No description available.

Octa-heme cytochrome c tetrathionate reductase (OTR) from Shewanella oneidensis MR-1 is a periplasmic protein and shows several extraordinary structural features around its active-site heme. OTR has been found able to catalyse the in vitro reduction of tetrathionate, nitrite, hydroxylamine and hydrogen peroxide. However the physiological function of this novel protein remains unknown. The subject of this thesis is the in vitro catalytic mechanism and the in vivo function of OTR. As OTR displays great similarity with bacterial penta-heme cytochrome c nitrite reductase (NrfA) in several aspects, it has been proposed that OTR might be physiologically involved in the metabolism of nitrite or other nitrogenous compounds. However kinetics assays and phenotypes studies carried out in this project suggest this is not the case. In vitro kinetic assays of the reduction of nitrite and hydroxylamine catalysed by OTR showed no significant difference in enzyme activities among the wild-type OTR and its mutant forms which have one active site residue replaced by alanine, namely OTR K153A, C64A, N61A and D150A. And the nitrite reductase activity of OTR (kcat/Km = 1.0×105 M-1•s-1) are much lower than that of NrfA (kcat/Km = ~108 M-1•s-1). These results indicate that OTR is not specifically adapted to reduce nitrite and it cannot compete for nitrite against NrfA in vivo. No phenotype difference was identified between the wild-type and the Δotr strain of Shewanella oneidensis MR-1 when nitrite or nitrate served as the sole electron acceptor. OTR appears not to be involved in the respiration or detoxification of nitrite, which is consistent with previous transcriptional and phenotype reports that involve OTR or its homologues. The in vitro tetrathionate reduction activity of OTR was unable to be reproduced in this project for unknown reasons. Although transcriptomic data from the literature suggest that OTR may be related to the metabolism of sulphur-containing compounds, kinetic and phenotype studies reveal that OTR does not directly participate in the respiration of thiosulfate, sulfite, tetrathionate, polysulfide or elemental sulphur. Cysteine 64 is a highly-conserved amino acid residue of OTR close to the active site and its side-chain sulphur atom is covalently bonded by either an oxygen or a sulphur atom as observed in the crystal structure. Such a modification is potentially important to the function of OTR. ESI mass spectroscopy results show that in native OTR the modified form is around 48 Da heavier than the unmodified form, and the MALDITOF peptide mass spectra show that the modified form could be converted into the unmodified form by reducing agent DTT. These results suggest that the modification could be a cysteine persulfide attaching an extra oxygen atom in the form of water or hydroxide anion.

Abstract Today everyone have a lot of meetings. The meetings¡¦ efficiency is quite low and group decision-making quality is bad. In foreign, many methods have good effects on it. Open space technology is one of them. But it has some conditions and assumptions which don¡¦t fit our culture and the conditions of our companies. We have to improve Open space technology to draw its effects. We improve it according to our assumptions and principles. We also assist it with some technologies, like Talking stick, circling, and catalytic mechanism. They all have outstanding and stable results. They can help Open space technology to overcome the deficit of ideal conditions. This research¡¦s main point is to introduce and collect the creative ways of the improved Open space technology. In two hospitals, we can see the improved Open space technology which has obvious effects and promote the group decision-making quality a lot. It still can get good results under the deficit of ideal conditions. We conclude that it has 9 traits as followed: 1. It lowers the barrier of inertia. 2. Interactions 3. Positive feedback 4. Participation 5. The form of activity 6. Safety 7. Closer contact with others 8. Appreciative attitude 9. Truly contribution This research is a initial research and introduction of the improved Open space technology. We suggest other researchers can popularize the improved Open space technology and get the more generalization results.

No description available.

