Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.2.1.1 (ACS)
 78,556 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The structure of carbon monoxide dehydrogenase/acetyl-coenzyme A synthase (CODH/ACS), a central enzyme in the anaerobic metabolism of acetyl-coenzyme A (acetyl-CoA), has been solved to a resolution of 2.2A. The active-site metal cluster responsible for catalyzing acetyl C-C bond synthesis and cleavage, designated the A center, was identified as an Fe(4)S(4) iron sulfur cluster with one of its cysteine thiolates acting as a bridge to an adjacent binuclear metal site. Nickel was found at one position in the binuclear site and the other metal was indicated to be copper - a surprising result, implying a previously unrecognized role for copper. Details of the A center provided new insight into the unusual organometallic mechanism of acetyl C-C bond formation and cleavage, with substantial conformational changes indicated for binding of the large methylcorrinoid protein substrate, and a unique intramolecular channel acting to contain carbon monoxide within the protein and transfer it to the site needed for acetyl-CoA synthesis.
 ...
PMID:Acetate C-C bond formation and decomposition in the anaerobic world: the structure of a central enzyme and its key active-site metal cluster. 1276 30

Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) is a bifunctional enzyme that catalyzes the reversible reduction of carbon dioxide into carbon monoxide and the coupled synthesis of acetyl-CoA from the carbon monoxide produced. Exposure of CODH/ACS from Moorella thermoacetica to carbon monoxide gives rise to several infrared bands in the 2100-1900 cm(-1) spectral region that are attributed to the formation of metal-coordinated carbon monoxide species. Infrared bands attributable to M-CO are not detected in the as-isolated enzyme, suggesting that the enzyme does not contain intrinsic metal-coordinated CO ligands. A band detected at 1996 cm(-1) in the CO-flushed enzyme is assigned as arising from CO binding to a metal center in cluster A of the ACS subunit. The frequency of this band is most consistent with it arising from a terminally coordinated Ni(I) carbonyl. Multiple infrared bands at 2078, 2044, 1970, 1959, and 1901 cm(-1) are attributed to CO binding at cluster C of the CODH subunit. All infrared bands attributed to metal carbonyls decay in a time-dependent fashion as CO(2) appears in the solution. These observations are consistent with the enzyme-catalyzed oxidation of carbon monoxide until it is completely depleted from solution during the course of the experiments.
 ...
PMID:Infrared studies of carbon monoxide binding to carbon monoxide dehydrogenase/acetyl-CoA synthase from Moorella thermoacetica. 1467 56

Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) utilizes a unique Ni-M bimetallic site in the biosynthesis of acetyl-CoA, where a square-planar Ni ion is coordinated to two thiolates and two deprotonated amides in a Cys-Gly-Cys motif. The identity of M is currently a matter of debate, although both Cu and Ni have been proposed. In an effort to model ACS's unusual active site and to provide insight into the mechanism of acetyl-CoA formation and the role of each of the metals ions, we have prepared and structurally characterized a number of Ni(II)-peptide mimic complexes. The mononuclear complexes Ni(II) N, N'-bis(2-mercaptoethyl)oxamide (1), Ni(II) N, N'-ethylenebis(2-mercaptoacetamide) (2), and Ni(II) N, N'-ethylenebis(2-mercaptopropionamide) (3) model the Ni(Cys-Gly-Cys) site and can be used as synthons for additional multinuclear complexes. Reaction of 2 with MeI resulted in the alkylation of the sulfur atoms and the formation of Ni(II) N, N'-ethylenebis(2-methylmercaptoacetamide) (4), demonstrating the nucleophilicity of the terminal alkyl thiolates. Addition of Ni(OAc)(2).4H(2)O to3 resulted in the formation of a trinuclear species (5), while 2 crystallizes as an unusual paddlewheel complex (6) in the presence of nickel acetate. The difference in reactivity between the similar complexes 2 and 3 highlights the importance of ligand design when synthesizing models of ACS. Significantly,5 maintains the key features observed in the active site of ACS, namely a square-planar Ni coordinated to two deprotonated amides and two thiolates, where the thiolates bridge to a second metal, suggesting that 5 is a reasonable structural model for this unique enzyme.
 ...
PMID:Modeling carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS): a trinuclear nickel complex employing deprotonated amides and bridging thiolates. 1473 32

