Publications

• Biochemical and structural elucidation of the L-carnitine degradation pathway of the human pathogen <i>Acinetobacter baumannii</i>.

  Piskol F., Lukat P., Kaufhold L., Heger A., Blankenfeldt W., Jahn D., Moser J.

  <i>Acinetobacter baumannii</i> is an opportunistic human pathogen which can use host-derived L-carnitine as sole carbon and energy source. Recently, an L-carnitine transporter (Aci1347) and a specific monooxygense (CntA/CntB) for the intracellular cleavage of L-carnitine have been characterized. S ... >> More

  <i>Acinetobacter baumannii</i> is an opportunistic human pathogen which can use host-derived L-carnitine as sole carbon and energy source. Recently, an L-carnitine transporter (Aci1347) and a specific monooxygense (CntA/CntB) for the intracellular cleavage of L-carnitine have been characterized. Subsequent conversion of the resulting malic semialdehyde into the central metabolite L-malate was hypothesized. Alternatively, L-carnitine degradation via D-malate with subsequent oxidation into pyruvate was proposed. Here we describe the <i>in vitro</i> and <i>in vivo</i> reconstitution of the entire pathway, starting from the as yet uncharacterized gene products of the carnitine degradation gene operon. Using recombinantly purified enzymes, enantiomer-specific formation of D-malate by the NAD(P)⁺-dependent malic semialdehyde dehydrogenase (MSA-DH) is demonstrated. The solved X-ray crystal structure of tetrameric MSA-DH reveals the key catalytic residues Cys²⁹⁰ and Glu²⁵⁶, accessible through opposing substrate and cofactor funnels. Specific substrate binding is enabled by Arg¹⁶⁶, Arg²⁸⁴ and Ser⁴⁴⁷ while dual cofactor specificity for NAD⁺ and NADP⁺ is mediated by Asn¹⁸⁴. The subsequent conversion of the unusual D-malate reaction product by an uncharacterized NAD⁺-dependent malate dehydrogenase (MDH) is shown. Tetrameric MDH is a β-decarboxylating dehydrogenase that synthesizes pyruvate. MDH experiments with alternative substrates showed a high degree of substrate specificity. Finally, the entire <i>A. baumannni</i> pathway was heterologously reconstituted, allowing <i>E. coli</i> to grow on L-carnitine as a carbon and energy source. Overall, the metabolic conversion of L-carnitine via malic semialdehyde and D-malate into pyruvate, CO₂ and trimethylamine was demonstrated. Trimethylamine is also an important gut microbiota-dependent metabolite that is associated with an increased risk of cardiovascular disease. The pathway reconstitution experiments allowed us to assess the TMA forming capacity of gut microbes which is related to human cardiovascular health. << Less

  Front Microbiol 15:1446595-1446595(2024) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Gamma-butyrobetaine is a proatherogenic intermediate in gut microbial metabolism of L-carnitine to TMAO.

  Koeth R.A., Levison B.S., Culley M.K., Buffa J.A., Wang Z., Gregory J.C., Org E., Wu Y., Li L., Smith J.D., Tang W.H., DiDonato J.A., Lusis A.J., Hazen S.L.

  L-carnitine, a nutrient in red meat, was recently reported to accelerate atherosclerosis via a metaorganismal pathway involving gut microbial trimethylamine (TMA) formation and host hepatic conversion into trimethylamine-N-oxide (TMAO). Herein, we show that following L-carnitine ingestion, γ-butyr ... >> More

