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Shimizu M, Makiguchi M, Hishinuma E, Saito S, Hiratsuka M, Yamazaki H. Rare but impaired flavin-containing monooxygenase 3 (FMO3) variants reported in a recently updated Japanese mega-databank of genome resources. Drug Metab Pharmacokinet 2024; 55:100539. [PMID: 38280279 DOI: 10.1016/j.dmpk.2023.100539] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 10/18/2023] [Accepted: 11/15/2023] [Indexed: 01/29/2024]
Abstract
Genetic variants of human flavin-containing monooxygenase 3 (FMO3) were investigated using an updated Japanese population panel containing 54,000 subjects (the previous panel contained 38,000 subjects). One stop codon mutation and six amino acid-substituted FMO3 variants were newly identified in the updated databank. Of these, two substituted variants (p.Thr329Ala and p.Arg492Trp) were previously identified in compound haplotypes with p.[(Glu158Lys; Glu308Gly)] and were associated with the metabolic disorder trimethylaminuria. Three recombinant FMO3 protein variants (p.Ser137Leu, p.Ala334Val, and p.Ile426Val) expressed in bacterial membranes had similar activities toward trimethylamine N-oxygenation (∼75-125 %) as wild-type FMO3 (117 min-1); however, the recombinant novel FMO3 variant Phe313Ile showed moderately decreased FMO3 catalytic activity (∼20 % of wild-type). Because of the known deleterious effects of FMO3 C-terminal stop codons, the novel truncated FMO3 Gly184Ter variant was suspected to be inactive. To easily identify the four impaired FMO3 variants (one stop codon mutation and three amino-acid substitutions) in the clinical setting, simple confirmation methods for these FMO3 variants are proposed using polymerase chain reaction/restriction fragment length polymorphism or allele-specific PCR methods. The updated whole-genome sequence data and kinetic analyses revealed that four of the seven single-nucleotide nonsense or missense FMO3 variants had moderately or severely impaired activity toward trimethylamine N-oxygenation.
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Affiliation(s)
| | | | - Eiji Hishinuma
- Advanced Research Center for Innovations in Next-Generation Medicine and Tohoku Medical Megabank Organization, Sendai, Japan
| | - Sakae Saito
- Advanced Research Center for Innovations in Next-Generation Medicine and Tohoku Medical Megabank Organization, Sendai, Japan
| | - Masahiro Hiratsuka
- Advanced Research Center for Innovations in Next-Generation Medicine and Tohoku Medical Megabank Organization, Sendai, Japan; Graduate School of Pharmaceutical Sciences, Tohoku University and Department of Pharmaceutical Sciences, Tohoku University Hospital, Sendai, Japan
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2
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Maksymiuk KM, Szudzik M, Samborowska E, Chabowski D, Konop M, Ufnal M. Mice, rats, and guinea pigs differ in FMOs expression and tissue concentration of TMAO, a gut bacteria-derived biomarker of cardiovascular and metabolic diseases. PLoS One 2024; 19:e0297474. [PMID: 38266015 PMCID: PMC10807837 DOI: 10.1371/journal.pone.0297474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2023] [Accepted: 01/06/2024] [Indexed: 01/26/2024] Open
Abstract
INTRODUCTION Increased plasma trimethylamine oxide (TMAO) is observed in cardiovascular and metabolic diseases, originating from the gut microbiota product, trimethylamine (TMA), via flavin-containing monooxygenases (FMOs)-dependent oxidation. Numerous studies have investigated the association between plasma TMAO and various pathologies, yet limited knowledge exists regarding tissue concentrations of TMAO, TMAO precursors, and interspecies variability. METHODS Chromatography coupled with mass spectrometry was employed to evaluate tissue concentrations of TMAO and its precursors in adult male mice, rats, and guinea pigs. FMO mRNA and protein levels were assessed through PCR and Western blot, respectively. RESULTS Plasma TMAO levels were similar among the studied species. However, significant differences in tissue concentrations of TMAO were observed between mice, rats, and guinea pigs. The rat renal medulla exhibited the highest TMAO concentration, while the lowest was found in the mouse liver. Mice demonstrated significantly higher plasma TMA concentrations compared to rats and guinea pigs, with the highest TMA concentration found in the mouse renal medulla and the lowest in the rat lungs. FMO5 exhibited the highest expression in mouse liver, while FMO3 was highly expressed in rats. Guinea pigs displayed low expression of FMOs in this tissue. CONCLUSION Despite similar plasma TMAO levels, mice, rats, and guinea pigs exhibited significant differences in tissue concentrations of TMA, TMAO, and FMO expression. These interspecies variations should be considered in the design and interpretation of experimental studies. Furthermore, these findings may suggest a diverse importance of the TMAO pathway in the physiology of the evaluated species.
