{"title":"The coenzyme B<sub>12</sub> precursor 5,6-dimethylbenzimidazole is a flavin antagonist in <i>Salmonella</i>.","authors":"Lahiru Malalasekara, Jorge C Escalante-Semerena","doi":"10.15698/mic2023.09.803","DOIUrl":null,"url":null,"abstract":"<p><p><i>Salmonella enterica</i> subsp. <i>enterica</i> sv. Typhimurium str. LT2 (hereafter <i>S.</i> Typhimurium) synthesizes adenosylcobalamin (AdoCbl, CoB<sub>12</sub>) <i>de novo</i> only under anoxic conditions, but it can assemble the lower ligand loop (a.k.a. the nucleotide loop) and can form the unique C-Co bond present in CoB<sub>12</sub> in the presence or absence of molecular oxygen. During studies of nucleotide loop assembly in <i>S.</i> Typhimurium, we noticed that the growth of this bacterium could be arrested by the lower ligand nucleobase, namely 5,6-dimethylbenzimidazole (DMB). Here we report <i>in vitro</i> and <i>in vivo</i> evidence that shows that the structural similarity of DMB to the isoalloxazine moiety of flavin cofactors causes its deleterious effect on cell growth. We studied DMB inhibition of the housekeeping flavin dehydrogenase (Fre) and three flavoenzymes that initiate the catabolism of tricarballylate, succinate or D-alanine in <i>S.</i> Typhimurium. Notably, while growth with tricarballylate was inhibited by 5-methyl-benzimidazole (5-Me-Bza) and DMB, growth with succinate or glycerol was arrested by DMB but not by 5-Me-Bza. Neither unsubstituted benzimidazole nor adenine inhibited growth of <i>S.</i> Typhimurium at DMB inhibitory concentrations. Whole genome sequencing analysis of spontaneous mutant strains that grew in the presence of inhibitory concentrations of DMB identified mutations effecting the <i>cycA</i> (encodes D-Ala/D-Ser transporter) and <i>dctA</i> (encodes dicarboxylate transporter) genes and in the coding sequence of the tricarballylate transporter (TcuC), suggesting that increased uptake of substrates relieved DMB inhibition. We discuss two possible mechanisms of inhibition by DMB.</p>","PeriodicalId":18397,"journal":{"name":"Microbial Cell","volume":null,"pages":null},"PeriodicalIF":4.1000,"publicationDate":"2023-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10468695/pdf/","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Microbial Cell","FirstCategoryId":"99","ListUrlMain":"https://doi.org/10.15698/mic2023.09.803","RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CELL BIOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Salmonella enterica subsp. enterica sv. Typhimurium str. LT2 (hereafter S. Typhimurium) synthesizes adenosylcobalamin (AdoCbl, CoB12) de novo only under anoxic conditions, but it can assemble the lower ligand loop (a.k.a. the nucleotide loop) and can form the unique C-Co bond present in CoB12 in the presence or absence of molecular oxygen. During studies of nucleotide loop assembly in S. Typhimurium, we noticed that the growth of this bacterium could be arrested by the lower ligand nucleobase, namely 5,6-dimethylbenzimidazole (DMB). Here we report in vitro and in vivo evidence that shows that the structural similarity of DMB to the isoalloxazine moiety of flavin cofactors causes its deleterious effect on cell growth. We studied DMB inhibition of the housekeeping flavin dehydrogenase (Fre) and three flavoenzymes that initiate the catabolism of tricarballylate, succinate or D-alanine in S. Typhimurium. Notably, while growth with tricarballylate was inhibited by 5-methyl-benzimidazole (5-Me-Bza) and DMB, growth with succinate or glycerol was arrested by DMB but not by 5-Me-Bza. Neither unsubstituted benzimidazole nor adenine inhibited growth of S. Typhimurium at DMB inhibitory concentrations. Whole genome sequencing analysis of spontaneous mutant strains that grew in the presence of inhibitory concentrations of DMB identified mutations effecting the cycA (encodes D-Ala/D-Ser transporter) and dctA (encodes dicarboxylate transporter) genes and in the coding sequence of the tricarballylate transporter (TcuC), suggesting that increased uptake of substrates relieved DMB inhibition. We discuss two possible mechanisms of inhibition by DMB.