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Powering the ABC Multidrug Exporter LmrA: How Nucleotides Embrace the Ion-Motive Force

Powering the ABC Multidrug Exporter LmrA: How Nucleotides Embrace the Ion-Motive Force

Kelvin Agboh, Calvin H F Lau, Yvonne S K Khoo, Himansha Singh, Sagar Raturi, Asha V Nair, Julie Howard, Marco Chiapello, Renata Feret, Michael J Deery, Satoshi Murakami, Hendrik W van Veen

Sci Adv. 2018 Sep 19;4(9):eaas9365.

PMID: 30255140

Abstract:

LmrA is a bacterial ATP-binding cassette (ABC) multidrug exporter that uses metabolic energy to transport ions, cytotoxic drugs, and lipids. Voltage clamping in a Port-a-Patch was used to monitor electrical currents associated with the transport of monovalent cationic HEPES+ by single-LmrA transporters and ensembles of transporters. In these experiments, one proton and one chloride ion are effluxed together with each HEPES+ ion out of the inner compartment, whereas two sodium ions are transported into this compartment. Consequently, the sodium-motive force (interior negative and low) can drive this electrogenic ion exchange mechanism in cells under physiological conditions. The same mechanism is also relevant for the efflux of monovalent cationic ethidium, a typical multidrug transporter substrate. Studies in the presence of Mg-ATP (adenosine 5'-triphosphate) show that ion-coupled HEPES+ transport is associated with ATP-bound LmrA, whereas ion-coupled ethidium transport requires ATP binding and hydrolysis. HEPES+ is highly soluble in a water-based environment, whereas ethidium has a strong preference for residence in the water-repelling plasma membrane. We conclude that the mechanism of the ABC transporter LmrA is fundamentally related to that of an ion antiporter that uses extra steps (ATP binding and hydrolysis) to retrieve and transport membrane-soluble substrates from the phospholipid bilayer.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP7365459	HEPES		7365-45-9	Price

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