title: Inhibition of InhA activity, but not KasA activity, induces formation of a KasA-containing complex in mycobacteria.
abstract: Isoniazid (INH) remains one of the key drugs used to control tuberculosis, with the enoyl-AcpM reductase InhA being the primary target. However, based on the observation that INH-treated Mycobacterium tuberculosis overproduces KasA, an enzyme involved in the biosynthesis of mycolic acids, and induces the formation of a covalent complex consisting of AcpM, KasA, and INH, it has been proposed that KasA represents the primary target of INH. However, the relevance of this complex to INH action remains obscure. This study was aimed at clarifying the role of InhA and KasA in relation to INH activity. By using anti-KasA antibodies we detected the KasA-containing complex in INH-treated Mycobacterium smegmatis. In addition, INH-treated cells also produced constant levels of KasA that were not sequestered in the complex and presumably were sufficient to ensure mycolic acid biosynthesis. Interestingly, a furA-lacking strain induced the complex at lower concentrations of INH compared with the control strain, whereas higher INH concentrations were necessary to induce the complex in a strain that lacks katG, suggesting that INH needs to be activated by KatG to induce the KasA-containing complex. The InhA inhibitors ethionamide and diazaborine also induced the complex; thus, its formation was not specifically relevant to INH action but was because of InhA inhibition. In addition, in vitro assays using purified InhA and KasA demonstrated that KatG-activated INH, triclosan, and diazaborine inhibited InhA but not KasA activity. Moreover, several thermosensitive InhA mutant strains of M. smegmatis constitutively expressed the KasA-containing complex. This study provides the biochemical and genetic evidence. 1) Only inhibition of InhA, but not KasA, induces the KasA-containing complex. 2) INH is not part of the complex. 3) INH does not target KasA, consistent with InhA being the primary target of INH.
authors.affiliation: Laboratoire des Mécanismes Moléculaires de la Pathogénie Microbienne, INSERM U447, Institut Pasteur de Lille/IBL, Lille, France. laurent.kremer@ibl.fr
authors.forename: Laurent
authors.initials: L
authors.lastname: Kremer
authors.forename: Lynn G
authors.initials: LG
authors.lastname: Dover
authors.forename: Hector R
authors.initials: HR
authors.lastname: Morbidoni
authors.forename: Catherine
authors.initials: C
authors.lastname: Vilchèze
authors.forename: William N
authors.initials: WN
authors.lastname: Maughan
authors.forename: Alain
authors.initials: A
authors.lastname: Baulard
authors.forename: Shiao-Chun
authors.initials: SC
authors.lastname: Tu
authors.forename: Nadine
authors.initials: N
authors.lastname: Honoré
authors.forename: Vojo
authors.initials: V
authors.lastname: Deretic
authors.forename: James C
authors.initials: JC
authors.lastname: Sacchettini
authors.forename: Camille
authors.initials: C
authors.lastname: Locht
authors.forename: William R
authors.initials: WR
authors.lastname: Jacobs
authors.forename: Gurdyal S
authors.initials: GS
authors.lastname: Besra
mesh_terms: D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D000906:Antibodies / Q000494:pharmacology; D000995:Antitubercular Agents / Q000494:pharmacology; D001426:Bacterial Proteins; D004352:Drug Resistance, Microbial; D005000:Ethionamide / Q000494:pharmacology; D007538:Isoniazid / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000378:metabolism; D009154:Mutation; D020102:Mycobacterium smegmatis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000906:Antibodies; D000995:Antitubercular Agents; D001426:Bacterial Proteins; D009097:Multienzyme Complexes; D010088:Oxidoreductases; C085257:InhA protein, Mycobacterium; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase; D005000:Ethionamide; D007538:Isoniazid