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Affiliation(s)
- Klaudia M. Maksymiuk
- Laboratory of the Centre for Preclinical Research, Department of Experimental Physiology and Pathophysiology, Medical University of Warsaw, Warsaw, Poland
| | - Mateusz Szudzik
- Laboratory of the Centre for Preclinical Research, Department of Experimental Physiology and Pathophysiology, Medical University of Warsaw, Warsaw, Poland
| | - Emilia Samborowska
- Mass spectrometry Laboratory, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - Dawid Chabowski
- Laboratory of the Centre for Preclinical Research, Department of Experimental Physiology and Pathophysiology, Medical University of Warsaw, Warsaw, Poland
| | - Marek Konop
- Laboratory of the Centre for Preclinical Research, Department of Experimental Physiology and Pathophysiology, Medical University of Warsaw, Warsaw, Poland
| | - Marcin Ufnal
- Laboratory of the Centre for Preclinical Research, Department of Experimental Physiology and Pathophysiology, Medical University of Warsaw, Warsaw, Poland
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3
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Giuriato D, Correddu D, Catucci G, Di Nardo G, Bolchi C, Pallavicini M, Gilardi G. Design of a H 2 O 2 -generating P450 SPα fusion protein for high yield fatty acid conversion. Protein Sci 2022; 31:e4501. [PMID: 36334042 PMCID: PMC9679977 DOI: 10.1002/pro.4501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2022] [Revised: 10/29/2022] [Accepted: 11/01/2022] [Indexed: 11/07/2022]
Abstract
Sphingomonas paucimobilis' P450SPα (CYP152B1) is a good candidate as industrial biocatalyst. This enzyme is able to use hydrogen peroxide as unique cofactor to catalyze the fatty acids conversion to α-hydroxy fatty acids, thus avoiding the use of expensive electron-donor(s) and redox partner(s). Nevertheless, the toxicity of exogenous H2 O2 toward proteins and cells often results in the failure of the reaction scale-up when it is directly added as co-substrate. In order to bypass this problem, we designed a H2 O2 self-producing enzyme by fusing the P450SPα to the monomeric sarcosine oxidase (MSOX), as H2 O2 donor system, in a unique polypeptide chain, obtaining the P450SPα -polyG-MSOX fusion protein. The purified P450SPα -polyG-MSOX protein displayed high purity (A417 /A280 = 0.6) and H2 O2 -tolerance (kdecay = 0.0021 ± 0.000055 min-1 ; ΔA417 = 0.018 ± 0.001) as well as good thermal stability (Tm : 59.3 ± 0.3°C and 63.2 ± 0.02°C for P450SPα and MSOX domains, respectively). The data show how the catalytic interplay between the two domains can be finely regulated by using 500 mM sarcosine as sacrificial substrate to generate H2 O2 . Indeed, the fusion protein resulted in a high conversion yield toward fat waste biomass-representative fatty acids, that is, lauric acid (TON = 6,800 compared to the isolated P450SPα TON = 2,307); myristic acid (TON = 6,750); and palmitic acid (TON = 1,962).
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Affiliation(s)
- Daniele Giuriato
- Department of Life Sciences and Systems BiologyUniversity of TorinoTorinoItaly
| | - Danilo Correddu
- Department of Life Sciences and Systems BiologyUniversity of TorinoTorinoItaly
| | - Gianluca Catucci
- Department of Life Sciences and Systems BiologyUniversity of TorinoTorinoItaly
| | - Giovanna Di Nardo
- Department of Life Sciences and Systems BiologyUniversity of TorinoTorinoItaly
| | - Cristiano Bolchi
- Dipartimento di Scienze FarmaceuticheUniversità degli Studi di MilanoMilanItaly
| | - Marco Pallavicini
- Dipartimento di Scienze FarmaceuticheUniversità degli Studi di MilanoMilanItaly
| | - Gianfranco Gilardi
- Department of Life Sciences and Systems BiologyUniversity of TorinoTorinoItaly
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4
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Catucci G, Turella S, Cheropkina H, De Angelis M, Gilardi G, Sadeghi SJ. Green production of indigo and indirubin by an engineered Baeyer–Villiger monooxygenase. BIOCATALYSIS AND AGRICULTURAL BIOTECHNOLOGY 2022. [DOI: 10.1016/j.bcab.2022.102458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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5
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Ernst S, Mährlein A, Ritzmann NH, Drees SL, Fetzner S. A comparative study of
N
‐hydroxylating flavoprotein monooxygenases reveals differences in kinetics and cofactor binding. FEBS J 2022; 289:5637-5655. [DOI: 10.1111/febs.16444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 02/21/2022] [Accepted: 03/18/2022] [Indexed: 12/01/2022]
Affiliation(s)
- Simon Ernst
- Institute of Molecular Microbiology and Biotechnology University of Münster Germany
| | - Almuth Mährlein
- Institute of Molecular Microbiology and Biotechnology University of Münster Germany
| | - Niklas H. Ritzmann
- Institute of Molecular Microbiology and Biotechnology University of Münster Germany
| | - Steffen L. Drees
- Institute of Molecular Microbiology and Biotechnology University of Münster Germany
| | - Susanne Fetzner
- Institute of Molecular Microbiology and Biotechnology University of Münster Germany
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6
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Jing L, Zhang H, Xiang Q, Shen L, Guo X, Zhai C, Hu H. Targeting Trimethylamine N-Oxide: A New Therapeutic Strategy for Alleviating Atherosclerosis. Front Cardiovasc Med 2022; 9:864600. [PMID: 35770223 PMCID: PMC9235870 DOI: 10.3389/fcvm.2022.864600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 05/16/2022] [Indexed: 11/13/2022] Open
Abstract
Atherosclerosis (AS) is one of the most common cardiovascular diseases (CVDs), and there is currently no effective drug to reverse its pathogenesis. Trimethylamine N-oxide (TMAO) is a metabolite of the gut flora with the potential to act as a new risk factor for CVD. Many studies have shown that TMAO is involved in the occurrence and development of atherosclerotic diseases through various mechanisms; however, the targeted therapy for TMAO remains controversial. This article summarizes the vital progress made in relation to evaluations on TMAO and AS in recent years and highlights novel probable approaches for the prevention and treatment of AS.
