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  • 1
    Electronic Resource
    Electronic Resource
    Bohr effect of Escherichia coli aspartate transcarbamylase. Linkages between substrate binding, proton binding, and conformational transitions (1979)
    s.l. : American Chemical Society
    Biochemistry 18 (1979), S. 3008-3015 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00581a016
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  • 2
    Electronic Resource
    Electronic Resource
    Preliminary Analysis of Amphibian Red Cell M Ferritin in a Novel Tetragonal Unit Cell (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 513-523 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The ferritins are a multigene family of proteins that concentrate and store iron in all prokaryotic and eukaryotic cells. 24 monomeric subunits which fold as four-helix bundles assemble to form a protein shell with 432 cubic symmetry and an external diameter of ∼130 Å. The iron is stored inside the protein shell as a mineralized core ∼80 Å in diameter. Recombinant amphibian red cell M ferritin crystallizes in ∼2 M (NH4)2SO4 at pH 4.6 in a space group that has not been reported previously. Electron microscopy, precession photography, Patterson and Fourier maps of the native protein and a UO{_2^{2+}} derivative, and simulations were used to determine that the unit-cell dimensions are a = b = 169.6, c = 481.2 Å, α = β = γ = 90° and the space group is P41212 or P43212. A preliminary model of the structure was obtained by molecular replacement, with amphibian red cell L ferritin as the model. In contrast to previously determined ferritin crystal structures which have intermolecular contacts at the twofold and threefold molecular axes, M ferritin crystals have a novel intermolecular interaction mediated by interdigitation of the DE loops of two molecules at the fourfold molecular axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444997003983
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  • 3
    Electronic Resource
    Electronic Resource
    Escherichia Coli Aspartate Transcarbamoylase: Structure, Energetics, and Catalytic and Regulatory Mechanisms (1989)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biophysics and Biomolecular Structure 18 (1989), S. 71-92 
    Details
    ISSN: 0084-6589
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.bb.18.060189.000443
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  • 4
    Electronic Resource
    Electronic Resource
    Equivalence of pairs of enantiomorphic space groups in the presence ofnon-crystallographic symmetry (1997)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 400-401 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The 11 pairs of enantiomorphic space groups with screw axes of opposite handedness generally can be distinguished when the asymmetric unit has known chirality. However, when the asymmetric unit has non-crystallographic rotational symmetry of the same fold or a multiple (in, where i is a positive integer) and the rotation axis is parallel to the screw axis, the screw axis reduces to a pure translational element. Under these circumstances, pairs of enantiomorphic space groups cannot be distinguished.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767397002705
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  • 5
    Electronic Resource
    Electronic Resource
    Crystal structure of bullfrog M ferritin at 2.8 Å resolution: analysis of subunit interactions and the binuclear metal center (1999)
    Springer
    JBIC 4 (1999), S. 243-256 
    Details
    ISSN: 1432-1327
    Keywords: Key words Crystallography ; Iron oxidation ; Iron storage ; Multisubunit proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Ferritins concentrate and store iron as a mineral in all bacterial, plant, and animal cells. The two ferritin subunit types, H or M (fast) and L (slow), differ in rates of iron uptake and mineralization and assemble in vivo to form heteropolymeric protein shells made up of 24 subunits; H/L subunit ratios reflect cell specificity of H and L subunit gene expression. A diferric peroxo species that is the initial reaction product of Fe(II) in H-type ferritins, as well as in ribonucleotide reductase (R2) and methane monooxygenase hydroxylase (MMOH), has recently been characterized, exploiting the relatively high accumulation of the peroxo intermediate in frog H-subunit type recombinant ferritin with the M sequence. The stability of the diferric reaction centers in R2 and MMOH contrasts with the instability of diferric centers in ferritin, which are precursors of the ferric mineral. We have determined the crystal structure of the homopolymer of recombinant frog M ferritin in two crystal forms: P41212, a=b=170.0 Å and c=481.5 Å; and P3121, a=b=210.8 Å and c=328.1 Å. The structural model