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Extensive Interactions (extensive + interaction)
Selected AbstractsStructure of acostatin, a dimeric disintegrin from Southern copperhead (Agkistrodon contortrix contortrix), at 1.7,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2008Natalia Moiseeva Disintegrins are a family of small (4,14,kDa) proteins that bind to another class of proteins, integrins. Therefore, as integrin inhibitors, they can be exploited as anticancer and antiplatelet agents. Acostatin, an ,, heterodimeric disintegrin, has been isolated from the venom of Southern copperhead (Agkistrodon contortrix contortrix). The three-dimensional structure of acostatin has been determined by macromolecular crystallography using the molecular-replacement method. The asymmetric unit of the acostatin crystals consists of two heterodimers. The structure has been refined to an Rwork and Rfree of 18.6% and 21.5%, respectively, using all data in the 20,1.7,Å resolution range. The structure of all subunits is similar and is well ordered into N-terminal and C-terminal clusters with four intramolecular disulfide bonds. The overall fold consists of short ,-sheets, each of which is formed by a pair of antiparallel ,-strands connected by ,-turns and flexible loops of different lengths. Conformational flexibility is found in the RGD loops and in the C-terminal segment. The interaction of two N-terminal clusters via two intermolecular disulfide bridges anchors the ,, chains of the acostatin dimers. The C-terminal clusters of the heterodimer project in opposite directions and form a larger angle between them in comparison with other dimeric disintegrins. Extensive interactions are observed between two heterodimers, revealing an ,,,, acostatin tetramer. Further experiments are required to identify whether the ,,,, acostatin complex plays a functional role in vivo. [source] Unravelling control freakery: redefining central-local government relationsBRITISH JOURNAL OF POLITICS & INTERNATIONAL RELATIONS, Issue 3 2003David Wilson Central-local relations have been of particular interest since the Labour government came to power in 1997. Both academics and practitioners have pointed to tensions within the Labour government's reform agenda,between a ,top-down' and ,bottom-up' approach; between a drive for national standards and the encouragement of local learning and innovation; and between strengthening executive leadership and enhancing public participation. It is argued that while Labour's modernisation strategy has clear elements of a top-down approach (legislation, inspectorates, white papers, etc) there is also a significant bottom-up dimension (a variety of zones, experiments and pilots, albeit with different degrees of freedom). This article utilises a multi-level governance framework of analysis and argues that, while much of the research using such frameworks has hitherto focused on the EU, recent developments in governance at neighbourhood, local authority, sub-regional and regional levels facilitate its application within a nation state. The central thesis is that, while there is extensive interaction between actors at sub-national level, this should not be seen as a proxy for policy influence. The local political arena is characterised less by multi-level governance than by multi-level dialogue. Sub-national actors participate but they are rarely major players in shaping policy outcomes: the plurality which characterises sub-central governance does not reflect a pluralist power structure. [source] Effects of Water-Glycerol and Water-Sorbitol Interactions on the Physical Properties of Konjac Glucomannan FilmsJOURNAL OF FOOD SCIENCE, Issue 2 2006Lai Hoong Cheng ABSTRACT Konjac glucomannan (KGM)-edible films were prepared with different amounts of glycerol or sorbitol as a plasticizer. Films were characterized by moisture sorption isotherm, and following conditioning at different relative humidities, by differential scanning calorimetry and tensile tests. Moisture and polyols (sorbitol and glycerol) were found to plasticize KGM-based films with respect to their tensile properties. However, thermal properties and water sorption capacity (WSC) of polyolplasticized KGM films were found to vary with water activity (aw), namely at low aw (< 0.6), WSC and melting enthalpy were decreased with increasing in polyol content and the opposite was true at higher aw (>0.6). This was attributed to extensive interactions between plasticizer and KGM that reduced the available active site (-OH groups) for water adsorption. The presence of polyols at low aw appeared to suppress crystalline structures due probably to restricted molecular mobility. These effects were diminished when the moisture content was >20%. [source] Precursor complex structure of pseudouridine synthase TruB suggests coupling of active site perturbations to an RNA-sequestering peripheral protein domainPROTEIN SCIENCE, Issue 8 2005Charmaine Hoang Abstract The pseudouridine synthase TruB is responsible for the universally conserved post-transcriptional modification of residue 55 of elongator tRNAs. In addition to the active site, the "thumb," a peripheral domain unique to the TruB family of enzymes, makes extensive interactions with the substrate. To coordinate RNA binding and release with catalysis, the thumb may be able to sense progress of the reaction in the active site. To establish whether there is a structural correlate of communication between the active site and the RNA-sequestering thumb, we have solved the structure of a catalytically inactive point mutant of TruB in complex with a substrate RNA, and compared it to the previously determined structure of an active TruB bound to a reaction product. Superposition of the two structures shows that they are extremely similar, except in the active site and, intriguingly, in the relative position of the thumb. Because the two structures were solved using isomorphous crystals, and because the thumb is very well ordered in both structures, the displacement of the thumb we observe likely reflects preferential propagation