptic branch point in the Dr(a-) allele that leads to use of a downstream cryptic acceptor splice site. This shifts the reading frame and leads to a premature stop codon that precludes membrane anchoring. Thus, the single point mutation in the Dr(a-) phenotype results in a novel use of alternative splicing and provides a molecular explanation for both the antigenicity and the reduced DAF expression seen in this phenotype.

Amino Acid Sequence↗

PubMed1994

Altered band 3 structure and function in glycophorin A- and B-deficient (MkMk) red blood cells.

The anion transport activity of the human erythrocyte anion transporter (band 3; AE1) has been examined in both normal and glycophorin A (GPA)-deficient (MkMk) human red blood cells (RBCs). The sulfate transport activity of MkMk cells (from two ethnically diverse sources) was approximately 60% that of normal erythrocytes under the transport assay conditions used. However, MkMk and normal RBCs contained similar amounts of band 3. The reduction in sulfate transport activity was shown to be caused by an increase in the apparent Km for sulfate in MkMk RBCs, suggesting the band 3 in the MkMk RBCs has a lowered binding affinity for sulfate anions. The size of the N-glycan chain on band 3 of the MkMk cells was larger than that on band 3 from normal RBCs. In contrast, the size of the N-glycan chain on the glucose transporter (GLUT1) from MkMk cells was smaller than that on GLUT1 from normal cells. The possible role of GPA in the biosynthesis and anion transport activity of band 3 in normal RBCs is discussed.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1994

Regulation of System B0 amino-acid-transport activity in the renal epithelial cell line NBL-1 and concomitant changes in SAAT1 hybridizing transcripts.

alpha-(Methylamino)isobutyric acid (MeAIB) insensitive Na(+)-dependent alanine transport activity in the bovine kidney cell line NBL-1 was increased upon amino acid starvation (> or = 20% over control levels). When L-phenylalanine (3 mM) was included in the starvation medium the increase was further enhanced (> or = 85% over control levels). In cells grown in control medium the Vmax, for MeAIB-insensitive Na+/alanine co-transport was found to be 6.0 +/- 0.7 nmol/3 min per mg (Km 41 +/- 12 microM) and for L-phenylalanine-treated amino-acid-starved cells the Vmax. was 21 +/- 5 nmol/3 min per mg (Km 92 +/- 40 microM). The increase in Vmax. was prevented by cycloheximide. Substrate specificity analysis identified the L-phenylalanine-induced transport system as System B0. [35S]Methionine labelling of cells during the amino acid starvation/phenylalanine treatments resulted in the differential labelling of a protein of 78 kDa. Northern-blot analysis using a SAAT1-specific probe revealed the presence of a new transcript (3.2 kb) in RNA extracted from cells incubated in amino acid starvation medium with L-phenylalanine included. The present findings suggest a novel means of control for System B0 by the use of physiological stress. It is also proposed that SAAT1 and System-B0 transcripts have considerable sequence similarity.

Alanine↗

PubMed1994

Band 3 Memphis variant II. Altered stilbene disulfonate binding and the Diego (Dia) blood group antigen are associated with the human erythrocyte band 3 mutation Pro854-->Leu.

Band 3 Memphis is a commonly occurring polymorphic form of the human red cell anion transporter (band 3, AE1). Band 3 Memphis migrates more slowly on an SDS-polyacrylamide gel than normal band 3 and results from a point mutation Lys56-->Glu. Two types of band 3 Memphis, variants I and II, can be distinguished by their susceptibility to covalent labeling with H2DIDS (4,4'-diisothiocyanato-2,2'-dihydrostilbene disulfonate). Memphis variant II is more readily labeled than Memphis variant I or normal band 3. The Memphis variant II is also associated with the presence of the Diego (Dia) blood group antigen on the red cells. We have shown that Memphis variant II carries the polymorphism Pro854-->Leu, as well as Lys56-->Glu. The blood group antigen (Dia) present at the surface of Memphis variant II type red cells suggests the mutation Pro854-->Leu causes a change in the structure of an extracellular loop of Memphis variant II band 3. We discuss possible ways in which the mutation Pro854-->Leu affects the reactivity of Lys539 to covalent reaction with H2DIDS.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1994

Localization of the protein 4.1-binding site on human erythrocyte glycophorins C and D.

The flexibility of the human erythrocyte membrane is mediated by an underlying network of skeletal proteins which interact with the membrane through ankyrin and protein 4.1. The nature of the membrane attachment site(s) for protein 4.1 has yet to be fully elucidated. In this paper we show that purified protein 4.1 binds much less strongly to alkali-stripped membranes from erythrocytes of individuals with total glycophorin C and D deficiency (Leach phenotype) than to alkali-stripped normal membranes. We further show that a synthetic peptide corresponding to amino acid residues 82-98 of the cytoplasmic domain of glycophorin C specifically binds to purified protein 4.1 and inhibits protein 4.1 binding to alkali-stripped normal membranes. The same synthetic peptide binds directly to membranes from individuals with glycophorin C and D deficiency but not to normal membranes. These results indicate that glycophorins C and D provide major membrane attachment sites for protein 4.1 in normal erythrocytes and that this interaction is mediated by protein 4.1 binding to amino acid residues 82-98 of glycophorin C and 61-77 of glycophorin D.