The major aim of this work has been to gain further insights into the catalytic mechanism of carbonic anhydrase (carbonate hydro-lyase, EC 4.2.1.1). One approach has been to replace the essential Zn(II) ion by Cd(II) which has favourable spectroscopic properties. The Cd(II)-enzymes have appreciable 4-nitrophenyl acetate hydrolase activities. These activities increase with pH as if dependent on the basic form of a group with pKa near 10. The Cd(II)-carbonic anhydrases also have significant carbon dioxide hydration activities. Jhe Cd(II) derivatives are strongly inhibited by monovalent anions. The 113-Cd(II) derivatives have also been studied by 113-Cd NMR as a function of pH and bicarbonate or inhibitor concentration. Plots of chemical shift versus pH give sigmoidal titration curves in the studied pH range, 10.3. The p«a values vary from 9.2 to 9.7 correlating reasonably well with the activity profiles. When bicarbonate is added to the samples the 113-Cd resonances shift upfield to new characteristic positions. The inhibitors CN", SH", and SCN” bind directly to the metal ion with their C, S, and N atoms, respectively. The results are best explained by assuming a rapid exchange between three species in which the open coordination site of the metal ion is occupied by'hydroxide, water, or bicarbonate. Another approach has been to study kinetic properties of the active en­zyme. A number of monovalent anions were investigated as inhibitors of carbon dioxide hydration catalyzed by human carbonic anhydrase II. Predominantly uncompetitive inhibition patterns were observed at pH near 9 in all cases. The inhibition of human carbonic anhydrase II by the organic compounds tetrazole, 1,2,4-triazole, 2-nitrophenol, and chloral hydrate was also investigated. These inhibitors, together with phenol, can be classified in three groups depending upon the kinetic patterns of inhibition of carbon dioixde hydration at pH near 9. The first group, represented by tetrazole and 2-nitrophenol, yields predominantly uncompetitive inhibition under these conditions in analogy with simple, inorganic anions. The second group, represented by 1,2,4-triazole and chloral hydrate gives rise to essentially noncompetitive inhibition patterns whereas phenol, representing the third group, is a competitive inhibitor of carbon dioxide hydration. These results are analyzed in terms of two rivaling mechanism models, a kinetic scheme originally proposed by Steiner et al. (Eur. 3. Biochem. (1975) 59, 253-259) and a rapid-equilibrium kinetic scheme proposed by Pocker and Deits (3. Am. Chem. Soc. (1982) 104, 2424-2434). It is concluded that the observed steady-state inhibition patterns are compatible with both models, but hat discriminatory data, strongly favouring the model of Stêiner et al., are available in the literature. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1984, härtill 4 uppsatser</p> / digitalisering@umu

La résistance bactérienne aux antibiotiques est un problème majeur de santé publique. Un moyen de la combattre est de viser des cibles non encore exploitées pour retarder l’apparition de la résistance. Dans ce contexte, nous avons entrepris la caractérisation sur les plans biochimique et structural de l’enzyme MraY, une protéine intégrale de membrane, membre d’une famille de transférases membranaires. MraY catalyse la première étape membranaire de la biosynthèse du peptidoglycane bactérien à savoir, le transfert du motif N-acétylmuramoyl-pentapeptide du précurseur cytoplasmique UDP-MurNAc-pentapeptide sur le transporteur membranaire, l’undécaprényl-phosphate aboutissant à la formation du lipide I. Aucune structure 3D de cette enzyme n’est disponible actuellement et aucun antibiotique en utilisation clinique ne la cible. D’une part nous avons entrepris la caractérisation structurale de cette enzyme par des approches de biophysique. Des essais de cristallisation 2D dans des systèmes membranaires ont permis d’observer au microscope électronique des dimères de MraY (taille de 70Å/50Å). Des expériences de diffusion des rayons X (SAXS) montrent un rayon de giration d’environ 42Å. Les résultats issus des expériences de SAXS ont été combinés à des approches de modélisation afin déterminer l’état d’oligomérisation de cette protéine en présence de détergents. Enfin, en vue de faciliter la cristallogenèse 3D, des chimères de MraY en fusion avec des protéines hydrosolubles de structure 3D résolues (mCherry et GFP) ont été construites. Des essais de cristallisation de la protéine seule et des chimères construites ont été effectués.D’autre part, nous avons élucidé le mécanisme catalytique de l’enzyme MraY et de son paralogue WecA. Au cours de ma thèse, j’ai pu montrer que cette famille de transférase membranaire présente un mécanisme catalytique commun qui procède en une seule étape par attaque directe d’un oxyanion du substrat lipidique, préalablement déprotoné par un résidu aspartate invariant, sur le phophate Beta du substrat nucléotidique. Cela conduit à la formation du produit lipidique et libération de l’UMP. / The growing emergence of multiresistance of pathogenic bacteria to currently used antibiotics is a major public health problem that requires the development of new therapeutic compounds and the identification and exploitation of novel targets. In this context, we undertook the biochemical and structural characterization of MraY enzyme, an integral membrane protein, member of the polyprenyl-phosphate N-acetylhexosamine 1-phosphate transferase superfamily. The MraY transferase catalyzes the first membrane step of bacterial cell wall peptidoglycan biosynthesis, namely the transfer of the N-acetylmuramoyl-pentapeptide moiety of the cytoplasmic precursor UDP-MurNAc-pentapeptide to the membrane transporter undecaprenyl phosphate, yielding C55-PP-MurNAc-pentapeptide (lipid I). To date, no crystal structure has been reported for this enzyme. On the one hand we have undertaken the structural characterization of this enzyme by differents biophysical approaches. Electron microscopic images after two-dimensional crystallization of the protein displayed a dimeric organisation of the MraY enzyme (size 70Å/50Å). Small X-ray scattering (SAXS) experiments have shown a radius of gyration of about 42A. The results of SAXS experiments were combined with modeling approaches to determine the oligomerization state of the protein in the presence of detergents. Finally, in order to facilitate 3D crystallisation of MraY, fusion proteins of MraY and mCherry/GFP were constructed. Crystallization trials of MraY alone and the constructed chimeras were made. On the other hand, we have elucidated the catalytic mechanism of the MraY transferase and its paralog WecA. In this study, we have shown that this family of membrane transferases has a common catalytic mechanism that proceeds by a single step displacement. During this “one-step” mechanism, the oxyanion of the poly-prenyl phosphate attacks the β phosphate of the nucleotide substrate, leading to the formation of lipid product and the liberation of UMP.

