Nicholas M Burton

University of Bristol, Bristol, England, United Kingdom

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Publications (23)124.52 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Kell is a complex blood group system comprising 35 antigens. Kell antigens are absent from rare red cells of the Ko (null) phenotype and expressed only weakly in the Kmod phenotype. Molecular analysis of three uncommon KEL alleles elucidated the obscure pattern of inheritance of Kell antigens in one family. Standard serological methods were employed. All exons, flanking intronic sequence and introns 15 and 16 of KEL were sequenced from genomic DNA. cDNA was obtained from erythroid cells cultured from progenitor cells isolated from peripheral blood. The Kmod propositus was heterozygous for two KEL mutations: c.2107G>A, p.Gly703Arg and a synonymous mutation, c.1719C>T, in the codon for p.573Gly. Sequencing of cDNA revealed that c.1719C>T caused skipping of exon 16, resulting in a silent allele. Her KEL:3,-4 brother was heterozygous for KEL*03/04 and c.1719C/T. A synonymous mutation caused complete exon skipping, despite being located 16 bases downstream of the 3′ splice site, resulting in a null KEL allele. The combined effects of two mod alleles, one responsible for KEL3 expression and the other for p.Gly703Arg, were probably responsible for an unexpected KEL:3,-4 phenotype.
    Vox Sanguinis 04/2014; 106(3):242-7. · 2.85 Impact Factor
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    ABSTRACT: The erythrocyte membrane has been extensively studied, both as a model membrane system and to investigate its role in gas exchange and transport. Much is now known about the protein components of the membrane, how they are organised into large multi-protein complexes and how they interact with each other within these complexes. Many links between the membrane and the cytoskeleton have also been delineated and have been demonstrated to be crucial for maintaining the deformability and integrity of the erythrocyte. In this study we have refined previous, highly speculative molecular models of these complexes by including the available data pertaining to known protein-protein interactions. While the refined models remain highly speculative, they provide an evolving framework for visualisation of these important cellular structures at the atomic level.
    Blood Cells Molecules and Diseases 03/2012; 49(1):1-10. · 2.26 Impact Factor
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    ABSTRACT: CYP164 family P450 enzymes are found in only a subset of mycobacteria and include CYP164A1, which is the sole P450 found in Mycobacterium leprae, the causative agent of leprosy. This has previously led to interest in this enzyme as a potential drug target. Here we describe the first crystal structure of a CYP164 enzyme, CYP164A2 from Mycobacterium smegmatis. CYP164A2 has a distinctive, enlarged hydrophobic active site that extends above the porphyrin ring toward the access channels. Unusually, we find that CYP164A2 can simultaneously bind two econazole molecules in different regions of the enlarged active site and is accompanied by the rearrangement and ordering of the BC loop. The primary location is through a classic interaction of the azole group with the porphyrin iron. The second econazole molecule is bound to a unique site and is linked to a tetracoordinated metal ion complexed to one of the heme carboxylates and to the side chains of His 105 and His 364. All of these features are preserved in the closely homologous M. leprae CYP164A1. The computational docking of azole compounds to a homology model of CYP164A1 suggests that these compounds will form effective inhibitors and is supported by the correlation of parallel docking with experimental binding studies of CYP164A2. The binding of econazole to CYP164A2 occurs primarily through the high-spin "open" conformation of the enzyme (K(d) [dissociation constant] of 0.1 μM), with binding to the low-spin "closed" form being significantly hindered (K(d) of 338 μM). These studies support previous suggestions that azole derivatives may provide an effective strategy to improve the treatment of leprosy.
    Antimicrobial Agents and Chemotherapy 01/2012; 56(1):391-402. · 4.57 Impact Factor
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    ABSTRACT: Many transcription factors control gene expression by binding to specific DNA sequences at or near the genes that they regulate. However, some transcription factors play more global roles in the control of gene expression by altering the architecture of sections of chromatin or even the whole genome. The ability to form oligomeric protein assemblies allows many of these proteins to manipulate extensive segments of DNA or chromatin via the formation of structures such as DNA loops or protein-DNA fibres. Here we show that the proline rich homeodomain protein PRH/Hhex forms predominantly octameric and/or hexadecameric species in solution as well as larger assemblies. We show that these assemblies are highly stable resisting denaturation by temperature and chemical denaturants. These data indicate that PRH is functionally and structurally related to the Lrp/AsnC family of proteins, a group of proteins that are known to act globally to control gene expression in bacteria and archaea.