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Affiliation(s)
- Lele Jing
- Department of Cardiology, The Affiliated Hospital of Jiaxing University, Jiaxing, China
| | - Honghong Zhang
- School of Clinical Medicine, Zhejiang Chinese Medical University, Hangzhou, China
| | - Qiannan Xiang
- School of Clinical Medicine, Zhejiang Chinese Medical University, Hangzhou, China
| | - Liang Shen
- Department of Cardiology, The Affiliated Hospital of Jiaxing University, Jiaxing, China
| | - Xiaoxia Guo
- Department of Cardiology, The Affiliated Hospital of Jiaxing University, Jiaxing, China
| | - Changlin Zhai
- Department of Cardiology, The Affiliated Hospital of Jiaxing University, Jiaxing, China
| | - Huilin Hu
- Department of Cardiology, The Affiliated Hospital of Jiaxing University, Jiaxing, China
- *Correspondence: Huilin Hu
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Flavin-Containing Monooxygenase 3 (FMO3) Is Critical for Dioxin-Induced Reorganization of the Gut Microbiome and Host Insulin Sensitivity. Metabolites 2022; 12:metabo12040364. [PMID: 35448550 PMCID: PMC9029240 DOI: 10.3390/metabo12040364] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 03/18/2022] [Accepted: 04/07/2022] [Indexed: 02/07/2023] Open
Abstract
Exposure to some environmental pollutants can have potent endocrine-disrupting effects, thereby promoting hormone imbalance and cardiometabolic diseases such as non-alcoholic fatty liver disease (NAFLD), diabetes, and cardiorenal diseases. Recent evidence also suggests that many environmental pollutants can reorganize the gut microbiome to potentially impact these diverse human diseases. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is among the most potent endocrine-disrupting dioxin pollutants, yet our understanding of how TCDD impacts the gut microbiome and systemic metabolism is incompletely understood. Here, we show that TCDD exposure in mice profoundly stimulates the hepatic expression of flavin-containing monooxygenase 3 (Fmo3), which is a hepatic xenobiotic metabolizing enzyme that is also responsible for the production of the gut microbiome-associated metabolite trimethylamine N-oxide (TMAO). Interestingly, an enzymatic product of FMO3 (TMAO) has been associated with the same cardiometabolic diseases that these environmental pollutants promote. Therefore, here, we examined TCDD-induced alterations in the gut microbiome, host liver transcriptome, and glucose tolerance in Fmo3+/+ and Fmo3-/- mice. Our results show that Fmo3 is a critical component of the transcriptional response to TCDD, impacting the gut microbiome, host liver transcriptome, and systemic glucose tolerance. Collectively, this work uncovers a previously underappreciated role for Fmo3 in integrating diet-pollutant-microbe-host interactions.
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8
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Catucci G, Ciaramella A, Di Nardo G, Zhang C, Castrignanò S, Gilardi G. Molecular Lego of Human Cytochrome P450: The Key Role of Heme Domain Flexibility for the Activity of the Chimeric Proteins. Int J Mol Sci 2022; 23:ijms23073618. [PMID: 35408976 PMCID: PMC8998974 DOI: 10.3390/ijms23073618] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 03/22/2022] [Accepted: 03/24/2022] [Indexed: 02/04/2023] Open
Abstract
The cytochrome P450 superfamily are heme-thiolate enzymes able to carry out monooxygenase reactions. Several studies have demonstrated the feasibility of using a soluble bacterial reductase from Bacillus megaterium, BMR, as an artificial electron transfer partner fused to the human P450 domain in a single polypeptide chain in an approach known as ‘molecular Lego’. The 3A4-BMR chimera has been deeply characterized biochemically for its activity, coupling efficiency, and flexibility by many different biophysical techniques leading to the conclusion that an extension of five glycines in the loop that connects the two domains improves all the catalytic parameters due to improved flexibility of the system. In this work, we extend the characterization of 3A4-BMR chimeras using differential scanning calorimetry to evaluate stabilizing role of BMR. We apply the ‘molecular Lego’ approach also to CYP19A1 (aromatase) and the data show that the activity of the chimeras is very low (<0.003 min−1) for all the constructs tested with a different linker loop length: ARO-BMR, ARO-BMR-3GLY, and ARO-BMR-5GLY. Nevertheless, the fusion to BMR shows a remarkable effect on thermal stability studied by differential scanning calorimetry as indicated by the increase in Tonset by 10 °C and the presence of a cooperative unfolding process driven by the BMR protein domain. Previously characterized 3A4-BMR constructs show the same behavior of ARO-BMR constructs in terms of thermal stabilization but a higher activity as a function of the loop length. A comparison of the ARO-BMR system to 3A4-BMR indicates that the design of each P450-BMR chimera should be carefully evaluated not only in terms of electron transfer, but also for the biophysical constraints that cannot always be overcome by chimerization.
