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Mechanism of inhibition of aliphatic epoxide carboxylation by the coenzyme M analog 2-bromoethanesulfonate.

ABSTRACT: The bacterial metabolism of epoxypropane formed from propylene oxidation uses the atypical cofactor coenzyme M (CoM, 2-mercaptoethanesulfonate) as the nucleophile for epoxide ring opening and as a carrier of intermediates that undergo dehydrogenation, reductive cleavage, and carboxylation to form acetoacetate in a three-step metabolic pathway. 2-Ketopropyl-CoM carboxylase/oxidoreductase (2-KPCC), the terminal enzyme of this pathway, is the only known member of the disulfide oxidoreductase family of enzymes that is a carboxylase. In the present work, the CoM analog 2-bromoethanesulfonate (BES) is shown to be a reversible inhibitor of 2-KPCC and hydroxypropyl-CoM dehydrogenase but not of epoxyalkane:CoM transferase. Further investigations revealed that BES is a time-dependent inactivator of dithiothreitol-reduced 2-KPCC, where the redox active cysteines are in the free thiol forms. BES did not inactivate air-oxidized 2-KPCC, where the redox active cysteine pair is in the disulfide form. The inactivation of 2-KPCC exhibited saturation kinetics, and CoM slowed the rate of inactivation. Mass spectral analysis demonstrated that BES inactivation of reduced 2-KPCC occurs with covalent modification of the interchange thiol (Cys(82)) by a group with a molecular mass identical to that of ethylsulfonate. The flavin thiol Cys(87) was not alkylated by BES under reducing conditions, and no amino acid residues were modified by BES in the oxidized enzyme. The UV-visible spectrum of BES-modifed 2-KPCC showed the characteristic charge transfer absorbance expected with alkylation at Cys(82). These results identify BES as a reactive CoM analog that specifically alkylates the interchange thiol that facilitates thioether bond cleavage and enolacetone formation during catalysis.

SUBMITTER: Boyd JM

PROVIDER: S-EPMC2919086 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Mechanism of inhibition of aliphatic epoxide carboxylation by the coenzyme M analog 2-bromoethanesulfonate.

Boyd Jeffrey M JM Clark Daniel D DD Kofoed Melissa A MA Ensign Scott A SA

The Journal of biological chemistry 20100615 33

The bacterial metabolism of epoxypropane formed from propylene oxidation uses the atypical cofactor coenzyme M (CoM, 2-mercaptoethanesulfonate) as the nucleophile for epoxide ring opening and as a carrier of intermediates that undergo dehydrogenation, reductive cleavage, and carboxylation to form acetoacetate in a three-step metabolic pathway. 2-Ketopropyl-CoM carboxylase/oxidoreductase (2-KPCC), the terminal enzyme of this pathway, is the only known member of the disulfide oxidoreductase family ...[more]

PMID: 20551308

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Project description:(R)- and (S)-2-hydroxypropyl-CoM (R-HPC and S-HPC) are produced as intermediates in bacterial propylene metabolism from the nucleophilic addition of coenzyme M to (R)- and (S)-epoxypropane, respectively. Two highly enantioselective dehydrogenases (R-HPCDH and S-HPCDH) belonging to the short-chain dehydrogenase/reductase family catalyze the conversion of R-HPC and S-HPC to 2-ketopropyl-CoM (2-KPC), which undergoes reductive cleavage and carboxylation to produce acetoacetate. In the present study, one of three copies of S-HPCDH enzymes present on a linear megaplasmid in Xanthobacter autotrophicus strain Py2 has been cloned and overexpressed, allowing the first detailed side by side characterization of the R-HPCDH and S-HPCDH enzymes. The catalytic triad of S-HPCDH was found to consist of Y156, K160, and S143. R211 and K214 were identified as the amino acid residues coordinating the sulfonate of CoM in S-HPC. R211A and K214A mutants were severely impaired in the oxidation of S-HPC or reduction of 2-KPC but were largely unaffected in the oxidation and reduction of aliphatic alcohols and ketones. Kinetic analyses using R- and S-HPC as substrates revealed that enantioselectivity in R-HPCDH (value, 944) was dictated largely by differences in k(cat) while enantioselectivity for S-HPCDH (value, 1315) was dictated largely by changes in K(m). S-HPCDH had an inherent high enantioselectivity for producing (S)-2-butanol from 2-butanone that was unaffected by modulators that interact with the sulfonate binding site. The tertiary alcohol 2-methyl-2-hydroxypropyl-CoM (M-HPC) was a competitive inhibitor of R-HPCDH-catalyzed R-HPC oxidation, with a K(is) similar to the K(m) for R-HPC, but was not an inhibitor of S-HPCDH. The primary alcohol 2-hydroxyethyl-CoM was a substrate for both R-HPCDH and S-HPCDH with identical K(m) values. The pH dependence of kinetic parameters suggests that the hydroxyl group is a larger contributor to S-HPC binding to S-HPCDH than for R-HPC binding to R-HPCDH. It is proposed that active site constraints within the S-HPCDH prevent proper binding of R-HPC and M-HPC due to steric clashes with the improperly aligned methyl group on the C2 carbon, resulting in a different mechanism for controlling substrate specificity and enantioselectivity than present in the R-HPCDH.