    PLoS ONE 01/2012; 7(4):e35984. · 3.53 Impact Factor
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    ABSTRACT: Bacterial cell surfaces are commonly decorated with a layer formed from multiple copies of adhesin proteins whose binding interactions initiate colonization and infection processes. In this study, we investigate the physical deformability of the UspA1 adhesin protein from Moraxella catarrhalis, a causative agent of middle-ear infections in humans. UspA1 binds a range of extracellular proteins including fibronectin, and the epithelial cellular receptor carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1). Electron microscopy indicates that unliganded UspA1 is densely packed at, and extends about 800 Å from, the Moraxella surface. Using a modified atomic force microscope, we show that the adhesive properties and thickness of the UspA1 layer at the cell surface varies on addition of either fibronectin or CEACAM1. This in situ analysis is then correlated with the molecular structure of UspA1. To provide an overall model for UspA1, we have determined crystal structures for two N-terminal fragments which are then combined with a previous structure of the CEACAM1-binding site. We show that the UspA1-fibronectin complex is formed between UspA1 head region and the 13th type-III domain of fibronectin and, using X-ray scattering, that the complex involves an angular association between these two proteins. In combination with a previous study, which showed that the CEACAM1-UspA1 complex is distinctively bent in solution, we correlate these observations on isolated fragments of UspA1 with its in situ response on the cell surface. This study therefore provides a rare direct demonstration of protein conformational change at the cell surface.
    Proceedings of the National Academy of Sciences 08/2011; 108(37):15174-8. · 9.81 Impact Factor
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    ABSTRACT: The hereditary stomatocytoses are a series of dominantly inherited hemolytic anemias in which the permeability of the erythrocyte membrane to monovalent cations is pathologically increased. The causative mutations for some forms of hereditary stomatocytosis have been found in the transporter protein genes, RHAG and SLC4A1. Glucose transporter 1 (glut1) deficiency syndromes (glut1DSs) result from mutations in SLC2A1, encoding glut1. Glut1 is the main glucose transporter in the mammalian blood-brain barrier, and glut1DSs are manifested by an array of neurologic symptoms. We have previously reported 2 cases of stomatin-deficient cryohydrocytosis (sdCHC), a rare form of stomatocytosis associated with a cold-induced cation leak, hemolytic anemia, and hepatosplenomegaly but also with cataracts, seizures, mental retardation, and movement disorder. We now show that sdCHC is associated with mutations in SLC2A1 that cause both loss of glucose transport and a cation leak, as shown by expression studies in Xenopus oocytes. On the basis of a 3-dimensional model of glut1, we propose potential mechanisms underlying the phenotypes of the 2 mutations found. We investigated the loss of stomatin during erythropoiesis and find this occurs during reticulocyte maturation and involves endocytosis. The molecular basis of the glut1DS, paroxysmal exercise-induced dyskinesia, and sdCHC phenotypes are compared and discussed.
    Blood 07/2011; 118(19):5267-77. · 9.78 Impact Factor
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    ABSTRACT: Mutations in the human erythroid Krüppel-like factor (EKLF) can lead to either anemia or the benign InLu phenotype. To elucidate the relationship between these mutations and the differing phenotypes, we prepared recombinant forms of wild-type and 5 mutant EKLF proteins and quantitated their binding affinity to a range of EKLF-regulated genes. Missense mutants (R328H, R328L, and R331G) from persons with InLu phenotype did not bind DNA. Hence, as with the heterozygous loss of function nonsense (L127X, S270X, and K292X) and frameshift (P190Lfs and R319Efs) EKLF mutations, monoallelic loss of EKLF does not result in haploinsufficiency at all loci. In contrast, K332Q has a slightly reduced DNA binding affinity (∼ 2-fold) for all promoters examined but exhibits a phenotype only in a compound heterozygote with a nonfunctional allele. E325K also has a reduced, but significant, binding affinity, particularly for the β-globin gene but results in a disease phenotype even with the wild-type allele expressed, although not as a classic dominant-negative mutant. E325K protein may therefore actively interfere with EKLF-dependent processes by destabilizing transcription complexes, providing a rational explanation for the severity of the disease phenotype. Our study highlights the critical role of residues within the second EKLF zinc finger domain.
    Blood 07/2011; 118(11):3137-45. · 9.78 Impact Factor
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    Nicholas M Burton, Lesley J Bruce
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    ABSTRACT: The red cell membrane has long been the focus of extensive study. The macromolecules embedded within the membrane carry the blood group antigens and perform many functions including the vital task of gas exchange. Links between the intramembrane macromolecules and the underlying cytoskeleton stabilize the biconcave morphology of the red cell and allow deformation during microvascular transit. Much is now known about the proteins of the red cell membrane and how they are organised. In many cases we have an understanding of which proteins are expressed, the number of each protein per cell, their oligomeric state(s), and how they are collected in large multi-protein complexes. However, our typical view of these structures is as cartoon shapes in schematic figures. In this study we have combined knowledge of the red cell membrane with a wealth of protein structure data from crystallography, NMR, and homology modelling to generate the first, tentative models of the complexes which link the membrane to the cytoskeleton. Measurement of the size of these complexes and comparison with known cytoskeletal distance parameters suggests the idea of interaction between the membrane complexes, which may have profound implications for understanding red cell function and deformation.