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9
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Yang Z, Stemmer PM, Petriello MC. Proteomics-Based Identification of Interaction Partners of the Xenobiotic Detoxification Enzyme FMO3 Reveals Involvement in Urea Cycle. TOXICS 2022; 10:60. [PMID: 35202247 PMCID: PMC8877285 DOI: 10.3390/toxics10020060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 01/18/2022] [Accepted: 01/25/2022] [Indexed: 02/06/2023]
Abstract
The hepatic xenobiotic metabolizing enzyme flavin-containing monooxygenase 3 (FMO3) has been implicated in the development of cardiometabolic disease primarily due to its enzymatic product trimethylamine-N oxide (TMAO), which has recently been shown to be associated with multiple chronic diseases, including kidney and coronary artery diseases. Although TMAO may have causative roles as a pro-inflammatory mediator, the possibility for roles in metabolic disease for FMO3, irrespective of TMAO formation, does exist. We hypothesized that FMO3 may interact with other proteins known to be involved in cardiometabolic diseases and that modulating the expression of FMO3 may impact on these interaction partners. Here, we combine a co-immunoprecipitation strategy coupled to unbiased proteomic workflow to report a novel protein:protein interaction network for FMO3. We identified 51 FMO3 protein interaction partners, and through gene ontology analysis, have identified urea cycle as an enriched pathway. Using mice deficient in FMO3 on two separate backgrounds, we validated and further investigated expressional and functional associations between FMO3 and the identified urea cycle genes. FMO3-deficient mice showed hepatic overexpression of carbamoylphosphate synthetase (CPS1), the rate-limiting gene of urea cycle, and increased hepatic urea levels, especially in mice of FVB (Friend leukemia virus B strain) background. Finally, overexpression of FMO3 in murine AML12 hepatocytes led to downregulation of CPS1. Although there is past literature linking TMAO to urea cycle, this is the first published work showing that FMO3 and CPS1 may directly interact, implicating a role for FMO3 in chronic kidney disease irrespective of TMAO formation.
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Affiliation(s)
- Zhao Yang
- Institute of Environmental Health Sciences, Wayne State University, Detroit, MI 48202, USA; (Z.Y.); (P.M.S.)
| | - Paul M. Stemmer
- Institute of Environmental Health Sciences, Wayne State University, Detroit, MI 48202, USA; (Z.Y.); (P.M.S.)
- Department of Pharmaceutical Sciences, College of Pharmacy, Wayne State University, Detroit, MI 48202, USA
| | - Michael C. Petriello
- Institute of Environmental Health Sciences, Wayne State University, Detroit, MI 48202, USA; (Z.Y.); (P.M.S.)
- Department of Pharmacology, School of Medicine, Wayne State University, Detroit, MI 48202, USA
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10
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Shimizu M, Mizugaki A, Koibuchi N, Sango H, Uenuma Y, Yamazaki H. A series of simple detection systems for genetic variants of flavin-containing monooxygenase 3 (FMO3) with impaired function in Japanese subjects. Drug Metab Pharmacokinet 2021; 41:100420. [PMID: 34634752 DOI: 10.1016/j.dmpk.2021.100420] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 07/31/2021] [Accepted: 09/01/2021] [Indexed: 12/30/2022]
Abstract
Increasing numbers of single-nucleotide substitutions of the human flavin-containing monooxygenase 3 (FMO3) gene are being recorded in mega-databases. Phenotype-gene analyses revealed impaired FMO3 variants associated with the metabolic disorder trimethylaminuria. Here, a series of reliable FMO3 genotyping confirmation methods was assembled and developed for 45 impaired FMO3 variants, mainly found in Japanese populations, using singleplex or duplex polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) methods and singleplex, duplex, or tetraplex allele-specific PCR methods. Nine PCR-RFLP procedures with single restriction enzymes and fourteen duplex PCR-RFLP procedures (for p.Trp41Ter and p.Thr329Ala, p.Met66Val and p.Leu163Pro, p.Pro70Leu and p.Glu308Gly, p.Asn114Ser and p.Ser195Leu, p.Glu158Lys and p.Ile441Thr, p.Cys197Ter and p.Trp388Ter, p.Arg205Cys and p.Val257Met, p.Arg205His and p.Cys397Ser, p.Met211ArgfsTer10 and p.Arg492Trp, p.Arg223Gln and p.Leu473Pro, p.Met260Val and p.Thr488Ala, p.Tyr269His and p.Ala311Pro, p.Ser310Leu and p.Gly376Glu, and p.Gln470Ter and p.Arg500Ter) were newly established along with eight singleplex (for p.Pro153GlnfsTer14, p.Gly191Cys, p.Pro248Thr, p.Ile486Met, and p.Pro496Ser, among others), one duplex (p.Ile199Ser and p.Asp286Tyr), and one tetraplex (p.Ile7Thr, p.Val58Ile, p.Thr201Lys, and p.Gly421Val) allele-specific PCR systems. This series of systems should facilitate the easy detection in a clinical setting of FMO3 variants in Japanese subjects susceptible to low drug clearances or drug reactions possibly caused by impaired FMO3 function.
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Affiliation(s)
- Makiko Shimizu
- Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Tokyo, Japan
| | - Ami Mizugaki
- Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Tokyo, Japan
| | - Natsumi Koibuchi
- Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Tokyo, Japan
| | - Haruna Sango
- Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Tokyo, Japan
| | - Yumi Uenuma
- Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Tokyo, Japan
| | - Hiroshi Yamazaki
- Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Tokyo, Japan.
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11
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Cheropkina H, Catucci G, Marucco A, Fenoglio I, Gilardi G, Sadeghi SJ. Human flavin-containing monooxygenase 1 and its long-sought hydroperoxyflavin intermediate. Biochem Pharmacol 2021; 193:114763. [PMID: 34509493 DOI: 10.1016/j.bcp.2021.114763] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 09/03/2021] [Accepted: 09/07/2021] [Indexed: 01/22/2023]
Abstract
Out of the five isoforms of human flavin-containing monooxygenase (hFMO), FMO1 and FMO3 are the most relevant to Phase I drug metabolism. They are involved in the oxygenation of xenobiotics including drugs and pesticides using NADPH and FAD as cofactors. Majority of the characterization of these enzymes has involved hFMO3, where intermediates of its catalytic cycle have been described. On the other hand, research efforts have so far failed in capturing the same key intermediate that is responsible for the monooxygenation activity of hFMO1. In this work we demonstrate spectrophotometrically the formation of a highly stable C4a-hydroperoxyflavin intermediate of hFMO1 upon reduction by NADPH and in the presence of O2. The measured half-life of this flavin intermediate revealed it to be stable and not fully re-oxidized even after 30 min at 15 °C in the absence of substrate, the highest stability ever observed for a human FMO. In addition, the uncoupling reactions of hFMO1 show that this enzyme is <1% uncoupled in the presence of substrate, forming small amounts of H2O2 with no observable superoxide as confirmed by EPR spin trapping experiments. This behaviour is different from hFMO3, that is shown to form both H2O2 and superoxide anion radical as a result of ∼50% uncoupling. These data are consistent with the higher stability of the hFMO1 intermediate in comparison to hFMO3. Taken together, these data demonstrate the different behaviours of these two closely related enzymes with consequences for drug metabolism as well as possible toxicity due to reactive oxygen species.