for the trigonal form was refined to a crystallographic R value of 19.0% (R free=19.4%); the two structures have an r.m.s.d. of ∼ 0.22 Å for all Cα atoms. Comparison with the previously determined crystal structure of frog L ferritin indicates that the subunit interface at the molecular twofold axes is most variable, which may relate to the presence of the ferroxidase site in H-type ferritin subunits. Two metal ions (Mg) from the crystallization buffer were found in the ferroxidase site of the M ferritin crystals and interact with Glu23, Glu58, His61, Glu103, Gln137 and, unique to the M subunit, Asp140. The data suggest that Gln137 and Asp140 are a vestige of the second GluxxHis site, resulting from single nucleotide mutations of Glu and His codons and giving rise to Ala140 or Ser140 present in other eukaryotic H-type ferritins, by additional single nucleotide mutations. The observation of the Gln137xxAsp140 site in the frog M ferritin accounts for both the instability of the diferric oxy complexes in ferritin compared to MMOH and R2 and the observed kinetic variability of the diferric peroxo species in different H-type ferritin sequences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050310
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  • 6
    Electronic Resource
    Electronic Resource
    Identification of ‘private’ mutations in patients with ornithine transcarbamylase deficiency (1997)
    Springer
    Journal of inherited metabolic disease 20 (1997), S. 525-527 
    Details
    ISSN: 1573-2665
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The majority of cases of ornithine transcarbamylase deficiency are due to novel mutations making it impossible to develop common methods for genetic analysis. However, identification of causative mutations has important implications for diagnosis (particularly prenatal diagnosis), prediction of likely course and outcome and the eventual possibility of gene therapy. As part of a continuing study of ornithine transcarbamylase deficiency, we now report an additional thirty novel mutations in the ornithine transcarbamylase gene, together with a brief summary of their clinical presentations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005301513465
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  • 7
    Electronic Resource
    Electronic Resource
    The biochemical and molecular spectrum of ornithine transcarbamylase deficiency (1998)
    Springer
    Journal of inherited metabolic disease 21 (1998), S. 40-58 
    Details
    ISSN: 1573-2665
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Ornithine transcarbamylase (OTCase) deficiency, the most commoninherited urea cycle disorder, is transmitted as an X-linked trait. The clinical phenotype in affected males as well as heterozygous females shows a spectrum of severity ranging from neonatal hyperammonaemic coma to asymptomatic adults. The ornithine transcarbamylase enzyme is a trimer with three active sites per holoenzyme molecule, each of which is composed of an interdomain region of one polypeptide and a polar domain of the adjacent polypeptide. The OTC gene is located on the short arm of the X-chromosome and one of the two alleles undergoes inactivation in female cells. Approximately 140 mutations have been found in families affected with OTCase deficiency, most having their own 'private' mutation. Large deletions of one exon or more are seen in approximately 7% of patients, small deletions or insertions are seen in about 9%, and the remaining mutations are single base substitutions. Approximately 15% of mutations affect RNA splicing sites. The recurrent mutations are distributed equally among CpG dinucleotide hot spots. Generally, mutations causing neonatal disease affect amino acid residues that are 'buried' in the interior of the enzyme, especially around the active site, while those associated with late onset and milder phenotypes tend to be located on the surface of the protein. Very few mutations have been found in the sequence of the leader peptide, proportionally much fewer than in the sequence of the mature enzyme. Only few of the mutations have been expressed in bacteria or mammalian cells for the study of their deleterious mechanisms. Examples of expressed mutations include R277W and R277Q associated with late-onset disease, which markedly increase the Km for ornithine, shift the pH optimum to more alkaline and decrease the thermal stability of the purified mutant enzyme. R141Q (neonatal disease) disrupts the active site, whereas the purified R40H mutant has normal catalytic function and this mutation is likely to affect posttranslational processing such as mitochondrial targeting. It appears that most new mutations occur in male sperm and are then passed on to a transmitting heterozygous female. Uncommonly, mild mutations are transmitted by asymptomatic males to their daughters, subsequently resulting in clinical disease of males in future generations. The causes for variable expressivity of these mutations are currently unknown but are likely to involve a combination of environmental and genetic modifiers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005353407220
