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First published online 14 February 2006
doi: 10.1242/jcs.02808

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Acidic clusters target transmembrane proteins to the contractile vacuole in Dictyostelium cells

¹ Université de Genève, Centre Médical Universitaire, Département de Physiologie Cellulaire et Métabolisme, CH-1211 Genève 4, Switzerland
² IFR 128 BioSciences Lyon-Gerland, Institut de Biologie et Chimie des Protéines, UMR5086–CNRS/Université Lyon I, 7 Passage du Vercors, 69367 Lyon CEDEX 07, France

^* Author for correspondence (e-mail: f.letourneur{at}ibcp.fr)

Accepted 24 November 2005

The mechanisms responsible for the targeting of transmembrane integral proteins to the contractile vacuole (CV) network in Dictyostelium discoideum are unknown. Here we show that the transfer of the cytoplasmic domain of a CV-resident protein (Rh50) to a reporter transmembrane protein (CsA) is sufficient to address the chimera (CsA-Rh50) to the CV. We identified two clusters of acidic residues responsible for this targeting, and these motifs interacted with the -adaptin AP-1 subunit in a yeast protein-protein interaction assay. For the first time we report the existence of an indirect transport pathway from the plasma membrane to the CV via endosomes. Upon internalization, the small fraction of CsA-Rh50 present at the cell surface was first concentrated in endosomes distinct from early and late p80-positive endosomes and then slowly transported to the CV. Together our results suggest the existence of an AP-1-dependent selective transport to the contractile vacuole in Dictyostelium.

Key words: Contractile vacuole, Endosomes, Sorting signals, Clathrin-adaptor, Dictyostelium discoideum