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Affiliation(s)
- Hanna Cheropkina
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - Gianluca Catucci
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - Arianna Marucco
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | | | - Gianfranco Gilardi
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - Sheila J Sadeghi
- Department of Life Sciences and Systems Biology, University of Torino, Italy.
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12
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Bortolussi S, Catucci G, Gilardi G, Sadeghi SJ. N- and S-oxygenation activity of truncated human flavin-containing monooxygenase 3 and its common polymorphic variants. Arch Biochem Biophys 2020; 697:108663. [PMID: 33152328 DOI: 10.1016/j.abb.2020.108663] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 10/26/2020] [Accepted: 10/30/2020] [Indexed: 02/07/2023]
Abstract
Human flavin-containing monooxygenase 3 (FMO3) is a membrane-bound, phase I drug metabolizing enzyme. It is highly polymorphic with some of its variants demonstrating differences in rates of turnover of its substrates: xenobiotics including drugs as well as dietary compounds. In order to measure its in vitro activity and compare any differences between the wild type enzyme and its polymorphic variants, we undertook a systematic study using different engineered proteins, heterologously expressed in bacteria, purified and catalytically characterized with 3 different substrates. These included the full-length as well as the more soluble C-terminal truncated versions of the common polymorphic variants (E158K, V257M and E308G) of FMO3 in addition to the full-length and truncated wild-type proteins. In vitro activity assays were performed with benzydamine, tamoxifen and sulindac sulfide, whose products were measured by HPLC. Differences in catalytic properties between the wild-type FMO3 and its common polymorphic variants were similar to those observed with the truncated, more soluble versions of the enzymes. Interestingly, the truncated enzymes were better catalysts than the full-length proteins. The data obtained point to the feasibility of using the more soluble forms of this enzyme for in vitro drug assays as well as future biotechnological applications possibly in high throughput systems such as bioelectrochemical platforms and biosensors.
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Affiliation(s)
- Stefania Bortolussi
- Department of Life Sciences and Systems Biology, University of Torino, Italy; School of Health, Sport and Bioscience, University of East London, UK.
| | - Gianluca Catucci
- Department of Life Sciences and Systems Biology, University of Torino, Italy.
| | - Gianfranco Gilardi
- Department of Life Sciences and Systems Biology, University of Torino, Italy.
| | - Sheila J Sadeghi
- Department of Life Sciences and Systems Biology, University of Torino, Italy.
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13
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Catucci G, Aramini D, Sadeghi SJ, Gilardi G. Ligand stabilization and effect on unfolding by polymorphism in human flavin-containing monooxygenase 3. Int J Biol Macromol 2020; 162:1484-1493. [PMID: 32781122 DOI: 10.1016/j.ijbiomac.2020.08.032] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 07/24/2020] [Accepted: 08/04/2020] [Indexed: 12/20/2022]
Abstract
Pharmacogenomics is a powerful tool to prevent adverse reactions caused by different response of individuals to drug administration. Single nucleotide polymorphisms (SNPs) represent up to 90% of genetic variations among individuals. Drug metabolizing enzymes are highly polymorphic therefore the kinetic parameters of their catalytic reactions can be significantly influenced. This work reports on the unfolding process of a phase I drug metabolizing enzyme, human flavin-containing monooxygenase 3 (hFMO3) and its single nucleotide polymorphic variants (SNPs) V257M, E158K and E308G. Differential scanning calorimetry (DSC) indicates that the thermal denaturation of the enzyme is irreversible. The melting temperature (Tm) for the (Wild Type) WT and its polymorphic variants is found to be in a range from 46 °C to 50 °C. Also the activation energies of unfolding (Ea) show no significant differences among all proteins investigated (290-328 KJ/mol), except for the E308G variant that showed a significantly higher Ea of 412 KJ/mol. The presence of the bound NADP+ cofactor is found to stabilize all the variants by shifting the main Tm by 4-5 °C for all the proteins, exception made for E308G where no changes are observed. Isothermal titration calorimetry (ITC) was used to characterize the interaction of the protein with NADP+ in terms of dissociation constant (Kd), enthalpy (ΔH) and entropy (ΔS). Kd values of 1.6 and 0.7 μM, ΔH of -13.9 Kcal/mol and -16.8 Kcal/mol, ΔS of -20.5 cal/mol/deg, and -28.5 cal/mol/deg were found for V257M and E158K respectively. E308G was found to be unable to bind the NADP+ cofactor, a result that is in line with the Tm results. Circular dichroism also confirmed an overall lower stability of E308G, while NADP+ was found to give a strong positive shift of the Tm stabilizing the structure of E158K (46.2 to 50.6 °C). Previous data highlighted significant differences in terms of activity among the SNPs of hFMO3. In this work a minor impact of the SNPs was found on the stability of the enzyme in the ligand free form, except for E308G, whereas the binding of NADP+ reveals major differences among WT and polymorphic variants that are all measurable in terms of heat capacity, enthalpy and secondary structure content. These data provide the first direct evidence of ligand stabilization effects on hFMO3 that can explain the differences observed in catalytic efficiencies and serve as the starting point for the development of inhibitors of this enzyme.