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  • 8
    Electronic Resource
    Electronic Resource
    Electrostatic interactions in the assembly of Escherichia coli aspartate transcarbamylase (1989)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 5 (1989), S. 66-77 
    Details
    ISSN: 0887-3585
    Keywords: subunit interactions ; allosteric regulation ; solvent accessibility ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Although ionizable groups are known to play important roles in the assembly, catalytic, and regulatory mechanisms of Escherichia coli aspartate transcarbamylase, these groups have not been characterized in detail. We report the application of static accessibility modified Tanford-Kirkwood theory to model electrostatic effects associated with the assembly of pair of chains, subunits, and the holoenzyme. All of the interchain interfaces except R1-R6 are stabilized by electrostatic interactions by -2 to -4 kcal-m-1 at pH 8. The pH dependence of the electrostatic component of the free energy of stabilization of intrasubunit contacts (C1-C2 and R1-R6) is qualitatively different from that of intersubunit contacts (C1-C4, C1-R1, and C1-R4). This difference may allow the transmission of information across subunit interfaces to be selectively regulated. Groups whose calculated pK or charge changes as a result of protein-protein interactions have been identified and the results correlated with available information about their function. Both the 240s loop of the c chain and the region near the Zn(II) ion of the r chain contain clusters of ionizable groups whose calculated pK values change by relatively large amounts upon assembly. These pK changes in turn extend to regions of the protein remote from the interface. The possibility that networks of ionizable groups are involved in transmitting information between binding sites is suggested.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340050108
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  • 9
    Electronic Resource
    Electronic Resource
    Crystallization and structural analysis of bullfrog red cell L-subunit ferritins (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 107-118 
    Details
    ISSN: 0887-3585
    Keywords: protein crystallography ; four helix bundle ; iron ; macromolecular assembly ; regulation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Ferritin is a 24 subunit protein that controls biomineralization of iron in animals, bacteria, and plants. Rates of mineralization vary among members of the ferritin family, particularly between L and H type subunits of animal ferritins which are differentially expressed in various cell types. To examine ferritin from a highly differentiated cell type and to clarify the relationship between ferritin structure and function, bullfrog red cell L ferritin has been cloned, overexpressed in E. coli, and crystallized under two conditions. Crystals were obtained at high ionic strength in the presence of MnCl2 at a concentration comparable to that of the protein and in the presence of MgCl2 at a concentration much higher than that of the protein. Under both crystallization conditions, the crystals are tetragonal bipyramids in the space group F432 with unit cell dimensions a=b=c= 182 ± 0.5 Å. Crystals obtained in the presence of manganese and ammonium sulfate diffract to 1.9 Å, while those obtained in the presence of magnesium and sodium tartrate diffract to 1.6 Å. Isomorphous crystals have been obtained under similar conditions for a site-directed mutant with a reduced mineralization rate in which Glu-57, -58, -59, and -61 are all replaced by Ala. The structure of wild type L-subunit with magnesium has been solved by molecular replacement using the calcium salt of human liver H subunit (Lawson et al., Nature (London) 349:541-544, 1991) as the model. The crystallographic R factor for the 6-2.2 Å shell is 0.21. The overall fold of human H and bullfrog L ferritins is similar with an rms difference in backbone atomic positions of 0.97 Å. The largest structural differences occur in the D helix and the loop connecting the D and E helices of the four helix bundle. Because red cell L ferritin and liver H ferritin show differences in both rates of mineralization and three-dimensional structure, more detailed comparisons of these structures are likely to shed new light on the relationship between conformation and function. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180204
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