I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[6385]
Open Access
Abstract: Cellular stress in early mitosis activates the antephase checkpoint, resulting in the decondensation of chromosomes and delayed mitotic progression. Checkpoint with forkhead-associated and RING domains (CHFR) is central to this checkpoint, and its activity is ablated in many tumors and cancer cell lines through promoter hypermethylation or mutation. The interaction between the PAR-binding zinc finger (PBZ) of CHFR and poly(ADP-ribose) (PAR) is crucial for a functional antephase checkpoint. We determined the crystal structure of the cysteine-rich region of human CHFR (amino acids 425–664) to 1.9 Å resolution, which revealed a multizinc binding domain of elaborate topology within which the PBZ is embedded. The PBZ of CHFR closely resembles the analogous motifs from aprataxin-like factor and CG1218-PA, which lie within unstructured regions of their respective proteins. Based on co-crystal structures of CHFR bound to several different PAR-like ligands (adenosine 5′-diphosphoribose, adenosine monophosphate, and P1P2-diadenosine 5′-pyrophosphate), we made a model of the CHFR-PAR interaction, which we validated using site-specific mutagenesis and surface plasmon resonance. The PBZ motif of CHFR recognizes two adenine-containing subunits of PAR and the phosphate backbone that connects them. More generally, PBZ motifs may recognize different numbers of PAR subunits as required to carry out their functions.
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Dec 2010
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[1224]
Abstract: The Mycobacterium tuberculosis cytochrome P450 enzyme CYP142 is encoded in a large gene cluster involved in metabolism of host cholesterol. CYP142 was expressed and purified as a soluble, low spin P450 hemoprotein. CYP142 binds tightly to cholesterol and its oxidized derivative cholest-4-en-3-one, with extensive shift of the heme iron to the high spin state. High affinity for azole antibiotics was demonstrated, highlighting their therapeutic potential. CYP142 catalyzes either 27-hydroxylation of cholesterol/cholest-4-en-3-one or generates 5-cholestenoic acid/cholest-4-en-3-one-27-oic acid from these substrates by successive sterol oxidations, with the catalytic outcome dependent on the redox partner system used. The CYP142 crystal structure was solved to 1.6 Å, revealing a similar active site organization to the cholesterol-metabolizing M. tuberculosis CYP125, but having a near-identical organization of distal pocket residues to the branched fatty acid oxidizing M. tuberculosis CYP124. The cholesterol oxidizing activity of CYP142 provides an explanation for previous findings that ?CYP125 strains of Mycobacterium bovis and M. bovis BCG cannot grow on cholesterol, because these strains have a defective CYP142 gene. CYP142 is revealed as a cholesterol 27-oxidase with likely roles in host response modulation and cholesterol metabolism.
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Dec 2010
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I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[6388]
Abstract: Heme enzymes are ubiquitous in biology and catalyze a vast array of biological redox processes. The formation of high valent ferryl intermediates of the heme iron (known as Compounds I and Compound II) is implicated for a number of catalytic heme enzymes, but these species are formed only transiently and thus have proved somewhat elusive. In consequence, there has been conflicting evidence as to the nature of these ferryl intermediates in a number of different heme enzymes, in particular the precise nature of the bond between the heme iron and the bound oxygen atom. In this work, we present high resolution crystal structures of both Compound I and Compound II intermediates in two different heme peroxidase enzymes, cytochrome c peroxidase and ascorbate peroxidase, allowing direct and accurate comparison of the bonding interactions in the different intermediates. A consistent picture emerges across all structures, showing lengthening of the ferryl oxygen bond (and presumed protonation) on reduction of Compound I to Compound II. These data clarify long standing inconsistencies on the nature of the ferryl heme species in these intermediates.
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Jan 2011
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I03-Macromolecular Crystallography
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Dawei
Chen
,
Melanie
Vollmar
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Marianna N.
Rossi
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Claire
Phillips
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Rolf
Kraehenbuehl
,
Dea
Slade
,
Pawan V.
Mehrotra
,
Frank
Von Delft
,
Susan K.
Crosthwaite
,
Opher
Gileadi
,
John M.