    Biochemistry and Cell Biology 04/2011; 89(2):200-15. · 2.92 Impact Factor
  • Biophysical Journal 01/2011; 100(3). · 3.67 Impact Factor
  • N M Burton, G Daniels
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    ABSTRACT: The red cell surface membranes contain a large variety of proteins, many of which express blood group activity as a result of variation in their oligosaccharide or amino acid sequences. To understand the nature of the blood group epitopes, the functions of the proteins that express them and their relationship to each other, computer modelling has been employed to provide predictions of their structures. Modelling is an excellent method of first resort when experimental structural data for the protein of interest are absent or incomplete. The model can then be used to explain previous experimental data and to direct future experiments. In this review, examples of protein modelling are taken from the Rh, RHAG, Kell, LW, Lutheran, Duffy, Dombrock and RAPH blood group systems.
    Vox Sanguinis 01/2011; 100(1):129-39. · 2.85 Impact Factor
  • Transfusion Clinique Et Biologique - TRANSFUS CLIN BIOLOGIQUE. 01/2010; 17(3):201-201.
  • Transfusion Clinique Et Biologique - TRANSFUS CLIN BIOLOGIQUE. 01/2010; 17(3):203-204.
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    ABSTRACT: Rh-associated glycoprotein (RhAG) is closely associated with the Rh proteins in the red cell membrane. Two high frequency antigens (Duclos and DSLK) and one low frequency antigen (Ol(a)) have serological characteristics suggestive of expression on RhAG. RHAG was sequenced from the DNA of one Duclos-negative, one DSLK-negative, and two Ol(a+) individuals. Recombinant protein was expressed in HEK 293 cells. Protein models with RhAG subunits were constructed. The original Duclos-negative patient was homozygous for RHAG 316C>G, encoding Gln106Glu. HEK 293 cells expressing Gln106Glu mutant RhAG did not react with anti-Duclos. An individual with DSLK-negative red cells was homozygous for 490A>C, encoding Lys164Gln. Two Ol(a+) members of the original Norwegian family were heterozygous for 680C>T, encoding Ser227Leu. A Japanese donor with Rh(mod) phenotype had Ol(a+) red cells and was homozygous for 680C>T. The three red cell antigens encoded by RHAG form the RHAG blood group system: Duclos is RHAG1 (030001); Ol(a) is RHAG2 (030002); and DSLK is provisionally RHAG3 (030003).
    Vox Sanguinis 09/2009; 98(2):151-9. · 2.85 Impact Factor
  • Blood 01/2009; 114(22):72-72. · 9.78 Impact Factor
  • Nicholas M Burton, David J Anstee
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    ABSTRACT: The present article reviews recent data concerning the structure and function of the Rh-associated glycoprotein (RhAG) and considers what can be inferred about the structure and functional significance of the D and CE polypeptides. The structure of a bacterial RhAG (from Nitrosomonas europaea) has been solved and its gas channel elucidated. This information allows us to model a more accurate structure of RhD and RhCE polypeptides than has been possible hitherto. Human RhAG has been shown to act as a gas channel for CO2. Elucidation of the structure of a bacterial RhAG allows us to model the structure of D and CE polypeptides more accurately than before. Results suggest that whereas RhAG has a channel for passage of neutral gases (CO2, NH3 and possibly oxygen and nitric oxide), D and CE polypeptides are unlikely to have a transport function.
    Current opinion in hematology 12/2008; 15(6):625-30. · 5.19 Impact Factor
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    ABSTRACT: Overhydrated hereditary stomatocytosis (OHSt) is a rare dominantly inherited hemolytic anemia characterized by a profuse membrane leak to monovalent cations. Here, we show that OHSt red cell membranes contain slightly reduced amounts of Rh-associated glycoprotein (RhAG), a putative gas channel protein. DNA analysis revealed that the OHSt patients have 1 of 2 heterozygous mutations (t182g, t194c) in RHAG that lead to substitutions of 2 highly conserved amino acids (Ile61Arg, Phe65Ser). Unexpectedly, expression of wild-type RhAG in Xenopus laevis oocytes induced a monovalent cation leak; expression of the mutant RhAG proteins induced a leak about 6 times greater than that in wild type. RhAG belongs to the ammonium transporter family of proteins that form pore-like structures. We have modeled RhAG on the homologous Nitrosomonas europaea Rh50 protein and shown that these mutations are likely to lead to an opening of the pore. Although the function of RhAG remains controversial, this first report of functional RhAG mutations supports a role for RhAG as a cation pore.
