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J. Biol. Chem., Vol. 280, Issue 11, 10435-10443, March 18, 2005

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A Dictyostelium Mutant with Reduced Lysozyme Levels Compensates by Increased Phagocytic Activity^*

Iris Müller, Ninon ubert, Heike Otto, Rosa Herbst¶||, Harald Rühling, Markus Maniak**, and Matthias Leippe

From the Department of Cell Biology, Kassel University, Heinrich-Plett-Strasse 40, 34132 Kassel, Bernhard Nocht Institute for Tropical Medicine, Bernhard-Nocht-Strasse 74, 20359 Hamburg, ^¶Department of Special Zoology, Ruhr University of Bochum, Universitätsstrasse 150, 44780 Bochum, and Zoological Institute of the University of Kiel, Olshausenstrasse 40, 24098 Kiel, Germany

Lysozymes are bacteria-degrading enzymes and play a major role in the immune defense of animals. In free-living protozoa, lysozyme-like proteins are involved in the digestion of phagocytosed bacteria. Here, we purified a protein with lysozyme activity from Dictyostelium amoebae, which constitutes the founding member, a novel class of lysozymes. By tagging the protein with green fluorescent protein or the Myc epitope, a new type of lysozyme-containing vesicle was identified that was devoid of other known lysosomal enzymes. The most highly expressed isoform, encoded by the alyA gene, was knocked out by homologous recombination. The mutant cells had greatly reduced enzymatic activity and grew inefficiently when bacteria were the sole food source. Over time the mutant gained the ability to internalize bacteria more efficiently, so that the defect in digestion was compensated by increased uptake of food particles.

Received for publication, October 7, 2004 , and in revised form, December 28, 2004.

^* This work was supported by the Deutsche Forschungsgemeinschaft Grants MA 1439/4-1 and LE 1075/2-3. 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.

^|| Recipient of a Lise Meitner fellowship from Nordrhein-Westfalen.

^** To whom correspondence should be addressed: Abt. Zellbiologie, Universität Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany. Tel.: 49-561-804-4798; Fax: 49-561-804-4592; E-mail: maniak{at}uni-kassel.de.

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