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Affiliation(s)
- G Catucci
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - D Aramini
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - S J Sadeghi
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - G Gilardi
- Department of Life Sciences and Systems Biology, University of Torino, Italy.
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14
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Console L, Scalise M, Mazza T, Pochini L, Galluccio M, Giangregorio N, Tonazzi A, Indiveri C. Carnitine Traffic in Cells. Link With Cancer. Front Cell Dev Biol 2020; 8:583850. [PMID: 33072764 PMCID: PMC7530336 DOI: 10.3389/fcell.2020.583850] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Accepted: 08/31/2020] [Indexed: 12/16/2022] Open
Abstract
Metabolic flexibility is a peculiar hallmark of cancer cells. A growing number of observations reveal that tumors can utilize a wide range of substrates to sustain cell survival and proliferation. The diversity of carbon sources is indicative of metabolic heterogeneity not only across different types of cancer but also within those sharing a common origin. Apart from the well-assessed alteration in glucose and amino acid metabolisms, there are pieces of evidence that cancer cells display alterations of lipid metabolism as well; indeed, some tumors use fatty acid oxidation (FAO) as the main source of energy and express high levels of FAO enzymes. In this metabolic pathway, the cofactor carnitine is crucial since it serves as a “shuttle-molecule” to allow fatty acid acyl moieties entering the mitochondrial matrix where these molecules are oxidized via the β-oxidation pathway. This role, together with others played by carnitine in cell metabolism, underlies the fine regulation of carnitine traffic among different tissues and, within a cell, among different subcellular compartments. Specific membrane transporters mediate carnitine and carnitine derivatives flux across the cell membranes. Among the SLCs, the plasma membrane transporters OCTN2 (Organic cation transport novel 2 or SLC22A5), CT2 (Carnitine transporter 2 or SLC22A16), MCT9 (Monocarboxylate transporter 9 or SLC16A9) and ATB0, + [Sodium- and chloride-dependent neutral and basic amino acid transporter B(0+) or SLC6A14] together with the mitochondrial membrane transporter CAC (Mitochondrial carnitine/acylcarnitine carrier or SLC25A20) are the most acknowledged to mediate the flux of carnitine. The concerted action of these proteins creates a carnitine network that becomes relevant in the context of cancer metabolic rewiring. Therefore, molecular mechanisms underlying modulation of function and expression of carnitine transporters are dealt with furnishing some perspective for cancer treatment.
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Affiliation(s)
- Lara Console
- Unit of Biochemistry and Molecular Biotechnology, Department DiBEST (Biologia, Ecologia, Scienze della Terra), University of Calabria, Arcavacata di Rende, Italy
| | - Mariafrancesca Scalise
- Unit of Biochemistry and Molecular Biotechnology, Department DiBEST (Biologia, Ecologia, Scienze della Terra), University of Calabria, Arcavacata di Rende, Italy
| | - Tiziano Mazza
- Unit of Biochemistry and Molecular Biotechnology, Department DiBEST (Biologia, Ecologia, Scienze della Terra), University of Calabria, Arcavacata di Rende, Italy
| | - Lorena Pochini
- Unit of Biochemistry and Molecular Biotechnology, Department DiBEST (Biologia, Ecologia, Scienze della Terra), University of Calabria, Arcavacata di Rende, Italy
| | - Michele Galluccio
- Unit of Biochemistry and Molecular Biotechnology, Department DiBEST (Biologia, Ecologia, Scienze della Terra), University of Calabria, Arcavacata di Rende, Italy
| | - Nicola Giangregorio
- Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies (IBIOM), National Research Council, Bari, Italy
| | - Annamaria Tonazzi
- Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies (IBIOM), National Research Council, Bari, Italy
| | - Cesare Indiveri
- Unit of Biochemistry and Molecular Biotechnology, Department DiBEST (Biologia, Ecologia, Scienze della Terra), University of Calabria, Arcavacata di Rende, Italy.,Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies (IBIOM), National Research Council, Bari, Italy
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15
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Natural Variation in the ‘Control Loop’ of BVMOAFL210 and Its Influence on Regioselectivity and Sulfoxidation. Catalysts 2020. [DOI: 10.3390/catal10030339] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Baeyer-Villiger monooxygenases (BVMOs) are flavin-dependent enzymes that primarily convert ketones to esters, but can also catalyze heteroatom oxidation. Several structural studies have highlighted the importance of the ‘control loop’ in BVMOs, which adopts different conformations during catalysis. Central to the ‘control loop’ is a conserved tryptophan that has been implicated in NADP(H) binding. BVMOAFL210 from Aspergillus flavus, however, contains a threonine in the equivalent position. Here, we report the structure of BVMOAFL210 in complex with NADP+ in both the ‘open’ and ‘closed’ conformations. In neither conformation does Thr513 contact the NADP+. Although mutagenesis of Thr513 did not significantly alter the substrate scope, changes in peroxyflavin stability and reaction rates were observed. Mutation of this position also brought about changes in the regio- and enantioselectivity of the enzyme. Moreover, lower rates of overoxidation during sulfoxidation of thioanisole were also observed.