Denu
,
Ivan
Ahel
Abstract: Sirtuins are a family of protein lysine deacetylases, which regulate gene silencing, metabolism, life span, and chromatin structure. Sirtuins utilize NAD+ to deacetylate proteins, yielding O-acetyl-ADP-ribose (OAADPr) as a reaction product. The macrodomain is a ubiquitous protein module known to bind ADP-ribose derivatives, which diverged through evolution to support many different protein functions and pathways. The observation that some sirtuins and macrodomains are physically linked as fusion proteins or genetically coupled through the same operon, provided a clue that their functions might be connected. Indeed, here we demonstrate that the product of the sirtuin reaction OAADPr is a substrate for several related macrodomain proteins: human MacroD1, human MacroD2, Escherichia coli YmdB, and the sirtuin-linked MacroD-like protein from Staphylococcus aureus. In addition, we show that the cell extracts derived from MacroD-deficient Neurospora crassa strain exhibit a major reduction in the ability to hydrolyze OAADPr. Our data support a novel function of macrodomains as OAADPr deacetylases and potential in vivo regulators of cellular OAADPr produced by NAD+-dependent deacetylation.
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Jan 2011
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Open Access
Abstract: The 57-residue small hydrophilic endoplasmic reticulum-associated protein (SHERP) shows highly specific, stage-regulated expression in the non-replicative vector-transmitted stages of the kinetoplastid parasite, Leishmania major, the causative agent of human cutaneous leishmaniasis. Previous studies have demonstrated that SHERP localizes as a peripheral membrane protein on the cytosolic face of the endoplasmic reticulum and on outer mitochondrial membranes, whereas its high copy number suggests a critical function in vivo. However, the absence of defined domains or identifiable orthologues, together with lack of a clear phenotype in transgenic parasites lacking SHERP, has limited functional understanding of this protein. Here, we use a combination of biophysical and biochemical methods to demonstrate that SHERP can be induced to adopt a globular fold in the presence of anionic lipids or SDS. Cross-linking and binding studies suggest that SHERP has the potential to form a complex with the vacuolar type H+-ATPase. Taken together, these results suggest that SHERP may function in modulating cellular processes related to membrane organization and/or acidification during vector transmission of infective Leishmania.
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Jan 2011
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[6386]
Abstract: Interfering intracellular antibodies are valuable for biological studies as drug surrogates and as potential macromolecular drugs per se. Their application is still limited because of the difficulty of acquisition of functional intracellular antibodies. We describe the use of the new intracellular antibody capture procedure (IAC3) to facilitate direct isolation of functional single domain antibody fragments using four independent target molecules (LMO2, TP53, CRAF1, and Hoxa9) from a set of diverse libraries. Initially, these have variability in only one of the three antigen-binding CDR regions of VH or VL and first round single domains are affinity matured by iterative randomization of the two other CDRs and reselection. We highlight the approach using a single domain binding to LMO2 protein. Our results show that interfering with LMO2 protein function demonstrates a role specifically in erythroid differentiation, confirm a necessary and sufficient function for LMO2 as a cancer therapy target in T-cell neoplasia and allowed for the first time production of soluble recombinant LMO2 protein by co-expression with intracellular domain antibodies. Co-crystallization of LMO2 and the anti-LMO2 VH protein was successful. These results demonstrate that this third generation IAC3 offers a robust toolbox for various biomedical applications and consolidates functional features of the LMO2 protein complex, which includes the importance of Lmo2-Ldb1 protein interaction.
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Jan 2011
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I03-Macromolecular Crystallography
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Morten
Nielsen
,
Michael
Suits
,
Min
Yang
,
Conor
Barry
,
Carlos
Martinez-fleites
,
Louise
Tailford
,
James
Flint
,
Claire
Dumon
,
Benjamin
Davis
,
Harry
Gilbert
,
Gideon
Davies
Abstract: The enzymatic transfer of the sugar mannose from activated sugar donors, is central to the synthesis of a wide range of biologically significant polysaccharides and glycoconjugates. In addition to their importance in cellular biology, mannosyltransferases also provide model systems with which to study catalytic mechanisms of glycosyltransfer. Mannosylglycerate synthase (MGS) catalyzes the synthesis of a-mannosyl-D-glycerate using GDP-mannose as the preferred donor species; a reaction that occurs with net retention of anomeric configuration. Past work has shown that the Rhodothermus marinus MGS, classified as a GT78 glycosyltransferase, displays a GT-A fold and performs catalysis in a metal-ion dependent manner. MGS shows very unusual metal-ion dependences with Mg2+, Ca2+and, to a varying extent, Mn2+, Ni2+, and Co2+, facilitating catalysis. Here, we probe these dependences through kinetic, and calorimetric analyses of wild-type and site-directed variants of the enzyme. Mutation of residues that interact with the guanine base of GDP are correlated with a higher kcat whilst substitution of H217, a key component of the metal-coordination site, results in a change in metal specificity to Mn2+. Structural analyses of MGS complexes not only provide insight into metal coordination but also into how lactate can function as an alternative acceptor to glycerate. These studies highlight the role of flexible loops in the active centre and the subsequent coordination of the divalent metal-ion as key factors in MGS catalysis and metal-ion dependence. Furthermore, Y220, located on a flexible loop whose conformation is likely influenced by metal binding also plays a critical role in substrate binding.