of active site perturbations to this RNA-binding domain. One of the interactions between the active site and the thumb involves an active site residue whose hydrogen-bonding status changes during the reaction. This may allow the peripheral RNA-binding domain to monitor progress of the pseudouridylation reaction. [source] Structure of Arabidopsis chloroplastic monothiol glutaredoxin AtGRXcpACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2010Lenong Li Monothiol glutaredoxins (Grxs) play important roles in maintaining redox homeostasis in living cells and are conserved across species. Arabidopsis thaliana monothiol glutaredoxin AtGRXcp is critical for protection from oxidative stress in chloroplasts. The crystal structure of AtGRXcp has been determined at 2.4,Å resolution. AtGRXcp has a glutaredoxin/thioredoxin-like fold with distinct structural features that differ from those of dithiol Grxs. The structure reveals that the putative active-site motif CGFS is well defined and is located on the molecular surface and that a long groove extends to both sides of the catalytic Cys97. Structural comparison and molecular modeling suggest that glutathione can bind in this groove and form extensive interactions with conserved charged residues including Lys89, Arg126 and Asp152. Further comparative studies reveal that a unique loop with five additional residues adjacent to the active-site motif may be a key structural feature of monothiol Grxs and may influence their function. This study provides the first structural information on plant CGFS-type monothiol Grxs, allowing a better understanding of the redox-regulation mechanism mediated by these plant Grxs. [source] Structures of dihydrofolate reductase-thymidylate synthase of Trypanosoma cruzi in the folate-free state and in complex with two antifolate drugs, trimetrexate and methotrexateACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2009Olga Senkovich The flagellate protozoan parasite Trypanosoma cruzi is the pathogenic agent of Chagas disease (also called American trypanosomiasis), which causes approximately 50,000 deaths annually. The disease is endemic in South and Central America. The parasite is usually transmitted by a blood-feeding insect vector, but can also be transmitted via blood transfusion. In the chronic form, Chagas disease causes severe damage to the heart and other organs. There is no satisfactory treatment for chronic Chagas disease and no vaccine is available. There is an urgent need for the development of chemotherapeutic agents for the treatment of T. cruzi infection and therefore for the identification of potential drug targets. The dihydrofolate reductase activity of T. cruzi, which is expressed as part of a bifunctional enzyme, dihydrofolate reductase,thymidylate synthase (DHFR-TS), is a potential target for drug development. In order to gain a detailed understanding of the structure,function relationship of T. cruzi DHFR, the three-dimensional structure of this protein in complex with various ligands is being studied. Here, the crystal structures of T. cruzi DHFR-TS with three different compositions of the DHFR domain are reported: the folate-free state, the complex with the lipophilic antifolate trimetrexate (TMQ) and the complex with the classical antifolate methotrexate (MTX). These structures reveal that the enzyme is a homodimer with substantial interactions between the two TS domains of neighboring subunits. In contrast to the enzymes from Cryptosporidium hominis and Plasmodium falciparum, the DHFR and TS active sites of T. cruzi lie on the same side of the monomer. As in other parasitic DHFR-TS proteins, the N-terminal extension of the T. cruzi enzyme is involved in extensive interactions between the two domains. The DHFR active site of the T. cruzi enzyme shows subtle differences compared with its human counterpart. These differences may be exploited for the development of antifolate-based therapeutic agents for the treatment of T. cruzi infection. [source] Structure of Escherichia coli tryptophanaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2006Shao-Yang Ku Pyridoxal 5,-phosphate (PLP) dependent tryptophanase has been isolated from Escherichia coli and its crystal structure has been determined. The structure shares the same fold with and has similar quaternary structure to Proteus vulgaris tryptophanase and tyrosine-phenol lyase, but is found in a closed conformation when compared with these two enzymes. The tryptophanase structure, solved in its apo form, does not have covalent PLP bound in the active site, but two sulfate ions. The sulfate ions occupy the phosphoryl-binding site of PLP and the binding site of the ,-carboxyl of the natural substrate tryptophan. One of the sulfate ions makes extensive interactions with both the transferase and PLP-binding domains of the protein and appears to be responsible for holding the enzyme in its closed conformation. Based on the sulfate density and the structure of the P. vulgaris enzyme, PLP and the substrate tryptophan were modeled into the active site. The resulting model is consistent with the roles of Arg419 in orienting the substrate to PLP and acidifying the ,-proton of the substrate for ,-elimination, Lys269 in the formation and decomposition of the PLP quinonoid intermediate, Arg230 in orienting the substrate,PLP intermediates in the optimal conformation for catalysis, and His463 and Tyr74 in determining substrate specificity and suggests that the closed conformation observed in the structure could be induced by substrate binding and that significant conformational changes occur during catalysis. A catalytic mechanism for tryptophanase is proposed. Since E. coli tryptophanase has resisted forming diffraction-quality crystals for many years, the molecular surface of tryptophanase has been analyzed in various crystal forms and it was rationalized that strong crystal contacts occur on the flat surface of the protein and that the size of crystal contact surface seems to correlate with the diffraction quality of the crystal. 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