is a functionally diverse large group of proteins sharing a jelly roll β-barrel fold. An enzymatic member 3-hydroxyanthranilate-3,4-dioxygenase (HAO) and a non-enzymatic member pirin, which is a human nuclear metalloprotein of unknown function present in all human tissues, were selected for structural and functional studies in this dissertation work. HAO is an important enzyme for tryptophan catabolism and for 2-nitrobenzoic acid biodegradation. In this work, seven catalytic intermediate were captured in HAO single crystals, enabling for the first time a nearly complete structural snapshot viewing of the entire molecular oxygen activation and insertion mechanism in an iron- and O2-depedent enzyme. The rapid catalytic turnover rate was found achieved in large part by protein dynamics that facilitates O2 binding to the catalytic iron, which is bound to the enzyme by a facile 2-His-1-carboxylate ligand motif. An iron storage and chaperon mechanism was also discovered in the bacterial source of this enzyme, which led to a proposed novel biological function of a mononuclear iron-sulfur center. Although human pirin protein shares the same structural fold with HAO, its iron ion is coordinated by a 3-His-1-carboxylate ligand motif. Pirin belongs to a subset of proteins whose members are playing regulatory functions in the superfamily. In this work, pirin is shown to act as a redox sensor for the NF-κB transcription factor, a critical mediator of intracellular signaling that has been linked to cellular responses to pro-inflammatory signals which controls the expression of a vast array of genes involved in immune and stress responses.

The central dogma of molecular biology outlines the process of information transfer from a DNA sequence, to a protein chain. Beyond the step of protein synthesis, there are a variety of post-translational modifications that can take place, one of which is addition of carbohydrate chains to nascent proteins, known as glycosylation. The N-linked glycosylation pathway is responsible for the covalent attachment of multifunctional carbohydrate chains on asparagine residues of nascent proteins at Asn-X-Ser/Thr consensus sequences. These carbohydrate chains are thought to aid in cell signaling, immune recognition, and other processes. Golgi alpha-mannosidase II (GMII) is the enzyme in the N-glycosylation pathway that is responsible for cleaving two mannose linkages in the oligosaccharide GnMan5Gn2 (where Gn is N-acetylglucosamine and Man is mannose), thereby producing GnMan3Gn2 , which is the committed step in complex N-glycan synthesis. It has been speculated that GMII is an excellent therapeutic target for cancer treatment, as the unusual distribution of carbohydrates on the surface of tumour cells has been characterized in many cancers. In addition, swainsonine-—a strong, yet nonspecific inhibitor of GMII—-has been shown to block metastasis and improve the clinical outcome of patients with certain cancers, including those of the colon, breast and skin. This thesis examines Golgi alpha-mannosidase II from Drosophila melanogaster (dGMII) as a model for all GMII enzymes. First, a 1.80 Angstrom resolution crystal structure of a weak inhibitor, kifunensine, binding to dGMII provides mechanistic insights into the substrate distortion in the GMII reaction. It is hypothesized that the GMII reaction proceeds via a 1 Sinterintermedi-ate. Second, a 1.40 Angstrom resolution structure of a mutant dGMII bound to its natural substrate, GnMan5Gn, identifies key substrate binding and catalytic residues, as well as expanding the definition of the GMII active site to include two distant sugar−binding subsites. Finally, the results are taken together, with knowledge of other related enzymes to synthesize a plausible itinerary for the GMII reaction.