  L-carnitine, a nutrient in red meat, was recently reported to accelerate atherosclerosis via a metaorganismal pathway involving gut microbial trimethylamine (TMA) formation and host hepatic conversion into trimethylamine-N-oxide (TMAO). Herein, we show that following L-carnitine ingestion, γ-butyrobetaine (γBB) is produced as an intermediary metabolite by gut microbes at a site anatomically proximal to and at a rate ∼1,000-fold higher than the formation of TMA. Moreover, we show that γBB is the major gut microbial metabolite formed from dietary L-carnitine in mice, is converted into TMA and TMAO in a gut microbiota-dependent manner (like dietary L-carnitine), and accelerates atherosclerosis. Gut microbial composition and functional metabolic studies reveal that distinct taxa are associated with the production of γBB or TMA/TMAO from dietary L-carnitine. Moreover, despite their close structural similarity, chronic dietary exposure to L-carnitine or γBB promotes development of functionally distinct microbial communities optimized for the metabolism of L-carnitine or γBB, respectively. << Less

  Cell Metab. 20:799-812(2014) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.

• Two-component carnitine monooxygenase from Escherichia coli: functional characterization, inhibition and mutagenesis of the molecular interface.

  Piskol F., Neubauer K., Eggers M., Bode L.M., Jasper J., Slusarenko A., Reijerse E., Lubitz W., Jahn D., Moser J.

  Gut microbial production of trimethylamine (TMA) from l-carnitine is directly linked to cardiovascular disease. TMA formation is facilitated by carnitine monooxygenase, which was proposed as a target for the development of new cardioprotective compounds. Therefore, the molecular understanding of t ... >> More

  Gut microbial production of trimethylamine (TMA) from l-carnitine is directly linked to cardiovascular disease. TMA formation is facilitated by carnitine monooxygenase, which was proposed as a target for the development of new cardioprotective compounds. Therefore, the molecular understanding of the two-component Rieske-type enzyme from Escherichia coli was intended. The redox cofactors of the reductase YeaX (FMN, plant-type [2Fe-2S] cluster) and of the oxygenase YeaW (Rieske-type [2Fe-2S] and mononuclear [Fe] center) were identified. Compounds meldonium and the garlic-derived molecule allicin were recently shown to suppress microbiota-dependent TMA formation. Based on two independent carnitine monooxygenase activity assays, enzyme inhibition by meldonium or allicin was demonstrated. Subsequently, the molecular interplay of the reductase YeaX and the oxygenase YeaW was addressed. Chimeric carnitine monooxygenase activity was efficiently reconstituted by combining YeaX (or YeaW) with the orthologous oxygenase CntA (or reductase CntB) from Acinetobacter baumannii. Partial conservation of the reductase/oxygenase docking interface was concluded. A structure guided mutagenesis approach was used to further investigate the interaction and electron transfer between YeaX and YeaW. Based on AlphaFold structure predictions, a total of 28 site-directed variants of YeaX and YeaW were kinetically analyzed. Functional relevance of YeaX residues Arg271, Lys313 and Asp320 was concluded. Concerning YeaW, a docking surface centered around residues Arg83, Lys104 and Lys117 was hypothesized. The presented results might contribute to the development of TMA-lowering strategies that could reduce the risk for cardiovascular disease. << Less

  Biosci Rep 42:BSR20221102-BSR20221102(2022) [PubMed] [EuropePMC]

• Carnitine metabolism in the human gut: characterization of the two-component carnitine monooxygenase CntAB from <i>Acinetobacter baumannii</i>.

  Massmig M., Reijerse E., Krausze J., Laurich C., Lubitz W., Jahn D., Moser J.

  Bacterial formation of trimethylamine (TMA) from carnitine in the gut microbiome has been linked to cardiovascular disease. During this process, the two-component carnitine monooxygenase (CntAB) catalyzes the oxygen-dependent cleavage of carnitine to TMA and malic semialdehyde. Individual redox st ... >> More

