Format

Send to

Choose Destination
FASEB J. 2005 Oct;19(12):1698-700. Epub 2005 Jul 22.

A critical role of a carboxylate in proton conduction by the ATP-binding cassette multidrug transporter LmrA.

Author information

1
Department of Pharmacology, University of Cambridge, Cambridge, UK.

Abstract

The ATP binding cassette (ABC) transporter LmrA from the bacterium Lactococcus lactis is a homolog of the human multidrug resistance P-glycoprotein (ABCB1), the activity of which impairs the efficacy of chemotherapy. In a previous study, LmrA was shown to mediate ethidium efflux by an ATP-dependent proton-ethidium symport reaction in which the carboxylate E314 is critical. The functional importance of this key residue for ABC proteins was suggested by its conservation in a wider family of related transporters; however, the structural basis of its role was not apparent. Here, we have used homology modeling to define the structural environment of E314. The residue is nested in a hydrophobic environment that probably elevates its pKa, accounting for the pH dependency of drug efflux that we report in this work. Functional analyses of wild-type and mutant proteins in cells and proteoliposomes support our proposal for the mechanistic role of E314 in proton-coupled ethidium transport. As the carboxylate is known to participate in proton translocation by secondary-active transporters, our observations suggest that this substituent can play a similar role in the activity of ABC transporters.

PMID:
16040836
DOI:
10.1096/fj.04-3558fje
[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Atypon
Loading ...
Support Center