The Saccharomyces cerevisiae Weak-Acid-Inducible ABC Transporter Pdr12 Transports Fluorescein and Preservative Anions from the Cytosol by an Energy-Dependent Mechanism

ABSTRACT Growth of Saccharomyces cerevisiae in the presence of the weak-acid preservative sorbic acid results in the induction of the ATP-binding cassette (ABC) transporter Pdr12 in the plasma membrane (P. Piper, Y. Mahe, S. Thompson, R. Pandjaitan, C. Holyoak, R. Egner, M. Muhlbauer, P. Coote, and K. Kuchler, EMBO J. 17:4257–4265, 1998). Pdr12 appears to mediate resistance to water-soluble, monocarboxylic acids with chain lengths of from C1 to C7. Exposure to acids with aliphatic chain lengths greater than C7 resulted in no observable sensitivity ofΔpdr12 mutant cells compared to the parent. Parent andΔpdr12 mutant cells were grown in the presence of sorbic acid and subsequently loaded with fluorescein. Upon addition of an energy source in the form of glucose, parent cells immediately effluxed fluorescein from the cytosol into the surrounding medium. In contrast, under the same conditions, cells of the Δpdr12 mutant were unable to efflux any of the dye. When both parent andΔpdr12 mutant cells were grown without sorbic acid and subsequently loaded with fluorescein, upon the addition of glucose no efflux of fluorescein was detected from either strain. Thus, we have shown that Pdr12 catalyzes the energy-dependent extrusion of fluorescein from the cytosol. Lineweaver-Burk analysis revealed that sorbic and benzoic acids competitively inhibited ATP-dependent fluorescein efflux. Thus, these data provide strong evidence that sorbate and benzoate anions compete with fluorescein for a putative monocarboxylate binding site on the Pdr12 transporter.