Amino Acid Sequence↗

PubMed1994

The solution structures of the first and second transmembrane-spanning segments of band 3.

We have studied the structures of synthetic peptides which correspond to the proposed first and second membrane-spanning segments of the human red cell anion transporter (band 3). The peptides, which were acetylated at their N-termini and amidated at the C-termini, comprise the 20 amino acids of residues 405-424 and 21 amino acids of residues 436-456 of the human band 3 sequence. The solution structures of the peptides in trifluoroethanol were studied by two-dimensional NMR spectroscopy. Characteristic NOEs were observed indicating that the peptides adopted a predominantly alpha-helical structure in trifluoroethanol solution. Dynamical simulated annealing using the program XPLOR was employed for the structure calculations. The amide exchange rates in trifluoroethanol have also been measured and are consistent with an alpha-helical structure for the peptides.

Acetylation↗

PubMed1994

Studies on the glycoprotein associated with Rh (rhesus) blood group antigen expression in the human red blood cell membrane.

The blood group Rh antigens are associated with non-glycosylated 30-kDa erythrocyte membrane proteins (the Rh30 polypeptides) and the Rh glycoprotein. We used antipeptide antibodies to study the Rh glycoprotein in human erythrocyte membranes. The Rh glycoprotein was present in Rhnull U+ve cells. However, the N-glycan chain of the Rh glycoprotein in Rhnull U+ve cells was smaller than in normal cells. In contrast, the N-glycan chain of the Rh glycoprotein was larger than normal in glycophorin B-deficient red cells. We suggest that this observation reflects a lower rate of movement of newly synthesized Rh glycoprotein through intracellular membranes to the cell surface in the absence of glycophorin B, and that in normal red cells glycophorin B facilitates the movement of the Rh protein complex to the cell surface. Our results provide evidence for the intracellular interaction of at least three proteins, the Rh glycoprotein, Rh30 polypeptides, and glycophorin B during the biosynthesis and cell surface expression of the Rh complex. These observations are likely to be important for the successful design of expression systems for the blood group Rh antigens.

Animals↗

PubMed1994

Topology and organization of human Rh (rhesus) blood group-related polypeptides.

The Rh blood group antigens are associated with nonglycosylated human erythrocyte membrane proteins of molecular mass 30 kDa (the Rh30 polypeptides) and a glycoprotein of 40-100 kDa (the Rh glycoprotein). We have studied the topology of this family of proteins in the erythrocyte membrane. We confirmed the predicted cytosolic localization of the C and N termini of the Rh protein family. We located Lys-196 and Arg-323 of the Rh glycoprotein to the cytosol, and Glu-34 to the extracellular side of the plasma membrane in erythrocytes, by N-terminal sequencing of Rh glycoprotein peptides produced by proteolysis at the cytoplasmic or extracellular side of the membrane. We also show that a glycan chain is present on only one (Asn-37) of the three potential N-glycan addition sites in the Rh glycoprotein. Studies of the Rh glycoprotein fragments that co-immunoprecipitated with the Rh30 polypeptides suggest there is an interaction between the Rh30 polypeptides and amino acids 35-196 of the Rh glycoprotein. A model for the organization of the components of the Rh complex in the red cell membrane is proposed.

Antibodies, Monoclonal↗

PubMed1994

The effects of glycophorin A on the expression of the human red cell anion transporter (band 3) in Xenopus oocytes.

The effects of human red cell glycophorin A (GPA) on the translocation to the plasma membrane and anion transport activity of the human erythrocyte anion transporter (band 3; AE1) have been examined using the Xenopus oocyte expression system. We show that band 3 accumulates steadily at the oocyte surface with time in the presence or absence of GPA, but this occurs more quickly when GPA is coexpressed. The amount of band 3 at the surface is determined by the concentrations of band 3 and GPA cRNA that are injected, with a higher proportion of total band 3 being translocated to the surface in the presence of GPA cRNA. The increased expression of DNDS-sensitive chloride transport is highly specific to GPA, and is not observed when the cRNA to the putative glycophorin E or a very high concentration of the cRNA to glycophorin C are coexpressed with band 3 in oocytes.

Animals↗

PubMed1993

The expression of the abnormal human red cell anion transporter from South-East Asian ovalocytes (band 3 SAO) in Xenopus oocytes.

