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J. Biol. Chem., Vol. 280, Issue 39, 33289-33297, September 30, 2005

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Microautophagic Vacuole Invagination Requires Calmodulin in a Ca²⁺-independent Function^*

Andreas Uttenweiler, Heinz Schwarz, and Andreas Mayer1

From the Département de Biochimie, Université de Lausanne, Chemin des Boveresses 155, 1066 Epalinges, Switzerland and the Max-Planck-Institut für Entwicklungsbiologie, Spemannstrasse 35, 72076 Tübingen, Germany

Microautophagy is the uptake of cytosolic compounds by direct invagination of the vacuolar/lysosomal membrane. In Saccharomyces cerevisiae microautophagic uptake of soluble cytosolic proteins occurs via an autophagic tube, a highly specialized vacuolar membrane invagination. Autophagic tubes are topologically equivalent to the invaginations at multivesicular endosomes. At the tip of an autophagic tube, vesicles (autophagic bodies) pinch off into the vacuolar lumen for degradation. In this study we have identified calmodulin (Cmd1p) as necessary for microautophagy. Temperature-sensitive mutants for Cmd1p displayed reduced frequencies of vacuolar tube formation and/or abnormal tube morphologies. Microautophagic vacuole invagination was sensitive to Cmd1p antagonists as well as to antibodies to Cmd1p. cmd1 mutants with substitutions in the Ca²⁺-binding domains showed full invagination activity, and vacuolar membrane invagination was independent of the free Ca²⁺ concentration. Thus, rather than acting as a calcium-triggered switch, Cmd1p has a constitutive Ca²⁺-independent role in the formation of autophagic tubes. Kinetic analysis indicates that calmodulin is required for autophagic tube formation rather than for the final scission of vesicles from the tip of the tube.

Received for publication, June 3, 2005 , and in revised form, July 28, 2005.

^* This work was supported by Deutsche Forschungsgemeinschaft Grant SFB466-A10 and grants from Bundesministerium für Bildung und Forschung, Schweizerischer Nationalfonds, and the Boehringer Ingelheim Foundation (to A. M.) and a grant from the Boehringer Ingelheim Fonds (to A. U.). 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: Dépt. de Biochimie, Université de Lausanne, Chemin des Boveresses 155, 1066 Epalinges, Switzerland. Tel.: 41-21-692-5704; Fax: 41-21-692-5705; E-mail: andreas.mayer{at}unil.ch.

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This article has been cited by other articles:

				A. Uttenweiler, H. Schwarz, H. Neumann, and A. Mayer The Vacuolar Transporter Chaperone (VTC) Complex Is Required for Microautophagy Mol. Biol. Cell, January 1, 2007; 18(1): 166 - 175. [Abstract] [Full Text] [PDF]