  Bacterial formation of trimethylamine (TMA) from carnitine in the gut microbiome has been linked to cardiovascular disease. During this process, the two-component carnitine monooxygenase (CntAB) catalyzes the oxygen-dependent cleavage of carnitine to TMA and malic semialdehyde. Individual redox states of the reductase CntB and the catalytic component CntA were investigated based on mutagenesis and electron paramagnetic resonance (EPR) spectroscopic approaches. Protein ligands of the flavin mononucleotide (FMN) and the plant-type [2Fe-2S] cluster of CntB and also of the Rieske-type [2Fe-2S] cluster and the mononuclear [Fe] center of CntA were identified. EPR spectroscopy of variant CntA proteins suggested a hierarchical metallocenter maturation, Rieske [2Fe-2S] followed by the mononuclear [Fe] center. NADH-dependent electron transfer <i>via</i> the redox components of CntB and within the trimeric CntA complex for the activation of molecular oxygen was investigated. EPR experiments indicated that the two electrons from NADH were allocated to the plant-type [2Fe-2S] cluster and to FMN in the form of a flavin semiquinone radical. Single-turnover experiments of this reduced CntB species indicated the translocation of the first electron onto the [Fe] center and the second electron onto the Rieske-type [2Fe-2S] cluster of CntA to finally allow for oxygen activation as a basis for carnitine cleavage. EPR spectroscopic investigation of CntA variants indicated an unusual intermolecular electron transfer between the subunits of the CntA trimer <i>via</i> the "bridging" residue Glu-205. On the basis of these data, a redox catalytic cycle for carnitine monooxygenase was proposed. << Less

  J Biol Chem 295:13065-13078(2020) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Carnitine metabolism to trimethylamine by an unusual Rieske-type oxygenase from human microbiota.

  Zhu Y., Jameson E., Crosatti M., Schaefer H., Rajakumar K., Bugg T.D., Chen Y.

  Dietary intake of L-carnitine can promote cardiovascular diseases in humans through microbial production of trimethylamine (TMA) and its subsequent oxidation to trimethylamine N-oxide by hepatic flavin-containing monooxygenases. Although our microbiota are responsible for TMA formation from carnit ... >> More

  Dietary intake of L-carnitine can promote cardiovascular diseases in humans through microbial production of trimethylamine (TMA) and its subsequent oxidation to trimethylamine N-oxide by hepatic flavin-containing monooxygenases. Although our microbiota are responsible for TMA formation from carnitine, the underpinning molecular and biochemical mechanisms remain unclear. In this study, using bioinformatics approaches, we first identified a two-component Rieske-type oxygenase/reductase (CntAB) and associated gene cluster proposed to be involved in carnitine metabolism in representative genomes of the human microbiota. CntA belongs to a group of previously uncharacterized Rieske-type proteins and has an unusual "bridging" glutamate but not the aspartate residue, which is believed to facilitate intersubunit electron transfer between the Rieske center and the catalytic mononuclear iron center. Using Acinetobacter baumannii as the model, we then demonstrate that cntAB is essential in carnitine degradation to TMA. Heterologous overexpression of cntAB enables Escherichia coli to produce TMA, confirming that these genes are sufficient in TMA formation. Site-directed mutagenesis experiments have confirmed that this unusual "bridging glutamate" residue in CntA is essential in catalysis and neither mutant (E205D, E205A) is able to produce TMA. Taken together, the data in our study reveal the molecular and biochemical mechanisms underpinning carnitine metabolism to TMA in human microbiota and assign the role of this novel group of Rieske-type proteins in microbial carnitine metabolism. << Less

  Proc. Natl. Acad. Sci. U.S.A. 111:4268-4273(2014) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• CntA oxygenase substrate profile comparison and oxygen dependency of TMA production in Providencia rettgeri.

  Kalnins G., Sevostjanovs E., Hartmane D., Grinberga S., Tars K.

