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J. Biol. Chem., Vol. 282, Issue 33, 24284-24293, August 17, 2007

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Identification and Characterization of Vnx1p, a Novel Type of Vacuolar Monovalent Cation/H⁺ Antiporter of Saccharomyces cerevisiae^*

Olivier Cagnac, Marina Leterrier, Mark Yeager, and Eduardo Blumwald¹

From the Department of Plant Sciences, University of California, Davis, California 95616 and Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037

We identified and characterized Vnx1p, a novel vacuolar monovalent cation/H⁺ antiporter encoded by the open reading frame YNL321w from Saccharomyces cerevisiae. Despite the homology of Vnx1p with other members of the CAX (calcium exchanger) family of transporters, Vnx1p is unable to mediate Ca²⁺ transport but is a low affinity Na⁺/H⁺ and K⁺/H⁺ anti-porter with a K_m of 22.4 and 82.2 mM for Na⁺ and K⁺, respectively. Sequence analyses of Vnx1p revealed the absence of key amino acids shown to be essential for Ca²⁺/H⁺ exchange. vnx1 cells displayed growth inhibition when grown in the presence of hygromycin B or NaCl. Vnx1p activity was found in the vacuoles and shown to be dependent on the electrochemical potential gradient of H⁺ generated by the action of the V-type H⁺-ATPase. The presence of Vnx1p at the vacuolar membrane was further confirmed with cells expressing a VNX1::GFP chimeric gene. Similar to Nhx1p, the prevacuolar compartment-bound Na⁺/H⁺ antiporter, the vacuole-bound Vnx1p appears to play roles in the regulation of ion homeostasis and cellular pH.

Received for publication, April 12, 2007 , and in revised form, June 19, 2007.

^* This work was supported by National Science Foundation Grant MCB-0343279. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Plant Sciences, Mail Stop 5, University of California, One Shields Ave., Davis, CA 95616. Tel.: 530-752-4640; Fax: 530-752-2278; E-mail:eblumwald{at}ucdavis.edu.

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