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A two-component small multidrug resistance pump functions as a metabolic valve during nicotine catabolism by Arthrobacter nicotinovorans

¹ Institute of Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research, Albrecht-Ludwigs University, Freiburg, Germany
² Institute of Biology III, Albrecht-Ludwigs University, Freiburg, Germany
³ Department of Biochemistry, Alexandru-Ioan-Cuza University, Iasi, Romania

Correspondence
Roderich Brandsch
roderich.brandsch{at}biochemie.uni-freiburg.de

The genes nepAB of a small multidrug resistance (SMR) pump were identified as part of the pAO1-encoded nicotine regulon responsible for nicotine catabolism in Arthrobacter nicotinovorans. When [¹⁴C]nicotine was added to the growth medium the bacteria exported the ¹⁴C-labelled end product of nicotine catabolism, methylamine. In the presence of the proton-motive force inhibitors 2,4-dinitrophenol (DNP), carbonyl cyanide m-chlorophenylhydrazone (CCCP) or the proton ionophore nigericin, export of methylamine was inhibited and radioactivity accumulated inside the bacteria. Efflux of [¹⁴C]nicotine-derived radioactivity from bacteria was also inhibited in a pmfR : cmx strain with downregulated nepAB expression. Because of low amine oxidase levels in the pmfR : cmx strain, -N-methylaminobutyrate, the methylamine precursor, accumulated. Complementation of this strain with the nepAB genes, carried on a plasmid, restored the efflux of nicotine breakdown products. Both NepA and NepB were required for full export activity, indicating that they form a two-component efflux pump. NepAB may function as a metabolic valve by exporting methylamine, the end product of nicotine catabolism, and, in conditions under which it accumulates, the intermediate -N-methylaminobutyrate.

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				P. Ganas and R. Brandsch Uptake of L-nicotine and of 6-hydroxy-L-nicotine by Arthrobacter nicotinovorans and by Escherichia coli is mediated by facilitated diffusion and not by passive diffusion or active transport Microbiology, June 1, 2009; 155(6): 1866 - 1877. [Abstract] [Full Text] [PDF]