Acetyl-coenzyme A (CoA) synthase/carbon monoxide dehydrogenase (ACS/CODH) is a bifunctional enzyme that generates CO from carbon dioxide in the C-cluster of the beta subunit and synthesizes acetyl-CoA from carbon monoxide (CO), CoA, and CH3+ at the active site of the A-cluster in the alpha subunit. On the basis of density functional calculations, we predict that methylation of Nip occurs first, and CO then adds to the NipII-CH3 species to form the intermediate, NipII(CO)(CH3), in which Nip deligates one of its SNid bonds. The CO-insertion/CH3-migration occurs on one metal, the proximal Ni, forming the trigonal planar NipII-acetyl intermediate. The thiolate can bind to NipII and reductively eliminate the thioester. Our calculations disfavor the unprecedented bimetallic CO-insertion/CH3-migration. Ni in the proximal site produces a better catalyst than does Cu.
 ...
PMID:Structures and energetics of models for the active site of acetyl-coenzyme a synthase: role of distal and proximal metals in catalysis. 1502 53

For the last two decades, the bifunctional enzyme acetyl-coenzyme A synthase/carbon monoxide dehydrogenase (ACS/CODH) from Moorella thermoacetica has been the subject of considerable research aimed at elucidating the geometric and electronic properties of the A-cluster, which serves as the active site for ACS catalysis. While the recent success in obtaining high-resolution X-ray structures of this enzyme solved many of the mysteries regarding the number, identities, and coordination environments of the metal centers of the A-cluster, fundamental questions concerning the catalytic mechanism of this highly elaborate polynuclear active site have yet to be answered. This Commentary summarizes relevant information obtained from spectroscopic and computational studies on the oxidized, reduced, and CO-bound forms of the A-cluster and highlights some of the key issues regarding the electronic properties and reactivity of this cluster that need to be addressed in future studies.
 ...
PMID:Spectroscopic and computational insights into the geometric and electronic properties of the A-cluster of acetyl-coenzyme A synthase. 1522 80

The bifunctional enzyme carbon monoxide dehydrogenase/acetyl-coenzyme A (CoA) synthase (CODH/ACS) is a key enzyme in the Wood-Ljungdahl pathway of carbon fixation. Carbon monoxide is combined with a methyl group and ultimately converted to acetyl-CoA at a unique Ni-containing bimetallic site in the A-cluster of this enzyme. Despite years of extensive biochemical and spectroscopic studies and the recent report of three separate crystal structures, the mechanism by which acetyl-CoA is synthesized is still unknown. Over the past two years there have been a number of significant developments regarding ACS. This Account critically examines these recent developments and especially focuses on those areas that are still a matter of debate.
 ...
PMID:Unraveling the structure and mechanism of acetyl-coenzyme A synthase. 1549 Nov 24

The effect of [CO] on acetyl-CoA synthesis activity of the isolated alpha subunit of acetyl-coenzyme A synthase/carbon monoxide dehydrogenase from Moorella thermoacetica was determined. In contrast to the complete alpha(2)beta(2) enzyme where multiple CO molecules exhibit strong cooperative inhibition, alpha was weakly inhibited, apparently by a single CO with K(I) = 1.5 +/- 0.5 mM; other parameters include k(cat) = 11 +/- 1 min(-)(1) and K(M) = 30 +/- 10 microM. The alpha subunit lacked the previously described "majority" activity of the complete enzyme but possessed its "residual" activity. The site affording cooperative inhibition may be absent or inoperative in isolated alpha subunits. Ni-activated alpha rapidly and reversibly accepted a methyl group from CH(3)-Co(3+)FeSP affording the equilibrium constant K(MT) = 10 +/- 4, demonstrating the superior nucleophilicity of alpha(red) relative to Co(1+)FeSP. CO inhibited this reaction weakly (K(I) = 540 +/- 190 microM). NiFeC EPR intensity of alpha developed in accordance with an apparent K(d) = 30 microM, suggesting that the state exhibiting this signal is not responsible for inhibiting catalysis or methyl group transfer and that it may be a catalytic intermediate. At higher [CO], signal intensity declined slightly. Attenuation of catalysis, methyl group transfer, and the NiFeC signal might reflect the same weak CO binding process. Three mutant alpha(2)beta(2) proteins designed to block the tunnel between the A- and C-clusters exhibited little/no activity with CO(2) as a substrate and no evidence of cooperative CO inhibition. This suggests that the tunnel was blocked by these mutations and that cooperative CO inhibition is related to tunnel operation. Numerous CO molecules might bind cooperatively to some region associated with the tunnel and institute a conformational change that abolishes the majority activity. Alternatively, crowding of CO in the tunnel may control flow through the tunnel and deliver CO to the A-cluster at the appropriate step of catalysis. Residual activity may involve CO from the solvent binding directly to the A-cluster.
 ...
PMID:The tunnel of acetyl-coenzyme a synthase/carbon monoxide dehydrogenase regulates delivery of CO to the active site. 1583 81

Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) is a bifunctional enzyme which enables archaea and bacteria to grow autotrophically on CO and hydrogen/carbon dioxide using the Wood-Ljundahl pathway. CO produced from reduction of carbon dioxide by CODH is transferred to the active site of ACS through an intramolecular tunnel, where it combines with Coenzyme A and a methyl cation to produce acetyl-CoA. The active site of ACS contains a single [4Fe-4S] cluster bridged by a cysteine sulfur atom to a binuclear center. The binuclear center is composed of two Ni atoms bridged by two separate cysteine sulfurs. The Ni site attached to the [4Fe-4S] is referred to as proximal Ni, while the other Ni atom, which assumes a square-planar geometry, is referred to as the distal site. We report the characterization of the carbonylated form of highly active (0.67 spins/mol) heterologously expressed monomeric ACS from C. hydrogenoformans in E. coli by rapid-freeze quench EPR (RFQ-EPR) and stopped-flow infrared (SF-IR) spectroscopies. The reaction of ACS with CO produces a single metal-carbonyl species whose formation rate, measured by SF-IR, correlates with the rate of formation, measured by RFQ-EPR, of the paramagnetic state of the enzyme (NiFeC species). These results indicate that the NiFeC species is the predominant form observed in solution when ACS reacts with CO. The NiFeC species contains the proximal Ni in the +1 redox state and the [4Fe-4S] cluster in the 2+ state, thus there is no evidence for either a Ni(0) or a Ni(II) state in the active carbonylated form of the enzyme.
 ...
PMID:EPR and infrared spectroscopic evidence that a kinetically competent paramagnetic intermediate is formed when acetyl-coenzyme A synthase reacts with CO. 1619 Jul 5

Methanosphaera stadtmanae has the most restricted energy metabolism of all methanogenic archaea. This human intestinal inhabitant can generate methane only by reduction of methanol with H2 and is dependent on acetate as a carbon source. We report here the genome sequence of M. stadtmanae, which was found to be composed of 1,767,403 bp with an average G+C content of 28% and to harbor only 1,534 protein-encoding sequences (CDS). The genome lacks 37 CDS present in the genomes of all other methanogens. Among these are the CDS for synthesis of molybdopterin and for synthesis of the carbon monoxide dehydrogenase/acetyl-coenzyme A synthase complex, which explains why M. stadtmanae cannot reduce CO2 to methane or oxidize methanol to CO2 and why this archaeon is dependent on acetate for biosynthesis of cell components. Four sets of mtaABC genes coding for methanol:coenzyme M methyltransferases were found in the genome of M. stadtmanae. These genes exhibit homology to mta genes previously identified in Methanosarcina species. The M. stadtmanae genome also contains at least 323 CDS not present in the genomes of all other archaea. Seventy-three of these CDS exhibit high levels of homology to CDS in genomes of bacteria and eukaryotes. These 73 CDS include 12 CDS which are unusually long (>2,400 bp) with conspicuous repetitive sequence elements, 13 CDS which exhibit sequence similarity on the protein level to CDS encoding enzymes involved in the biosynthesis of cell surface antigens in bacteria, and 5 CDS which exhibit sequence similarity to the subunits of bacterial type I and III restriction-modification systems.
 ...
PMID:The genome sequence of Methanosphaera stadtmanae reveals why this human intestinal archaeon is restricted to methanol and H2 for methane formation and ATP synthesis. 1638 54

Methanococcus maripaludis is a mesophilic archaeon that reduces CO2 to methane with H2 or formate as an energy source. It contains two membrane-bound energy-conserving hydrogenases, Eha and Ehb. To determine the role of Ehb, a deletion in the ehb operon was constructed to yield the mutant, strain S40. Growth of S40 was severely impaired in minimal medium. Both acetate and yeast extract were necessary to restore growth to nearly wild-type levels, suggesting that Ehb was involved in multiple steps in carbon assimilation. However, no differences in the total hydrogenase specific activities were found between the wild type and mutant in either cell extracts or membrane-purified fractions. Methanogenesis by resting cells with pyruvate as the electron donor was also reduced by 30% in S40, suggesting a defect in pyruvate oxidation. CO dehydrogenase/acetyl coenzyme A (CoA) synthase and pyruvate oxidoreductase had higher specific activities in the mutant, and genes encoding these enzymes, as well as AMP-forming acetyl-CoA synthetase, were expressed at increased levels. These observations support a role for Ehb in anabolic CO2 assimilation in methanococci.
 ...
PMID:Disruption of the operon encoding Ehb hydrogenase limits anabolic CO2 assimilation in the archaeon Methanococcus maripaludis. 1645 19


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>