Novel Localization of a Na+/H+ Exchanger in a Late Endosomal Compartment of Yeast

doi:10.1074/jbc.273.33.21054

Novel Localization of a Na⁺/H⁺ Exchanger in a Late Endosomal Compartment of Yeast

IMPLICATIONS FOR VACUOLE BIOGENESIS*

Richard Nass and
Rajini Rao‡

From the Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

Abstract

Na⁺/H⁺ exchangers catalyze the electrically silent countertransport of Na⁺and H⁺, controlling the transmembrane movement of salt, water, and acid-base equivalents, and are therefore critical for Na⁺ tolerance, cell volume control, and pH regulation. In contrast to numerous well studied plasma membrane isoforms (NHE1–4), much less is known about intracellular Na⁺/H⁺ exchangers, and thus far no vertebrate isoform has been shown to have an exclusively endosomal distribution. In this context, we show that the yeast NHE homologue, Nhx1 (Nass, R., Cunningham, K. W., and Rao, R. (1997) J. Biol. Chem.272, 26145–26152), localizes uniquely to prevacuolar compartments, equivalent to late endosomes of animal cells. In living yeast, we show that these compartments closely abut the vacuolar membrane in a striking bipolar distribution, suggesting that vacuole biogenesis occurs at distinct sites. Nhx1 is the founding member of a newly emergent cluster of exchanger homologues, from yeasts, worms, and humans that may share a common intracellular localization. By compartmentalizing Na⁺, intracellular exchangers play an important role in halotolerance; furthermore, we hypothesize that salt and water movement into vesicles may regulate vesicle volume and pH and thus contribute to vacuole biogenesis.

Footnotes

↵* This work was supported by a grant from the National Institutes of Health and an American Cancer Society Junior Faculty Award (to R. R.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ To whom correspondence should be addressed: Dept. of Physiology, The Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore MD 21205. Tel.: 410-955-4732; Fax: 410-955-0461; E-mail:rajini_rao{at}qmail.bs.jhu.edu.
Abbreviations:

kbp

kilobase pair

PCR

polymerase chain reaction

HA

hemagglutinin

GFP

green fluorescent protein

PVC

prevacuolar compartment.
- Received April 30, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.