Characterization of the Escherichia coli AaeAB efflux pump: a metabolic relief valve?
Treatment of Escherichia coli with p-hydroxybenzoic acid (pHBA) resulted in upregulation of yhcP, encoding a protein of the putative efflux protein family. Also upregulated were the adjacent genes yhcQ, encoding a protein of the membrane fusion protein family, and yhcR, encoding a small protein without a known or suggested function. The function of the upstream, divergently transcribed gene yhcS, encoding a regulatory protein of the LysR family, in regulating expression of yhcRQP was shown. Furthermore, it was demonstrated that several aromatic carboxylic acid compounds serve as inducers of yhcRQP expression. The efflux function encoded by yhcP was proven by the hypersensitivity to pHBA of a yhcP mutant strain. A yhcS mutant strain was also hypersensitive to pHBA. Expression of yhcQ and yhcP was necessary and sufficient for suppression of the pHBA hypersensitivity of the yhcS mutant. Only a few aromatic carboxylic acids of hundreds of diverse compounds tested were defined as substrates of the YhcQP efflux pump. Thus, we propose renaming yhcS, yhcR, yhcQ, and yhcP, to reflect their role in aromatic carboxylic acid efflux, to aaeR, aaeX, aaeA, and aaeB, respectively. The role of pHBA in normal E. coli metabolism and the highly regulated expression of the AaeAB efflux system suggests that the physiological role may be as a "metabolic relief valve" to alleviate toxic effects of imbalanced metabolism.
DuPont Company CR&D, Rt. 141 and Powdermill Road, P.O. Box 80173, Wilmington, DE 19880-0173, USA. Tina.K.Van-Dyk@usa.dupont.com
Tina K
TK
Van Dyk
Lori J
LJ
Templeton
Keith A
KA
Cantera
Pamela L
PL
Sharpe
F Sima
FS
Sariaslani
D001692:Biological Transport; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D008826:Microbial Sensitivity Tests; D020411:Oligonucleotide Array Sequence Analysis; D009876:Operon; D010226:Parabens / Q000378:metabolism* / Q000494:pharmacology*; D013379:Substrate Specificity
D029968:Escherichia coli Proteins; D010226:Parabens; C038193:4-hydroxybenzoic acid