title: Organic hydroperoxide resistance protein and ergothioneine compensate for loss of mycothiol in Mycobacterium smegmatis mutants.
abstract: The mshA::Tn5 mutant of Mycobacterium smegmatis does not produce mycothiol (MSH) and was found to markedly overproduce both ergothioneine and an ~15-kDa protein determined to be organic hydroperoxide resistance protein (Ohr). An mshA(G32D) mutant lacking MSH overproduced ergothioneine but not Ohr. Comparison of the mutant phenotypes with those of the wild-type strain indicated the following: Ohr protects against organic hydroperoxide toxicity, whereas ergothioneine does not; an additional MSH-dependent organic hydroperoxide peroxidase exists; and elevated isoniazid resistance in the mutant is associated with both Ohr and the absence of MSH. Purified Ohr showed high activity with linoleic acid hydroperoxide, indicating lipid hydroperoxides as the likely physiologic targets. The reduction of oxidized Ohr by NADH was shown to be catalyzed by lipoamide dehydrogenase and either lipoamide or DlaT (SucB). Since free lipoamide and lipoic acid levels were shown to be undetectable in M. smegmatis, the bound lipoyl residues of DlaT are the likely source of the physiological dithiol reductant for Ohr. The pattern of occurrence of homologs of Ohr among bacteria suggests that the ohr gene has been distributed by lateral transfer. The finding of multiple Ohr homologs with various sequence identities in some bacterial genomes indicates that there may be multiple physiologic targets for Ohr proteins.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0314, USA.
authors.forename: Philong
authors.initials: P
authors.lastname: Ta
authors.forename: Nancy
authors.initials: N
authors.lastname: Buchmeier
authors.forename: Gerald L
authors.initials: GL
authors.lastname: Newton
authors.forename: Mamta
authors.initials: M
authors.lastname: Rawat
authors.forename: Robert C
authors.initials: RC
authors.lastname: Fahey
mesh_terms: D000995:Antitubercular Agents / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000235:genetics*; D003545:Cysteine / Q000096:biosynthesis*; D004251:DNA Transposable Elements; D024881:Drug Resistance, Bacterial; D004880:Ergothioneine / Q000378:metabolism*; D006020:Glycopeptides / Q000096:biosynthesis*; D006861:Hydrogen Peroxide / Q000633:toxicity; D007294:Inositol / Q000096:biosynthesis*; D007538:Isoniazid / Q000378:metabolism; D050296:Microbial Viability / Q000187:drug effects; D016254:Mutagenesis, Insertional; D020102:Mycobacterium smegmatis / Q000187:drug effects* / Q000235:genetics
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D006020:Glycopeptides; C089265:mycothiol; D007294:Inositol; D006861:Hydrogen Peroxide; D004880:Ergothioneine; D003545:Cysteine; D007538:Isoniazid