Schühle Karola, Gescher Johannes, Feil Ulrich, Paul Michael, Jahn Martina, Schägger Hermann, Fuchs Georg
Mikrobiologie, Institut für Biologie II, Universität Freiburg, Germany.
J Bacteriol. 2003 Aug;185(16):4920-9. doi: 10.1128/JB.185.16.4920-4929.2003.
In the denitrifying member of the beta-Proteobacteria Thauera aromatica, the anaerobic metabolism of aromatic acids such as benzoate or 2-aminobenzoate is initiated by the formation of the coenzyme A (CoA) thioester, benzoyl-CoA and 2-aminobenzoyl-CoA, respectively. Both aromatic substrates were transformed to the acyl-CoA intermediate by a single CoA ligase (AMP forming) that preferentially acted on benzoate. This benzoate-CoA ligase was purified and characterized as a 57-kDa monomeric protein. Based on V(max)/K(m), the specificity constant for 2-aminobenzoate was 15 times lower than that for benzoate; this may be the reason for the slower growth on 2-aminobenzoate. The benzoate-CoA ligase gene was cloned and sequenced and was found not to be part of the gene cluster encoding the general benzoyl-CoA pathway of anaerobic aromatic metabolism. Rather, it was located in a cluster of genes coding for a novel aerobic benzoate oxidation pathway. In line with this finding, the same CoA ligase was induced during aerobic growth with benzoate. A deletion mutant not only was unable to grow anaerobically on benzoate or 2-aminobenzoate, but also aerobic growth on benzoate was affected. This suggests that benzoate induces a single benzoate-CoA ligase. The product of benzoate activation, benzoyl-CoA, then acts as inducer of separate anaerobic or aerobic pathways of benzoyl-CoA, depending on whether oxygen is lacking or present.
在β-变形菌纲的反硝化菌陶厄氏菌属中,苯甲酸或2-氨基苯甲酸等芳香酸的厌氧代谢分别通过辅酶A(CoA)硫酯即苯甲酰-CoA和2-氨基苯甲酰-CoA的形成而启动。两种芳香底物都通过一种优先作用于苯甲酸的单一CoA连接酶(形成AMP)转化为酰基-CoA中间体。这种苯甲酸-CoA连接酶被纯化并鉴定为一种57 kDa的单体蛋白。根据V(max)/K(m),2-氨基苯甲酸的特异性常数比苯甲酸低15倍;这可能是在2-氨基苯甲酸上生长较慢的原因。苯甲酸-CoA连接酶基因被克隆并测序,发现它不是编码厌氧芳香代谢通用苯甲酰-CoA途径的基因簇的一部分。相反,它位于编码一条新的需氧苯甲酸氧化途径的基因簇中。与此发现一致的是,在用苯甲酸进行需氧生长期间诱导出了相同的CoA连接酶。一个缺失突变体不仅不能在苯甲酸或2-氨基苯甲酸上厌氧生长,而且在苯甲酸上的需氧生长也受到影响。这表明苯甲酸诱导产生一种单一的苯甲酸-CoA连接酶。苯甲酸激活的产物苯甲酰-CoA随后根据是否缺氧分别作为苯甲酰-CoA不同厌氧或需氧途径的诱导剂。