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J Bacteriol, June 1998, p. 2817-2821, Vol. 180, No. 11
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Paradoxical Enhancement of the Activity of a Bacterial Multidrug Transporter Caused by Substitutions of a Conserved Residue

Katya A. Klyachko and Alexander A. Neyfakh*

Center for Pharmaceutical Biotechnology and Department of Medicinal Chemistry and Pharmacognosy, University of Illinois, Chicago, Illinois 60607

Received 4 February 1998/Accepted 25 March 1998

Substitution of threonine or serine for the evolutionary conserved intramembrane proline P347 of the Bacillus subtilis multidrug transporter Bmr significantly increases the toxin-effluxing activity of Bmr without affecting its abundance in the cell. In cocultivation experiments, we demonstrate that although the mutant T347 Bmr is advantageous to cells growing in the presence of a toxin, the wild-type P347 Bmr is advantageous under the conditions of nutritional limitation. This may explain why Bmr has evolved the way it did, that is, with proline at position 347. These observations provide a basis for speculating that the evolution of Bmr has been determined by its presently unidentified natural function rather than by its ability to expel diverse toxins from the cell.

* Corresponding author. Mailing address: Center for Pharmaceutical Biotechnology (M/C 870), University of Illinois, 900 S. Ashland Ave., Chicago, IL 60607. Phone: (312) 996-7231. Fax: (312) 413-9303. E-mail: neyfakh{at}uic.edu.

J Bacteriol, June 1998, p. 2817-2821, Vol. 180, No. 11
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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Copyright © 1998 by the American Society for Microbiology. All rights reserved.