Pollas

Published December 8, 2008

JCB: ARTICLE

Plasma membrane microdomains regulate turnover of transport proteins in yeast
Guido Grossmann,1 Jan Malinsky,2 Wiebke Stahlschmidt,1 Martin Loibl,1 Ina Weig-Meckl,1 Wolf B. Frommer,4 Miroslava Opekarová,3 and Widmar Tanner1
1 2

Institute of Cell Biology and Plant Physiology, University of Regensburg, 93053 Regensburg, Germany Institute ofExperimental Medicine and 3Institute of Microbiology, Academy of Sciences of the Czech Republic, 14220 Prague, Czech Republic 4 Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305

THE JOURNAL OF CELL BIOLOGY

I

n this study, we investigate whether the stable segregation of proteins and lipids within the yeast plasma membrane serves a particular biological function.We show that 21 proteins cluster within or associate with the ergosterol-rich membrane compartment of Can1 (MCC). However, proteins of the endocytic machinery are excluded from MCC. In a screen, we identified 28 genes affecting MCC appearance and found that genes involved in lipid biosynthesis and vesicle transport are significantly overrepresented. Deletion of Pil1, a component of eisosomes,

orof Nce102, an integral membrane protein of MCC, results in the dissipation of all MCC markers. These deletion mutants also show accelerated endocytosis of MCCresident permeases Can1 and Fur4. Our data suggest that release from MCC makes these proteins accessible to the endocytic machinery. Addition of arginine to wild-type cells leads to a similar redistribution and increased turnover of Can1.Thus, MCC represents a protective area within the plasma membrane to control turnover of transport proteins.

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Introduction
The plasma membrane of fungal cells is laterally compartmented. Various membrane proteins fused to GFP are organized in specific surface patterns, whereas others are distributed homogeneously. Bagnat and Simons (2002)observed that Fus1-GFP, Gas1-derived GFP-glycosylphosphatidylinositol, and ergosterol are clustered at the tip of the shmoo, the mating projection of Saccharomyces cerevisiae. Proteins destined to the tip of the shmoo partition into this compartment and are thus retained and segregated from the rest of the membrane. Wachtler et al. (2003) reported that sterols are localized in distinct regions of theplasma membrane of Schizosaccharomyces pombe in a cell cycle–dependent manner. Membrane sterols are detected at the septum, the site of cell division, and at the growing tips. The phenomenon of sterol-rich domains in yeast plasma membrane was reviewed in Alvarez et al. (2007). Our earlier studies (Malínská et al., 2003, 2004; Grossmann et al., 2007) show that the plasma membrane proteins in S.cerevisiae are distributed in at least three different modes: either they are concentrated in discrete patches, each patch being 300 nm in diameter, they occupy a mesh-shaped compartment, which spreads between
Correspondence to Miroslava Opekarová: opekaro@biomed.cas.cz; or Widmar Tanner: sekretariat.tanner@biologie.uni-regensburg.de Abbreviations used in this paper: LiAc, lithium acetate; MCC,membrane compartment of Can1; mRFP, monomeric red fluorescent protein.

the patches, or they are homogenously dispersed throughout these two areas. The patchy compartment called membrane compartment of Can1 (MCC) contains, in addition to the arginine transporter Can1, two other proton symporters, Fur4 and Tat2, and three tetraspan proteins of unknown function, Sur7, Fmp45, and Ynl194c (Young et al.,2002; Malínská et al., 2003, 2004; Grossmann et al., 2007). In the mesh-shaped membrane compartment of Pma1, only the most abundant plasma membrane protein, the H+-ATPase, has been localized so far (Malínská et al., 2003). Finally, Hxt1 and Gap1 represent proteins that are homogenously distributed within the plasma membrane (Malínská et al., 2003; Lauwers et al., 2007). In close vicinity to the...