Role of the methylcitrate cycle in Mycobacterium tuberculosis metabolism, intracellular growth, and virulence
Role of the methylcitrate cycle in Mycobacterium tuberculosis metabolism, intracellular growth, and virulence
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DOI：
10.1111/j.1365-2958.2006.05155.x
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发表时间：
2006-06-01
影响因子：
3.6
通讯作者：
McKinney, John D.
中科院分区：
文献类型：
--
作者：
Muñoz-Elías, Ernesto J.;Upton, Anna M.;McKinney, John D.
细菌和真菌在脂肪酸基质上的生长需要分解代谢的β -氧化循环和倒伏的乙醛酸循环。由奇链脂肪酸的β -氧化产生的丙酰辅酶a通过甲基柠檬酸循环代谢。结核分枝杆菌具有柠檬酸甲基合成酶（MCS）和柠檬酸甲基脱水酶（MCD）的同源物，但不具有2-甲基异柠檬酸裂解酶（MCL）。虽然mcl与乙醛酸循环的异柠檬酸裂解酶（icl）具有有限的同源性，但这些酶被认为在功能上不重叠。以前我们报道结核分枝杆菌ICL亚型1和2是在脂肪酸、巨噬细胞和小鼠中生长所共同需要的。缺乏icl的细菌不能在丙酸盐上生长，这表明在结核分枝杆菌中，ICL1和ICL2可能在乙氧酸循环中作为icl，在甲基柠檬酸循环中作为mcl。在这里，我们提供生化和遗传证据来支持这一解释。通过构建缺失prpC（编码MCS）和prpD（编码MCD）的突变菌株，进一步评估甲基柠檬酸循环在结核分枝杆菌代谢中的作用。Delta prpDC菌株在体外丙酸培养基和体外感染的小鼠骨髓源性巨噬细胞中均不能生长；通过与含有prpDC的质粒互补，恢复了这些条件下的生长。矛盾的是，在感染野生型或δ prpDC细菌的小鼠中，细菌的生长和持久性以及组织病理学没有区别。
Growth of bacteria and fungi on fatty acid substrates requires the catabolic beta-oxidation cycle and the anaplerotic glyoxylate cycle. Propionyl-CoA generated by beta-oxidation of odd-chain fatty acids is metabolized via the methylcitrate cycle. Mycobacterium tuberculosis possesses homologues of methylcitrate synthase (MCS) and methylcitrate dehydratase (MCD) but not 2-methylisocitrate lyase (MCL). Although MCLs share limited homology with isocitrate lyases (ICLs) of the glyoxylate cycle, these enzymes are thought to be functionally non-overlapping. Previously we reported that the M. tuberculosis ICL isoforms 1 and 2 are jointly required for growth on fatty acids, in macrophages, and in mice. ICL-deficient bacteria could not grow on propionate, suggesting that in M. tuberculosis ICL1 and ICL2 might function as ICLs in the glyoxylate cycle and as MCLs in the methylcitrate cycle. Here we provide biochemical and genetic evidence supporting this interpretation. The role of the methylcitrate cycle in M. tuberculosis metabolism was further evaluated by constructing a mutant strain in which prpC (encoding MCS) and prpD (encoding MCD) were deleted. The Delta prpDC strain could not grow on propionate media in vitro or in murine bone marrow-derived macrophages infected ex vivo; growth under these conditions was restored by complementation with a plasmid containing prpDC. Paradoxically, bacterial growth and persistence, and tissue pathology, were indistinguishable in mice infected with wild-type or Delta prpDC bacteria.