PMID:7592810

Citation	Bolhuis, H, Poelarends, G, van Veen, HW, Poolman, B, Driessen, AJ and Konings, WN (1995) The Lactococcal lmrP gene encodes a proton motive force-dependent drug transporter. J. Biol. Chem. 270:26092-8
Abstract	To genetically dissect the drug extrusion systems of Lactococcus lactis, a chromosomal DNA library was made in Escherichia coli and recombinant strains were selected for resistance to high concentrations of ethidium bromide. Recombinant strains were found to be resistant not only to ethidium bromide but also to daunomycin and tetraphenylphosphonium. The drug resistance is conferred by the lmrP gene, which encodes a hydrophobic polypeptide of 408 amino acid residues with 12 putative membrane-spanning segments. Some sequence elements in this novel membrane protein share similarity to regions in the transposon Tn10-encoded tetracycline resistance determinant TetA, the multidrug transporter Bmr from Bacillus subtilis, and the bicyclomycin resistance determinant Bcr from E. coli. Drug resistance associated with lmrP expression correlated with energy-dependent extrusion of the molecules. Drug extrusion was inhibited by ionophores that dissipate the proton motive force but not by the ATPase inhibitor ortho-vanadate. These observations are indicative for a drug-proton antiport system. A lmrP deletion mutant was constructed via homologous recombinant using DNA fragments of the flanking region of the gene. The L. lactis (delta lmrP) strain exhibited residual ethidium extrusion activity, which in contrast to the parent strain was inhibited by ortho-vanadate. The results indicate that in the absence of the functional drug-proton anti-porter LmrP, L. lactis is able to overexpress another, ATP-dependent, drug extrusion system. These findings substantiate earlier studies on the isolation and characterization of drug-resistant mutants of L. lactis (Bolhuis, H., Molenaar, D., Poelarends, G., van Veen, H. W., Poolman, B., Driessen, A. J. M., and Konings, W. N. (1994) J. Bacteriol. 176, 6957-6964).
Links	PubMed
Keywords	Amino Acid Sequence; Bacterial Proteins; Base Sequence; Biological Transport; Carrier Proteins/biosynthesis; Carrier Proteins/chemistry; Carrier Proteins/genetics; Chromosomes, Bacterial; Cloning, Molecular; DNA, Bacterial/metabolism; Drug Resistance, Microbial/genetics; Escherichia coli; Ethidium/metabolism; Ethidium/pharmacology; Gene Library; Genes, Bacterial; Lactococcus lactis/genetics; Lactococcus lactis/metabolism; Membrane Proteins/biosynthesis; Membrane Proteins/chemistry; Membrane Proteins/genetics; Membrane Transport Proteins; Models, Structural; Molecular Sequence Data; Plasmids; Polymerase Chain Reaction; Protein Structure, Secondary; Recombinant Proteins/biosynthesis; Restriction Mapping
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
9LACT:Q48658		GO:0042891: antibiotic transport	ECO:0000315:		P		Figure 3: The graph displays the growth of E. coli depends upon the expression of the lmrP gene.	complete

References

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