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Feb 2011
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I02-Macromolecular Crystallography
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Alan
Cartmell
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Lauren
Mckee
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Maria
Pena
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Johan
Larsbrink
,
Harry
Brumer
,
Satoshi
Kaneko
,
Hatomi
Ichinose
,
Rick
Lewis
,
Anders
Vikso-neilson
,
Harry
Gilbert
,
Jon
Marles-wright
Abstract: Reflecting the diverse chemistry of plant cell walls, microorganisms that degrade these composite structures synthesize an array of glycoside hydrolases. These enzymes are organized into sequence-, mechanism- and structure-based families. Genomic data has shown that several organisms that degrade the plant cell wall contain a large number of genes encoding family 43 (GH43) glycoside hydrolases. Here we report the biochemical properties of the GH43 enzymes of a saprophytic soil bacterium, Cellvibrio japonicus, and a human colonic symbiont, Bacteroides thetaiotaomicron. The data show that C. japonicus uses predominantly exo-acting enzymes to degrade arabinan into arabinose, while B. thetaiotaomicron deploys a combination of endo and side chain-cleaving glycoside hydrolases. Both organisms, however, utilize an arabinan-specific alpha-1,2-arabinofuranosidase in the degradative process, an activity that has not previously been reported. The enzyme can cleave alpha-1,2-arabinofuranose decorations in single or double substitutions, the latter being recalcitrant to the action of other arabinofuranosidases. The crystal structure of the C. japonicus arabinan-specific alpha-1,2-arabinofuranosidase, CjAbf43A displays a 5-bladed beta-propeller fold. The specificity of the enzyme for arabinan is conferred by a surface cleft that is complementary to the helical backbone of the polysaccharide. The specificity of CjAbf43A for alpha-1,2-L-arabinofuranose side chains is conferred by a polar residue that orientates the arabinan backbone such that O2 arabinose decorations are directed into the active site pocket. A shelf-like structure adjacent to the active site pocket accommodates O3 arabinose side chains, explaining how the enzyme can target O2 linkages that are components of single or double substitutions.
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Feb 2011
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I03-Macromolecular Crystallography
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Abstract: Homoprotocatechuate 2,3-dioxygenase from Brevibacterium fuscum (HPCD) has an Fe(II) center in its active site that can be replaced with Mn(II) or Co(II). Whereas Mn-HPCD exhibits steady-state kinetic parameters comparable to those of Fe-HPCD, Co-HPCD behaves somewhat differently, exhibiting significantly higher K\textM\textO 2 KMO2 and k cat. The high activity of Co-HPCD is surprising, given that cobalt has the highest standard M(III/II) redox potential of the three metals. Comparison of the X-ray crystal structures of the resting and substrate-bound forms of Fe-HPCD, Mn-HPCD, and Co-HPCD shows that metal substitution has no effect on the local ligand environment, the conformational integrity of the active site, or the overall protein structure, suggesting that the protein structure does not differentially tune the potential of the metal center. Analysis of the steady-state kinetics of Co-HPCD suggests that the Co(II) center alters the relative rate constants for the interconversion of intermediates in the catalytic cycle but still allows the dioxygenase reaction to proceed efficiently. When compared with the kinetic data for Fe-HPCD and Mn-HPCD, these results show that dioxygenase catalysis can proceed at high rates over a wide range of metal redox potentials. This is consistent with the proposed mechanism in which the metal mediates electron transfer between the catechol substrate and O2 to form the postulated [M(II)(semiquinone)superoxo] reactive species. These kinetic differences and the spectroscopic properties of Co-HPCD provide new tools with which to explore the unique O2 activation mechanism associated with the extradiol dioxygenase family.
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Feb 2011
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I02-Macromolecular Crystallography
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Ming
Yang
,
Wei
Ge
,
Rasheduzzaman
Chowdhury
,
Timothy
Claridge
,
Holger
Kramer
,
Bernhard
Schmierer
,
Michael A.
Mcdonough
,
Lingzhi
Gong
,
Benedikt
Kessler
,
Peter
Ratcliffe
,
Mathew
Coleman
,
Christopher
Schofield
Abstract: Cytoskeleton, Post-translational Modification, Protein Stability, Protein Structure, Proteomics, Ankyrin Repeat Domain, AnkyrinR, Factor Inhibiting HIF, Hydroxylation, Hypoxia-inducible Factor
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Mar 2011
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