Institute of Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research, Albert-Ludwigs University, Freiburg, Germany.
Res Microbiol. 2011 Apr;162(3):285-91. doi: 10.1016/j.resmic.2011.01.001. Epub 2011 Feb 1.
Gram-positive soil bacteria Arthrobacter nicotinovorans, Nocardioides sp. JS614 and Rhodococcus opacus were shown to contain similarly organized clusters of homologous genes for nicotine catabolism. An uncharacterized gene of a predicted nitrilase within these gene clusters was cloned from A. nicotinovorans and biochemical data unexpectedly showed that the protein exhibited ω-amidase activity toward α-ketoglutaramate. Structural modelling of the protein suggested the presence of the catalytic triad Cys-Glu-Lys, characteristic of this class of enzymes, and supported α-ketoglutaramate as substrate. A-ketoglutaramate could be generated by hydrolytic cleavage of the C-N bond of the trihydroxypyridine ring produced by nicotine catabolism in these bacteria. This ω-amidase, together with glutamate dehydrogenase, may form a physiologically relevant enzyme couple, leading to transformation of metabolically inert α-ketoglutaramate derived from trihydroxypyridine into glutamate, a central compound of nitrogen metabolism.
土壤革兰氏阳性细菌节杆菌（Arthrobacter nicotinovorans）、诺卡氏菌（Nocardioides sp. JS614）和红球菌（Rhodococcus opacus）被证明含有类似组织的同源基因簇，用于尼古丁代谢。从节杆菌（Arthrobacter nicotinovorans）中克隆了这些基因簇中一个未表征的预测腈酶基因，令人意外的生化数据表明，该蛋白对α-酮戊二酸具有ω-酰胺酶活性。该蛋白的结构建模表明存在催化三联体 Cys-Glu-Lys，这是此类酶的特征，并支持α-酮戊二酸作为底物。α-酮戊二酸可以通过水解这些细菌中尼古丁代谢产生的三羟基吡啶环的 C-N 键生成。这种 ω-酰胺酶与谷氨酸脱氢酶一起，可能形成一个生理相关的酶对，将代谢惰性的三羟基吡啶衍生的α-酮戊二酸转化为谷氨酸，这是氮代谢的中心化合物。