Project description:Degradation of long-chain fatty acids (LCFAs) in methanogenic environments is a syntrophic process involving the activity of LCFA-degrading bacteria and hydrogen-utilizing methanogens. If methanogens are inhibited, other hydrogen scavengers are needed to achieve complete LCFA degradation. In this work, we developed two different oleate (C18:1 LCFA)-degrading anaerobic enrichment cultures, one methanogenic (ME) and another in which methanogenesis was inhibited (IE). Inhibition of methanogens was attained by adding a solution of 2-bromoethanesulfonate (BrES), which turned out to consist of a mixture of BrES and isethionate. Approximately 5 times faster oleate degradation was accomplished by the IE culture compared with the ME culture. A bacterium closely related to Syntrophomonas zehnderi (99% 16S rRNA gene identity) was the main oleate degrader in both enrichments, in syntrophic relationship with hydrogenotrophic methanogens from the genera Methanobacterium and Methanoculleus (in ME culture) or with a bacterium closely related to Desulfovibrio aminophilus (in IE culture). A Desulfovibrio species was isolated, and its ability to utilize hydrogen was confirmed. This bacterium converted isethionate to acetate and sulfide, with or without hydrogen as electron donor. This bacterium also utilized BrES but only after 3 months of incubation. Our study shows that syntrophic oleate degradation can be coupled to desulfonation.IMPORTANCE In anaerobic treatment of complex wastewater containing fat, oils, and grease, high long-chain fatty acid (LCFA) concentrations may inhibit microbial communities, particularly those of methanogens. Here, we investigated if anaerobic degradation of LCFAs can proceed when methanogens are inhibited and in the absence of typical external electron acceptors, such as nitrate, iron, or sulfate. Inhibition studies were performed with the methanogenic inhibitor 2-bromoethanesulfonate (BrES). We noticed that, after autoclaving, BrES underwent partial hydrolysis and turned out to be a mixture of two sulfonates (BrES and isethionate). We found out that LCFA conversion proceeded faster in the assays where methanogenesis was inhibited, and that it was dependent on the utilization of isethionate. In this study, we report LCFA degradation coupled to desulfonation. Our results also showed that BrES can be utilized by anaerobic bacteria.

Project description:BackgroundNeuroinflammation is widely recognized as a significant hallmark of Alzheimer's disease (AD). To combat neuroinflammation, the inhibition of the soluble epoxide hydrolase (sEH) enzyme has been demonstrated crucial. Importantly, sEH inhibition could be related to other neuroprotective pathways described in AD.AimsThe aim of the study was to unveil new molecular pathways driving neuroprotection through sEH, we used an optimized, potent, and selective sEH inhibitor (sEHi, UB-SCG-51).Materials and methodsUB-SCG-51 was tested in neuroblastoma cell line, SH-SY5Y, in primary mouse and human astrocytes cultures challenged with proinflammatory insults and in microglia cultures treated with amyloid oligomers, as well as in mice AD model (5XFAD).ResultsUB-SCG-51 (10 and 30 μM) prevented neurotoxic reactive-astrocyte conversion in primary mouse astrocytes challenged with TNF-α, IL-1α, and C1q (T/I/C) combination for 24 h. Moreover, in microglial cultures, sEHi reduced inflammation and glial activity. In addition, UB-SCG-51 rescued 5XFAD cognitive impairment, reducing the number of Amyloid-β plaques and Tau hyperphosphorylation accompanied by a reduction in neuroinflammation and apoptotic markers. Notably, a transcriptional profile analysis revealed a new pathway modulated by sEHi treatment. Specifically, the eIF2α/CHOP pathway, which promoted the endoplasmic reticulum response, was increased in the 5XFAD-treated group. These findings were confirmed in human primary astrocytes by combining sEHi and eIF2α inhibitor (eIF2αi) treatment. Besides, combining both treatments resulted in increased in C3 gene expression after T/I/C compared with the group treated with sEHi alone in cultures.DiscussionTherefore, sEHi rescued cognitive impairment and neurodegeneration in AD mice model, based on the reduction of inflammation and eIF2α/CHOP signaling pathway.ConclusionsIn whole, our results support the concept that targeting neuroinflammation through sEH inhibition is a promising therapeutic strategy to fight against Alzheimer's disease with additive and/or synergistic activities targeting neuroinflammation and cell stress.

Dataset Information

Mechanism of inhibition of aliphatic epoxide carboxylation by the coenzyme M analog 2-bromoethanesulfonate.

Publications

Mechanism of inhibition of aliphatic epoxide carboxylation by the coenzyme M analog 2-bromoethanesulfonate.

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