is a functionally diverse large group of proteins sharing a jelly roll β-barrel fold. An enzymatic member 3-hydroxyanthranilate-3,4-dioxygenase (HAO) and a non-enzymatic member pirin, which is a human nuclear metalloprotein of unknown function present in all human tissues, were selected for structural and functional studies in this dissertation work. HAO is an important enzyme for tryptophan catabolism and for 2-nitrobenzoic acid biodegradation. In this work, seven catalytic intermediate were captured in HAO single crystals, enabling for the first time a nearly complete structural snapshot viewing of the entire molecular oxygen activation and insertion mechanism in an iron- and O2-depedent enzyme. The rapid catalytic turnover rate was found achieved in large part by protein dynamics that facilitates O2 binding to the catalytic iron, which is bound to the enzyme by a facile 2-His-1-carboxylate ligand motif. An iron storage and chaperon mechanism was also discovered in the bacterial source of this enzyme, which led to a proposed novel biological function of a mononuclear iron-sulfur center. Although human pirin protein shares the same structural fold with HAO, its iron ion is coordinated by a 3-His-1-carboxylate ligand motif. Pirin belongs to a subset of proteins whose members are playing regulatory functions in the superfamily. In this work, pirin is shown to act as a redox sensor for the NF-κB transcription factor, a critical mediator of intracellular signaling that has been linked to cellular responses to pro-inflammatory signals which controls the expression of a vast array of genes involved in immune and stress responses.

The central dogma of molecular biology outlines the process of information transfer from a DNA sequence, to a protein chain. Beyond the step of protein synthesis, there are a variety of post-translational modifications that can take place, one of which is addition of carbohydrate chains to nascent proteins, known as glycosylation. The N-linked glycosylation pathway is responsible for the covalent attachment of multifunctional carbohydrate chains on asparagine residues of nascent proteins at Asn-X-Ser/Thr consensus sequences. These carbohydrate chains are thought to aid in cell signaling, immune recognition, and other processes. Golgi alpha-mannosidase II (GMII) is the enzyme in the N-glycosylation pathway that is responsible for cleaving two mannose linkages in the oligosaccharide GnMan5Gn2 (where Gn is N-acetylglucosamine and Man is mannose), thereby producing GnMan3Gn2 , which is the committed step in complex N-glycan synthesis. It has been speculated that GMII is an excellent therapeutic target for cancer treatment, as the unusual distribution of carbohydrates on the surface of tumour cells has been characterized in many cancers. In addition, swainsonine-—a strong, yet nonspecific inhibitor of GMII—-has been shown to block metastasis and improve the clinical outcome of patients with certain cancers, including those of the colon, breast and skin. This thesis examines Golgi alpha-mannosidase II from Drosophila melanogaster (dGMII) as a model for all GMII enzymes. First, a 1.80 Angstrom resolution crystal structure of a weak inhibitor, kifunensine, binding to dGMII provides mechanistic insights into the substrate distortion in the GMII reaction. It is hypothesized that the GMII reaction proceeds via a 1 Sinterintermedi-ate. Second, a 1.40 Angstrom resolution structure of a mutant dGMII bound to its natural substrate, GnMan5Gn, identifies key substrate binding and catalytic residues, as well as expanding the definition of the GMII active site to include two distant sugar−binding subsites. Finally, the results are taken together, with knowledge of other related enzymes to synthesize a plausible itinerary for the GMII reaction.