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J. Biol. Chem., Vol. 279, Issue 6, 4498-4506, February 6, 2004
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Inhibition of Sodium/Proton Exchange by a Rab-GTPase-activating Protein Regulates Endosomal Traffic in Yeast*
From the Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
Endosomal Na+/H+ exchangers are important for salt and osmotolerance, vacuolar pH regulation, and endosomal trafficking. We show that the C terminus of yeast Nhx1 interacts with Gyp6, a GTPase-activating protein for the Ypt/Rab family of GTPases, and that Gyp6 colocalizes with Nhx1 in the endosomal/prevacuolar compartment (PVC). The gyp6 null mutant exhibits novel phenotypes consistent with loss of negative regulation of Nhx1, including increased tolerance to hygromycin, increased vacuolar pH, and decreased plasma membrane potential. In contrast, overexpression of Gyp6 increases sensitivity to hygromycin, decreases vacuolar pH, and results in a slight missorting of vacuolar carboxypeptidase Y to the cell surface. We conclude that Gyp6 is a negative regulator of Nhx1-dependent trafficking out of the PVC. Taken together with its GTPase-activating protein-dependent role as a negative regulator of Ypt6-mediated retrograde traffic to the Golgi, we propose that Gyp6 coordinates upstream and downstream events in the PVC to Golgi pathway. Our findings provide a possible molecular link between intraendosomal pH and regulation of vesicular trafficking.
Received for publication, July 11, 2003 , and in revised form, November 3, 2003.
* This work was supported by National Institutes of Health Grant DK54214 (to R. R.). 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.
Predoctoral fellow of the American Heart Association, Mid-Atlantic Affiliate.
To whom correspondence should be addressed: Dept. of Physiology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205. Tel.: 410-955-4732; Fax: 410-955-0461; E-mail: rrao{at}jhmi.edu.
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