Slayden R A, Lee R E, Barry C E
Tuberculosis Research Section, Twinbrook II, Room 239, Laboratory of Host Defenses,12441 Parklawn Drive, NIAID, Rockville, MD 20852, USA.
Mol Microbiol. 2000 Nov;38(3):514-25. doi: 10.1046/j.1365-2958.2000.02145.x.
Genetic and biochemical evidence has implicated two different target enzymes for isoniazid (INH) within the unique type II fatty acid synthase (FAS) system involved in the production of mycolic acids. These two components are an enoyl acyl carrier protein (ACP) reductase, InhA, and a beta-ketoacyl-ACP synthase, KasA. We compared the consequences of INH treatment of Mycobacterium tuberculosis (MTB) with two inhibitors having well-defined targets: triclosan (TRC), which inhibits InhA; and thiolactomycin (TLM), which inhibits KasA. INH and TLM, but not TRC, upregulate the expression of an operon containing five FAS II components, including kasA and acpM. Although all three compounds inhibit mycolic acid synthesis, treatment with INH and TLM, but not with TRC, results in the accumulation of ACP-bound lipid precursors to mycolic acids that were 26 carbons long and fully saturated. TLM-resistant mutants of MTB were more cross-resistant to INH than TRC-resistant mutants. Overexpression of KasA conferred more resistance to TLM and INH than to TRC. Overexpression of InhA conferred more resistance to TRC than to INH and TLM. Co-overexpression of both InhA and KasA resulted in strongly enhanced levels of INH resistance, in addition to cross-resistance to both TLM and TRC. These results suggest that these components of the FAS II complex are not independently regulated and that alterations in the expression level of InhA affect expression levels of KasA. Nonetheless, INH appeared to resemble TLM more closely in overall mode of action, and KasA levels appeared to be tightly correlated with INH sensitivity.
遗传和生化证据表明，在参与分枝菌酸生成的独特II型脂肪酸合酶（FAS）系统中，异烟肼（INH）有两种不同的靶标酶。这两种成分是烯酰酰基载体蛋白（ACP）还原酶InhA和β-酮酰-ACP合酶KasA。我们将结核分枝杆菌（MTB）用INH处理的结果与两种具有明确靶标的抑制剂进行了比较：抑制InhA的三氯生（TRC）；以及抑制KasA的硫霉素（TLM）。INH和TLM，但不是TRC，上调了一个包含五个FAS II成分（包括kasA和acpM）的操纵子的表达。尽管所有三种化合物都抑制分枝菌酸的合成，但用INH和TLM处理，而不是用TRC处理，会导致与26个碳长且完全饱和的分枝菌酸结合的ACP脂质前体积累。MTB的TLM抗性突变体比TRC抗性突变体对INH的交叉抗性更强。KasA的过表达赋予对TLM和INH的抗性比对TRC的抗性更强。InhA的过表达赋予对TRC的抗性比对INH和TLM的抗性更强。InhA和KasA的共过表达除了对TLM和TRC产生交叉抗性外，还导致INH抗性水平大幅提高。这些结果表明，FAS II复合物的这些成分不是独立调节的，并且InhA表达水平的改变会影响KasA的表达水平。尽管如此，INH在总体作用模式上似乎更类似于TLM，并且KasA水平似乎与INH敏感性密切相关。