South-East Asian ovalocytosis (SAO) is caused by the heterozygous presence of a variant form of the human erythrocyte anion transporter (band 3; AE1). The expression of band 3 SAO has been studied in Xenopus oocytes. Band 3 SAO is not functional as an anion transporter but is inserted stably into the plasma membrane of oocytes. Band 3 SAO translocation to the cell surface does not require co-expression of normal band 3. Co-expression of glycophorin A (GPA) increases the rate of translocation of band 3 SAO to the oocyte membrane but is not essential for this process. We suggest that the increased tendency of band 3 SAO to form oligomers may facilitate its translocation to the cell surface.

Animals↗

PubMed1993

Band 3 HT, a human red-cell variant associated with acanthocytosis and increased anion transport, carries the mutation Pro-868-->Leu in the membrane domain of band 3.

1. We have studied band 3 HT, a human red-cell band 3 variant with increased M(r), which is associated with abnormal red-cell shape (acanthocytosis) and increased anion-transport activity. 2. We have shown that the increased M(r) does not result from the presence of the band 3 Memphis mutation, and that the variant band 3 is covalently labelled by 4,4'-di-isothiocyanato-1,2-diphenylethane-2,2'-disulphonic acid (H2DIDS) less readily than normal. 3. cDNA cloning studies show that band 3 HT results from the mutation Pro-868-->Leu, and the possible significance of the mutation in the altered anion-transport activity and cytoskeleton binding properties of band 3 HT is discussed.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1993

A role for aminopeptidase N in Na(+)-dependent amino acid transport in bovine renal brush-border membranes.

A monoclonal antibody FD19 which removes reconstitutable Na(+)-dependent amino acid transport activity from solubilized bovine renal brush-border membrane vesicles was found to react specifically with the enzyme aminopeptidase N. Cleavage of aminopeptidase N from the membranes with papain inhibited Na(+)-dependent amino acid transport activity without affecting that of alpha-methyl D-glucoside. Removal of aminopeptidase substantially increased the Km values for the Na(+)-dependent transport of alanine, glutamine, leucine and phenylalanine without affecting the Vmax. Both Na(+)-dependent amino acid transport and aminopeptidase activity in intact vesicles were competitively inhibited by amino acids with very similar specificity. These results suggest that the amino acid-binding sites of aminopeptidase N and the transporter interact in some way to increase the Km of the transport process for its substrates. However, independent direct inactivation of the transport system by papain cannot be ruled out.

Alanine↗

PubMed1993

Identification of functioning regulatory sites and a new myosin binding site in the C-terminal 288 amino acids of caldesmon expressed from a human clone.

A partial clone of caldesmon, coding for the C-terminal 288 amino acids, was isolated from a human fetal liver cDNA library and sequenced. Expression of the clone in Escherichia coli produced a peptide called H1 (M(r) 32,549), which inhibited tropomyosin-enhanced actomyosin Mg(2+)-ATPase activity by 90% with half maximal inhibition at 0.03-0.04 mol H1 per mol actin. The inhibition could be reversed by Ca(2+)-calmodulin. H1 bound actin, Ca(2+)-calmodulin and tropomyosin and smooth muscle myosin with high affinities. This latter finding shows the presence of a second myosin-binding site in caldesmon. This was confirmed in thrombic digests of native sheep aorta and chicken gizzard caldesmon.

Actins↗

PubMed1993

The major integral proteins of the human red cell.

The structures and functions of the major human red cell integral membrane proteins are summarized in this review. The proteins that are discussed are the anion transporter (band 3), the sialic acid-rich glycophorins and the glucose transporter. Band 3 (AE1) is a member of a family of anion transporters which carry out Cl-/HCO3- exchange. AE1 is largely restricted to red cells and functions in CO2 transport between the tissues and lungs. In addition to its transport function band 3 acts as an anchor site to the membrane of the red cell skeleton, and also binds a number of cytoplasmic red cell proteins. Variant forms of band 3 are known and some of these have an effect on red cell function and viability. The glycophorins comprise three major proteins, glycophorin A (GPA), glycophorin B (GPB) and glycophorin C (GPC). GPA and GPB (together with another putative gene product, GPE) are closely related products of highly homologous genes located in tandem on the human chromosome. The similarity between the genes gives rise to a number of genetic variants as a result of unequal crossover events. The gene products are erythroid specific. The function of the proteins is not clearly established, but GPA appears to have a role in facilitating the movement of band 3 to the cell surface during the biosynthesis of the latter. The GPC gene is not related to the GPA, GPB and GPE gene family. This gene gives rise to GPC and a form of GPC which is truncated at the N-terminus and is designated GPD. GPC functions in anchoring the red cell skeleton to the membrane, and absence of the protein is associated with red cell abnormalities. GPC transcripts are found in many other tissues, where they probably also have a role in cytoskeletal interactions. The red cell glucose transporter (GLUT1) is a member of the gene family of passive glucose transporters. GLUT1 is not erythroid specific but is also present in several other tissues.

Amino Acid Sequence↗