    Blood 11/2008; 113(6):1350-7. · 9.78 Impact Factor
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    ABSTRACT: MER2 (RAPH1), the only antigen of the RAPH blood group system, is located on the tetraspanin CD151. Only four examples of alloanti-MER2 are known. We report here two new examples of alloanti-MER2, in women of Pakistani and Turkish origin, one of whom showed signs of a hemolytic transfusion reaction (HTR) after transfusion of 3 units of red cells (RBCs). Standard serologic methods were used. A monocyte monolayer assay (MMA) was used to assess the potential clinical significance of one of the antibodies. All exons and flanking intronic sequences of CD151 were amplified and sequenced. A homology model for CD151 second extracellular loop (EC2) was constructed based on the crystal structure of CD81. RBCs of both patients did not react with alloanti-MER2, and neither of their antibodies reacted with MER2-negative RBCs. The MMA results suggested that the antibody that appeared to have caused an HTR had the potential to be clinically significant. Both patients were homozygous for a 511C>T mutation in CD151 encoding an Arg171Cys change. This change did not result in any significant structural rearrangement in the protein model. Two MER2-negative patients with anti-MER2 are homozygous for the same novel mutation encoding an amino acid substitution in the EC2 of CD151. One of the antibodies may have been responsible for an HTR, and crossmatch-compatible RBCs should be recommended for transfusion to patients with anti-MER2.
    Transfusion 09/2008; 48(9):1912-6. · 3.53 Impact Factor
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    ABSTRACT: Moraxella catarrhalis is a ubiquitous human-specific bacterium commonly associated with upper and lower respiratory tract infections, including otitis media, sinusitis and chronic obstructive pulmonary disease. The bacterium uses an autotransporter protein UspA1 to target an important human cellular receptor carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1). Using X-ray crystallography, we show that the CEACAM1 receptor-binding region of UspA1 unusually consists of an extended, rod-like left-handed trimeric coiled-coil. Mutagenesis and binding studies of UspA1 and the N-domain of CEACAM1 have been used to delineate the interacting surfaces between ligand and receptor and guide assembly of the complex. However, solution scattering, molecular modelling and electron microscopy analyses all indicate that significant bending of the UspA1 coiled-coil stalk also occurs. This explains how UspA1 can engage CEACAM1 at a site far distant from its head group, permitting closer proximity of the respective cell surfaces during infection.
    The EMBO Journal 07/2008; 27(12):1779-89. · 9.82 Impact Factor
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    ABSTRACT: Comparison of normal erythroblasts and erythroblasts from persons with the rare In(Lu) type of Lu(a-b-) blood group phenotype showed increased transcription levels for 314 genes and reduced levels for 354 genes in In(Lu) cells. Many erythroid-specific genes (including ALAS2, SLC4A1) had reduced transcript levels, suggesting the phenotype resulted from a transcription factor abnormality. A search for mutations in erythroid transcription factors showed mutations in the promoter or coding sequence of EKLF in 21 of 24 persons with the In(Lu) phenotype. In all cases the mutant EKLF allele occurred in the presence of a normal EKLF allele. Nine different loss-of-function mutations were identified. One mutation abolished a GATA1 binding site in the EKLF promoter (-124T>C). Two mutations (Leu127X; Lys292X) resulted in premature termination codons, 2 (Pro190LeufsX47; Arg319GlufsX34) in frameshifts, and 4 in amino acid substitution of conserved residues in zinc finger domain 1 (His299Tyr) or domain 2 (Arg328Leu; Arg328His; Arg331Gly). Persons with the In(Lu) phenotype have no reported pathology, indicating that one functional EKLF allele is sufficient to sustain human erythropoiesis. These data provide the first description of inactivating mutations in human EKLF and the first demonstration of a blood group phenotype resulting from mutations in a transcription factor.
    Blood 05/2008; 112(5):2081-8. · 9.78 Impact Factor
  • Nicholas M Burton, R Leo Brady
    Blood Cells Molecules and Diseases 01/2008; 40(3):446-8. · 2.26 Impact Factor

Publication Stats

345 Citations
124.52 Total Impact Points

Institutions

  • 2009–2014
    • University of Bristol
      • School of Biochemistry
      Bristol, England, United Kingdom
  • 2012
    • Swansea University
      • Institute of Life Science "ILS"
      Swansea, Wales, United Kingdom
    • NHS Blood and Transplant
      Watford, England, United Kingdom
  • 2008
    • LifeShare Blood Centers
      Shreveport, Louisiana, United States
    • The Bracton Centre, Oxleas NHS Trust
      Дартфорде, England, United Kingdom