  CntA oxygenase is a Rieske 2S-2Fe cluster-containing protein that has been previously described as able to produce trimethylamine (TMA) from carnitine, gamma-butyrobetaine, glycine betaine, and in one case, choline. TMA found in humans is exclusively of bacterial origin, and its metabolite, trimet ... >> More

  CntA oxygenase is a Rieske 2S-2Fe cluster-containing protein that has been previously described as able to produce trimethylamine (TMA) from carnitine, gamma-butyrobetaine, glycine betaine, and in one case, choline. TMA found in humans is exclusively of bacterial origin, and its metabolite, trimethylamine oxide (TMAO), has been associated with atherosclerosis and heart and renal failure. We isolated four different Rieske oxygenases and determined that there are no significant differences in their substrate panels. All three had high activity toward carnitine/gamma-butyrobetaine, medium activity toward glycine betaine, and very low activity toward choline. We tested the influence of low oxygen concentrations on TMA production in CntA-containing Providencia rettgeri cell cultures and discovered that this process, although dependent on the amount of oxygen, is still feasible in environments with 1 and 0.2% oxygen, which is comparable to oxygen levels in some parts of the digestive system. << Less

  J Basic Microbiol 58:52-59(2018) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Structural basis of carnitine monooxygenase CntA substrate specificity, inhibition, and intersubunit electron transfer.

  Quareshy M., Shanmugam M., Townsend E., Jameson E., Bugg T.D.H., Cameron A.D., Chen Y.

  Microbial metabolism of carnitine to trimethylamine (TMA) in the gut can accelerate atherosclerosis and heart disease, and these TMA-producing enzymes are therefore important drug targets. Here, we report the first structures of the carnitine oxygenase CntA, an enzyme of the Rieske oxygenase famil ... >> More

  Microbial metabolism of carnitine to trimethylamine (TMA) in the gut can accelerate atherosclerosis and heart disease, and these TMA-producing enzymes are therefore important drug targets. Here, we report the first structures of the carnitine oxygenase CntA, an enzyme of the Rieske oxygenase family. CntA exists in a head-to-tail α₃ trimeric structure. The two functional domains (the Rieske and the catalytic mononuclear iron domains) are located >40 Å apart in the same monomer but adjacent in two neighboring monomers. Structural determination of CntA and subsequent electron paramagnetic resonance measurements uncover the molecular basis of the so-called bridging glutamate (E205) residue in intersubunit electron transfer. The structures of the substrate-bound CntA help to define the substrate pocket. Importantly, a tyrosine residue (Y203) is essential for ligand recognition through a π-cation interaction with the quaternary ammonium group. This interaction between an aromatic residue and quaternary amine substrates allows us to delineate a subgroup of Rieske oxygenases (group V) from the prototype ring-hydroxylating Rieske oxygenases involved in bioremediation of aromatic pollutants in the environment. Furthermore, we report the discovery of the first known CntA inhibitors and solve the structure of CntA in complex with the inhibitor, demonstrating the pivotal role of Y203 through a π-π stacking interaction with the inhibitor. Our study provides the structural and molecular basis for future discovery of drugs targeting this TMA-producing enzyme in human gut. << Less

  J Biol Chem 296:100038-100038(2021) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• L-carnitine via enzyme-catalyzed oxidative kinetic resolution.

  Ditullio D., Anderson D., Chen C.S., Sih C.J.

  L-Carnitine of high optical purity was prepared via kinetic resolution using a mutant strain of Acinetobacter calcoaceticus ATCC 39647. This organism preferentially metabolized the D-enantiomer of the racemate to furnish L-carnitine. Recovery of L-carnitine was 93%, providing a total weight yield ... >> More

  L-Carnitine of high optical purity was prepared via kinetic resolution using a mutant strain of Acinetobacter calcoaceticus ATCC 39647. This organism preferentially metabolized the D-enantiomer of the racemate to furnish L-carnitine. Recovery of L-carnitine was 93%, providing a total weight yield of 46.5% in 92% enantiomeric excess. The mode of degradation of carnitine was shown to proceed via a monooxygenase-catalyzed oxidative cleavage resulting in the formation of trimethylamine and malic acid. The data suggest that the stereoselective metabolism of DL-carnitine is probably the result of differential permeability of the cell membrane towards the optical antipodes. << Less

  Bioorg. Med. Chem. 2:415-420(1994) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.