Homologous gene clusters of nicotine catabolism, including a new ω-amidase for α-ketoglutaramate, in species of three genera of Gram-positive bacteria

Gram-positive soil bacteria Arthrobacter nicotinwovorans, 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 nittilase within these gene clusters was do:led from A. nicotinovorans and biochemical data unexpectedly showed that the protein exhibited omega-amidase activity toward alpha-ketoglutaramate. Structural modelling of the protein suggested the presence of the catalytic triad Cys-Glu-Lys, characteristic of this class of enzymes, and supported alpha-ketoglutaramate as substrate. A-ketoglutaratnate could be generated by hydrolytic cleavage of the C-N bond of the trihydroxypyridine ring produced by nicotine catabolism in these bacteria. This to-amidase, together with glutamate dehydrogenase, may form a physiologically relevant enzyme couple, leading to transformation of metabolically inert (x-ketoglutaramate derived from trihydroxypyridine into glutamate, a central compound of nitrogen metabolism. (C) 2011 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.