Stereochemistry of acetic acid formation from 5-methyltetrahydrofolate by Clostridium thermoaceticum

Carbon dioxide and carbon monoxide are important components of the carbon cycle. Major research efforts are underway to develop better technologies to utilize the abundant greenhouse gas, CO2, for harnessing ‘green’ energy and producing biofuels. One strategy is to convert CO2 into CO, which has been valued for many years as a synthetic feedstock for major industrial processes. Living organisms are masters of CO2 and CO chemistry and, here, we review the elegant ways that metalloenzymes catalyze reactions involving these simple compounds. After describing the chemical and physical properties of CO and CO2, we shift focus to the enzymes and the metal clusters in their active sites that catalyze transformations of these two molecules. We cover how the metal centers on CO dehydrogenase catalyze the interconversion of CO and CO2 and how pyruvate oxidoreductase, which contains thiamin pyrophosphate and multiple Fe4S4 clusters, catalyzes the addition and elimination of CO2 during intermediary metabolism. We also describe how the nickel center at the active site of acetyl-CoA synthase utilizes CO to generate the central metabolite, acetyl-CoA, as part of the Wood-Ljungdahl pathway, and how CO is channelled from the CO dehydrogenase to the acetyl-CoA synthase active site. We cover how the corrinoid iron–sulfur protein interacts with acetyl-CoA synthase. This protein uses vitamin B12 and a Fe4S4 cluster to catalyze a key methyltransferase reaction involving an organometallic methyl-Co3+ intermediate. Studies of CO and CO2 enzymology are of practical significance, and offer fundamental insights into important biochemical reactions involving metallocenters that act as nucleophiles to form organometallic intermediates and catalyze C–C and C–S bond formations.

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“…229 (iv) The methyl group of chiral CH 3 –H 4 folate is converted to acetyl-CoA with retention of configuration. 237 …”

Section: (V) Enzymatic Reactions Involving Co and Co2mentioning

confidence: 99%

Metal centers in the anaerobic microbial metabolism of CO and CO2

et al. 2011

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“…This reaction occurs at a rate similar to that of acetyl-CoA synthesis and involves cleavage of the C-C and C-S bonds of acetyl-CoA to form a quaternary complex in which 14 CO, CH 3 , and CoA independently bind to ACS; then bound 14 CO undergoes isotopic exchange with CO in solution (25)(26)(27). This reaction occurs with retention of stereochemical configuration at the methyl moiety of acetyl-CoA (9). CODH⅐ACS also catalyzes a CoA/acetyl-CoA exchange between CoA and acetyl-CoA (Equation 5).…”

mentioning

confidence: 97%

Pulse-Chase Studies of the Synthesis of Acetyl-CoA by Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase

Seravalli

Ragsdale

2008

Journal of Biological Chemistry

103

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Carbon monoxide dehydrogenase/acetyl-CoA synthase catalyzes acetyl-CoA synthesis from CO, CoA, and a methylated corrinoid iron-sulfur protein, which acts as a methyl donor. This reaction is the last step in the Wood-Ljungdahl pathway of anaerobic carbon fixation. The binding sequence for the three substrates has been debated for over a decade. Different binding orders imply different mechanisms (i.e. paramagnetic versus diamagnetic mechanisms). Ambiguity arises because CO and CoA can each undergo isotopic exchange with acetyl-CoA, suggesting that either of these two substrates could be the last to bind to the acetyl-CoA synthase active site. Furthermore, carbonylation, CoA binding, and methyl transfer can all occur in the absence of the other two substrates. Here, we report pulsechase studies, which unambiguously establish the order in which the three substrates bind. Although a CoA pulse is substantially diluted by excess CoA in the chase, isotope recovery of a pulse of labeled CO or methyl group is unaffected by the presence of excess unlabeled CO or methyl group in the chase. These results demonstrate that CoA is the last substrate to bind and that CO and the methyl group bind randomly as the first substrate in acetyl-CoA synthesis. Up to 100% of the methyl groups and CoA and up to 60 -70% of the CO employed in the pulse phase can be trapped in the product acetyl-CoA.There are three types of CO dehydrogenase (CODH) 2 (1, 2). These include a copper molybdopterin iron-sulfur protein that is present in aerobic bacteria and an NiFeS enzyme that is present in anaerobic microbes. These enzymes allow microbes to utilize CO at the low concentrations present in the atmosphere as a carbon and electron source. A third type of CODH is highly homologous to the monofunctional NiFeS enzyme and is found tightly associated with another NiFeS enzyme called acetyl-CoA synthase (ACS), forming the CODH⅐ACS complex.CODH⅐ACS is a macromolecular machine that catalyzes the last step of the Wood-Ljungdahl pathway of anaerobic carbon dioxide fixation (Reaction 1). The 300-kDa ␣ 2 ␤ 2 heterotetramer is composed of two types of subunits. The 72-kDa ␤-subunit is CODH, which catalyzes the reversible oxidation of CO to CO 2 (Reaction 2) at the C-cluster, a novel [NiFe 4 S 4 -5 ] cluster (3, 4), whereas the 82-kDa ␣-subunit is ACS, which catalyzes the condensation of three substrates, CoA, CO, and a methyl group from the methylated corrinoid iron-sulfur protein (CH 3 -CFeSP), to produce acetyl-CoA. Methylation of the CFeSP is accomplished by a methyltransferase (MeTr), which catalyzes the transfer of a methyl group from CH 3 -H 4 folate to the Co(I) state of the CFeSP, according to Reaction 3 (5). Although MeTr contains no metals or other cofactors, the CFeSP contains a corrinoid cofactor and a [Fe 4 S 4 ] cluster, which is involved in the reactivation of the cobalt center back to the 1ϩ state whenever it has undergone oxidation (approximately once in every 1000 catalytic cycles) (6, 7). The resulting CH 3 -CFeSP becomes the methyl donor to ...

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“…We were unable to detect any reduction or cleavage of the methyl-Co(III) state of the CFeSP after several hours of incubation in the presence of CO and CODH/ACS (9). Mechanism I is also supported by studies of acetyl-CoA synthesis using chiral CH 3 -H 4 folate, which is converted to acetyl-CoA with retention of configuration (44). The most straightforward interpretation of these studies is that transfer of the methyl group to CODH occurs with inversion of configuration, as expected for an S N 2 type displacement.…”

Section: [4fe-4s] Cluster Requirement For Bmentioning

confidence: 78%

The Role of an Iron-Sulfur Cluster in an Enzymatic Methylation Reaction

Menon¹,

Ragsdale

1999

Journal of Biological Chemistry

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This paper focuses on how a methyl group is transferred from a methyl-cobalt(III) species on one protein (the corrinoid iron-sulfur protein (CFeSP)) to a nickel iron-sulfur cluster on another protein (carbon monoxide dehydrogenase/acetyl-CoA synthase). This is an essential step in the Wood-Ljungdahl pathway of anaerobic CO and CO 2 fixation. The results described here strongly indicate that transfer of methyl group to carbon monoxide dehydrogenase/acetyl-CoA synthase occurs by an S N 2 pathway. They also provide convincing evidence that oxidative inactivation of Co(I) competes with methylation. Under the conditions of our anaerobic assay, Co(I) escapes from the catalytic cycle one in every 100 turnover cycles. Reductive activation of the CFeSP is required to regenerate Co(I) and recruit the protein back into the catalytic cycle. Our results strongly indicate that the [4Fe-4S] cluster of the CFeSP is required for reductive activation. They support the hypothesis that the [4Fe-4S] cluster of the CFeSP does not participate directly in the methyl transfer step but provides a conduit for electron flow from physiological reductants to the cobalt center.

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Stereochemistry of acetic acid formation from 5-methyltetrahydrofolate by Clostridium thermoaceticum

Cited by 56 publications

References 1 publication

Metal centers in the anaerobic microbial metabolism of CO and CO2

Metal centers in the anaerobic microbial metabolism of CO and CO2

Pulse-Chase Studies of the Synthesis of Acetyl-CoA by Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase

The Role of an Iron-Sulfur Cluster in an Enzymatic Methylation Reaction

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