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Trimer Interface (trimer + interface)
Selected AbstractsStructures of vaccinia virus dUTPase and its nucleotide complexesACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2007Alexandra Samal Deoxyuridine triphosphate nucleotidohydrolase (dUTPase) catalyzes the hydrolysis of dUTP to dUMP and pyrophosphate in the presence of Mg2+ ions. The enzyme plays multiple cellular roles by maintaining a low dUTP:dTTP ratio and by synthesizing the substrate for thymidylate synthase in the biosynthesis of dTTP. Although dUTPase is an essential enzyme and has been established as a valid target for drug design, the high degree of homology of vaccinia virus dUTPase to the human enzyme makes the identification of selective inhibitors difficult. The crystal structure of vaccinia virus dUTPase has been solved and the active site has been mapped by crystallographic analysis of the apo enzyme and of complexes with the substrate-analog dUMPNPP, with the product dUMP and with dUDP, which acts as an inhibitor. Analyses of these structures reveal subtle differences between the viral and human enzymes. In particular, the much larger size of the central channel at the trimer interface suggests new possibilities for structure-based drug design. Vaccinia virus is a prototype of the poxviruses. [source] Structure of serine acetyltransferase from Haemophilus influenzae RdACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2004Jason Gorman The crystal structure of serine acetyltransferase (SAT) from Haemophilus influenzae Rd determined at 2.7,Å resolution is presented. SAT is a member of a family of hexapeptide-containing transferases that contain six-residue tandem repeats (LIV)-G- X4 that have been shown to form left-handed parallel ,-helices. In the current structure, each protomer is comprised of two domains: an N-terminal ,-helical domain and a C-terminal left-handed parallel ,-helix domain. Although other members of this protein family are known to form trimeric structures, SAT forms a dimer of trimers in which the trimer interface is mediated through interactions between both the ,-helix domains and N-terminal domains; these trimers dimerize through contacts in the N-terminal domain. All dimer-of-trimer interactions are mediated through amino acids within an N-terminal extension common only to a subset of SATs, suggesting that members of this subfamily may also adopt hexameric structures. Putative active sites are formed by crevices between adjacent protomers in a trimer. Thus, six independent active sites exist in the hexameric enzyme complex. [source] A double mutation of Escherichia coli 2C -methyl- d -erythritol-2,4-cyclodiphosphate synthase disrupts six hydrogen bonds with, yet fails to prevent binding of, an isoprenoid diphosphateACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 7 2005Tanja Sgraja The essential enzyme 2C -methyl- d -erythritol-2,4-cyclodiphosphate (MECP) synthase, found in most eubacteria and the apicomplexan parasites, participates in isoprenoid-precursor biosynthesis and is a validated target for the development of broad-spectrum antimicrobial drugs. The structure and mechanism of the enzyme have been elucidated and the recent exciting finding that the enzyme actually binds diphosphate-containing isoprenoids at the interface formed by the three subunits that constitute the active protein suggests the possibility of feedback regulation of MECP synthase. To investigate such a possibility, a form of the enzyme was sought that did not bind these ligands but which would retain the quaternary structure necessary to create the active site. Two amino acids, Arg142 and Glu144, in Escherichia coli MECP synthase were identified as contributing to ligand binding. Glu144 interacts directly with Arg142 and positions the basic residue to form two hydrogen bonds with the terminal phosphate group of the isoprenoid diphosphate ligand. This association occurs at the trimer interface and three of these arginines interact with the ligand phosphate group. A dual mutation was designed (Arg142 to methionine and Glu144 to leucine) to disrupt the electrostatic attractions between the enzyme and the phosphate group to investigate whether an enzyme without isoprenoid diphosphate could be obtained. A low-resolution crystal structure of the mutated MECP synthase Met142/Leu144 revealed that geranyl diphosphate was retained despite the removal of six hydrogen bonds normally formed with the enzyme. This indicates that these two hydrophilic residues on the surface of the enzyme are not major determinants of isoprenoid binding at the trimer interface but rather that hydrophobic interactions between the hydrocarbon tail and the core of the enzyme trimer dominate ligand binding. [source] Cloning, crystallization and preliminary X-ray studies of XC2981 from Xanthomonas campestris, a putative CutA1 protein involved in copper-ion homeostasisACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 11 2006Chien-Hung Lin Divalent metal ions play key roles in all living organisms, serving as cofactors for many proteins involved in a variety of electron-transfer activities. However, copper ions are highly toxic when an excessive amount is accumulated in a cell. CutA1 is a protein found in all kingdoms of life that is believed to participate in copper-ion tolerance in Escherichia coli, although its specific function remains unknown. Several crystal structures of multimeric CutA1 with different rotation angles and degrees of interaction between trimer interfaces have been reported. Here, the cloning, expression, crystallization and preliminary X-ray analysis of XC2981, a possible CutA1 protein present in the plant pathogen Xanthomonas campestris, are reported. The XC2981 crystals diffracted to a resolution of 2.6,Å. They are cubic and belong to space group I23, with unit-cell parameters a = b = c = 130.73,Å. [source] | ||||||||||