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16
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Ciaramella A, Catucci G, Di Nardo G, Sadeghi SJ, Gilardi G. Peroxide-driven catalysis of the heme domain of A. radioresistens cytochrome P450 116B5 for sustainable aromatic rings oxidation and drug metabolites production. N Biotechnol 2020; 54:71-79. [DOI: 10.1016/j.nbt.2019.08.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 08/22/2019] [Accepted: 08/23/2019] [Indexed: 02/08/2023]
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17
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Catucci G, Gao C, Rampolla G, Gilardi G, Sadeghi SJ. Uncoupled human flavin-containing monooxygenase 3 releases superoxide radical in addition to hydrogen peroxide. Free Radic Biol Med 2019; 145:250-255. [PMID: 31580948 DOI: 10.1016/j.freeradbiomed.2019.09.038] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 09/26/2019] [Accepted: 09/29/2019] [Indexed: 11/21/2022]
Abstract
Human flavin-containing monooxygenase 3 (hFMO3) is a drug-metabolizing enzyme capable of performing N- or S-oxidation using the C4a-hydroperoxy intermediate. In this work, we employ both wild type hFMO3 as well as an active site polymorphic variant (N61S) to unravel the uncoupling reactions in the catalytic cycle of this enzyme. We demonstrate that in addition to H2O2 this enzyme also produces superoxide anion radicals as its uncoupling products. The level of uncoupling was found to vary between 50 and 70% (WT) and 90-98% (N61S) for incubations with NADPH and benzydamine over a period of 5 or 20 min, respectively. For the first time, we were able to follow the production of the superoxide radical in hFMO3, which was found to account for 13-18% of the total uncoupling of this human enzyme. Moreover, measurements in the presence or absence of the substrate show that the substrate lowers the level of uncoupling only related to the H2O2 and not the superoxide radical. This is consistent with the entry point of the substrate in this enzyme's catalytic cycle. These findings highlight the importance of the involvement of hFMO3 in the production of radicals in the endoplasmic reticulum, as well as the relevance of single-nucleotide polymorphism leading to deleterious effects of oxidative stress.
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Affiliation(s)
- Gianluca Catucci
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - Chongliang Gao
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - Giulia Rampolla
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - Gianfranco Gilardi
- Department of Life Sciences and Systems Biology, University of Torino, Italy
| | - Sheila J Sadeghi
- Department of Life Sciences and Systems Biology, University of Torino, Italy.
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18
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Gao C, Zheng T. Drug metabolite synthesis by immobilized human FMO3 and whole cell catalysts. Microb Cell Fact 2019; 18:133. [PMID: 31405378 PMCID: PMC6691536 DOI: 10.1186/s12934-019-1189-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Accepted: 08/07/2019] [Indexed: 12/26/2022] Open
Abstract
Background Sufficient reference standards of drug metabolites are required in the drug discovery and development process. However, such drug standards are often expensive or not commercially available. Chemical synthesis of drug metabolite is often difficulty due to the highly regio- and stereo-chemically demanding. The present work aims to construct stable and efficient biocatalysts for the generation of drug metabolites in vitro. Result In this work, using benzydamine as a model drug, two easy-to-perform approaches (whole cell catalysis and enzyme immobilization) were investigated for the synthesis of FMO3-generated drug metabolites. The whole cell catalysis was carried out by using cell suspensions of E. coli JM109 harboring FMO3 and E. coli BL21 harboring GDH (glucose dehydrogenase), giving 1.2 g/L benzydamine N-oxide within 9 h under the optimized conditions. While for another approach, two HisTrap HP columns respectively carrying His6-GDH and His6-FMO3 were connected in series used for the biocatalysis. In this case, 0.47 g/L benzydamine N-oxide was generated within 2.5 h under the optimized conditions. In addition, FMO3 immobilization at the C-terminal (membrane anchor region) significantly improved its enzymatic thermostability by more than 10 times. Moreover, the high efficiency of these two biocatalytic approaches was also confirmed by the N-oxidation of tamoxifen. Conclusions The results presented in this work provides new possibilities for the drug-metabolizing enzymes-mediated biocatalysis. Electronic supplementary material The online version of this article (10.1186/s12934-019-1189-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Chongliang Gao
- Department of Life Sciences and Systems Biology, University of Torino, Via Accademia Albertina 13, 10123, Turin, Italy.
| | - Tingjie Zheng
- Department of Life Sciences and Systems Biology, University of Torino, Via Accademia Albertina 13, 10123, Turin, Italy
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19
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Catucci G, Sadeghi SJ, Gilardi G. A direct time-based ITC approach for substrate turnover measurements demonstrated on human FMO3. Chem Commun (Camb) 2019; 55:6217-6220. [PMID: 31074479 DOI: 10.1039/c9cc01356c] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Transient binding events are a challenging issue in enzymology. Here we demostrate a time-based ITC approach to human flavin-containing monooxygenase 3, an important drug metabolising enzyme. We measure kinetic constants and we demonstrate how this approach can be exploited for measuring the inhibiton of the conversion of the key substrate trimethylamine into trimethylamine N-oxide.
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Affiliation(s)
- Gianluca Catucci
- Department of Life Sciences and Systems Biology, University of Torino, Via Accademia Albertina 13, Torino, 10123, Italy.
