Pharmacology & Therapeutics 85 (2000) 245–249 0163-7258/00/$ – see front matter © 2000 Elsevier Science Inc. All rights reserved. PII: S0163-7258(99)00057-1 Associate editor: D. Shugar Molecular pharmacological characterization of two multidrug transporters in Lactococcus lactis Hendrik W. van Veen*, Monique Putman, Abelardo Margolles, Kanta Sakamoto, Wil N. Konings Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, NL-9751 NN Haren, The Netherlands Abstract The active extrusion of cytotoxic compounds from the cell by multidrug transporters is one of the major causes of failure of chemo- therapeutic treatment of tumor cells and of infections by pathogenic microorganisms. A multidrug transporter in Lactococcus lactis , LmrA, is a member of the ATP-binding cassette superfamily and a bacterial homolog of the human multidrug resistance P-glycoprotein. Another multidrug transporter in Lactococcus lactis , LmrP, belongs to the major facilitator superfamily, and is one example of a rapidly expanding group of secondary multidrug transporters in microorganisms. Thus, LmrA and LmrP are transport proteins with very differ- ent protein structures, which use different mechanisms of energy coupling to transport drugs out of the cell. Surprisingly, both proteins have overlapping specificities for drugs, are inhibited by the same set of modulators, and transport drugs via a similar transport mecha- nism. The structure-function relationships that dictate drug recognition and transport by LmrP and LmrA represent an intriguing area of research. © 2000 Elsevier Science Inc. All rights reserved. Keywords: Multidrug efflux pump; ATP-binding cassette transporter; Secondary transporter; Drug-binding site; LmrA; LmrP Abbreviations: ABC, ATP-binding cassette; LmrA, Lactococcus lactis multidrug pump driven by ATP hydrolysis; LmrP, Lactococcus lactis multidrug pump driven by proton motive force. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 2. Multidrug transporters in Lactococcus lactis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 3. From cells to proteoliposomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 4. Drug specificity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 5. Transport models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 6. Multiple drug-binding sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 7. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 * Corresponding author. Tel.:+31-50-3632158; fax:+31-50-3632154. E-mail address: h.w.van.veen@biol.rug.nl (H.W. van Veen) 1. Introduction The nutritive and therapeutic treatment of farm animals with antibiotics, amounting to one-half of the world’s anti- biotic output, has selected for drug-resistant microorgan- isms that contaminate the food produced (Perreten et al., 1997). Likewise, the selection of drug-resistant pathogenic microorganisms in hospitalized patients with serious infec- tions, such as pneumonia, urinary tract infections, skin in- fections, and bacteremia, generally has been ascribed to the widespread use of antimicrobial agents (Hughes & Tenover, 1997). Besides bacteria, parasitic protozoa are responsible for some of the most devastating and prevalent diseases of humans and domestic animals, such as malaria (Plasmodium spp.) and toxoplasmosis (Toxoplasma spp.) (for a review, see Borst & Ouellette, 1995). Microorganisms can eliminate the drug target in the cell through the alteration or replacement of molecules that are normally bound by the antibiotic (Spratt, 1994). Alterna- tively, microorganisms can reduce the intracellular concen- tration of drugs by (1) synthesizing enzymes that degrade