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20
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Catucci G, Bortolussi S, Rampolla G, Cusumano D, Gilardi G, Sadeghi SJ. Flavin-Containing Monooxygenase 3 Polymorphic Variants Significantly Affect Clearance of Tamoxifen and Clomiphene. Basic Clin Pharmacol Toxicol 2018; 123:687-691. [DOI: 10.1111/bcpt.13089] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Accepted: 06/25/2018] [Indexed: 01/14/2023]
Affiliation(s)
- Gianluca Catucci
- Department of Life Sciences and Systems Biology; University of Torino; Torino Italy
| | - Stefania Bortolussi
- Department of Life Sciences and Systems Biology; University of Torino; Torino Italy
| | - Giulia Rampolla
- Department of Life Sciences and Systems Biology; University of Torino; Torino Italy
| | - Debora Cusumano
- Department of Life Sciences and Systems Biology; University of Torino; Torino Italy
| | - Gianfranco Gilardi
- Department of Life Sciences and Systems Biology; University of Torino; Torino Italy
| | - Sheila J. Sadeghi
- Department of Life Sciences and Systems Biology; University of Torino; Torino Italy
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21
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Wu X, Li C, Mariyam Z, Jiang P, Zhou M, Zeb F, Haq IU, Chen A, Feng Q. Acrolein-induced atherogenesis by stimulation of hepatic flavin containing monooxygenase 3 and a protection from hydroxytyrosol. J Cell Physiol 2018; 234:475-485. [PMID: 29953618 DOI: 10.1002/jcp.26600] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2017] [Accepted: 03/15/2018] [Indexed: 12/24/2022]
Abstract
Acrolein, a highly toxic α, β-unsaturated aldehyde, promotes the progression of atherosclerosis in association with inflammatory signaling pathway and reverse cholesterol transport (RCT) process. Additionally, hepatic flavin containing monooxygenase 3 (FMO3) is involved in the pathogenesis of atherosclerosis by regulating cholesterol metabolism. Hydroxytyrosol (HT), as a major phenolic compound in olive oil, exerts anti-inflammatory and anti-atherogenic activities in vitro and animal models. The current study was designed to evaluate whether FMO3 participated in pro-atherogenic process by acrolein and HT showed protective effect during this process. Here, endothelial cells and macrophage Raw264.7 cells were used as the cell models. Following oxidized low-density lipoprotein (OX-LDL) treatment, acrolein exposure promoted foam cells formation in macrophage Raw264.7 cells. The expression of FMO3 and inflammatory makers such as phospho-NF-κB, IL-1β, TNFα as well as IL-6 were significantly increased. However, ATP-binding cassette transporters subfamily A member 1 (ABCA1), a major transporter in RCT process, was repressed by acrolein. In addition, FMO3 knockdown could suppress inflammatory markers and promote ABCA1 expression. Hydroxytyrosol (HT) was observed to reduce lipid accumulation, FMO3 expression as well as inflammatory response. Moreover, it promoted ABCA1 expression. Therefore, our findings indicated that acrolein-enhanced atherogenesis by increasing FMO3 which increased inflammatory responses and decreased ABCA1 in vitro can be alleviated by HT, which may have a therapeutic potential for the treatment of atherosclerosis.
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Affiliation(s)
- Xiaoyue Wu
- Department of Nutrition and Food Hygiene, School of Public Health, Nanjing Medical University, Nanjing, China
| | - Chaofeng Li
- Department of Cardiology, The Second Affiliated Hospital of Southeast University, Nanjing, China
| | - Zahula Mariyam
- Department of Nutrition and Food Hygiene, School of Public Health, Nanjing Medical University, Nanjing, China
| | - Pan Jiang
- Department of Nutrition and Food Hygiene, School of Public Health, Nanjing Medical University, Nanjing, China
| | - Ming Zhou
- Department of Nutrition and Food Hygiene, School of Public Health, Nanjing Medical University, Nanjing, China
| | - Falak Zeb
- Department of Nutrition and Food Hygiene, School of Public Health, Nanjing Medical University, Nanjing, China
| | - Ijaz Ul Haq
- Department of Nutrition and Food Hygiene, School of Public Health, Nanjing Medical University, Nanjing, China
| | - Aochang Chen
- Department of Nutrition and Food Hygiene, School of Public Health, Nanjing Medical University, Nanjing, China
| | - Qing Feng
- Department of Nutrition and Food Hygiene, School of Public Health, Nanjing Medical University, Nanjing, China
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22
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Binding of methimazole and NADP(H) to human FMO3: In vitro and in silico studies. Int J Biol Macromol 2018; 118:460-468. [PMID: 29959003 DOI: 10.1016/j.ijbiomac.2018.06.104] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Revised: 06/06/2018] [Accepted: 06/22/2018] [Indexed: 01/10/2023]
Abstract
Human flavin-containing monooxygenase isoform 3 (hFMO3) is an important hepatic drug-metabolizing enzyme, catalyzing the monooxygenation of nucleophilic heteroatom-containing xenobiotics. Based on the structure of bacterial FMO, it is proposed that a conserved asparagine is involved in both NADP(H) and substrate binding. In order to explore the role of this amino acid in hFMO3, two mutants were constructed. In the case of N61Q, increasing the steric hindrance above the flavin N5-C4a causes poor NADP(H) binding, destabilizing the catalytic FAD intermediate, whereas the introduction of a negatively charged residue, N61D, interferes mainly with catalytic intermediate formation and its stability. To better understand the substrate-enzyme interaction, in vitro as well as in silico experiments were carried out with methimazole as substrate. Methimazole is a high-affinity substrate of hFMO3 and can competitively suppress the metabolism of other compounds. Our results demonstrate that methimazole Pi-stacks above the isoalloxazine ring of FAD in hFMO3, in a similar way to indole binding to the bacterial FMO. However, for hFMO3 indole is found to act as a non-substrate competitive inhibitor. Finally, understanding the binding mode of methimazole and indole could be advantageous for development of hFMO3 inhibitors, currently investigated as a possible treatment strategy for atherosclerosis.
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