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Clp-Dependent Proteolysis Down-Regulates Central Metabolic Pathways in Glucose-Starved Bacillus subtilis ^,

Institute of Microbiology, Ernst-Moritz-Arndt-University, 17487 Greifswald, Germany,¹ Friedrich-Loeffler-Institute, Federal Research Institute for Animal Health, Boddenblick 5a, 17493 Greifswald-Insel Riems, Germany,² Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9751 NN Haren, The Netherlands,³ Department of Biochemistry, University of Illinois, 600 South Mathews, Urbana, Illinois 61801⁴

Received 31 July 2007/ Accepted 23 October 2007

Entry into stationary phase in Bacillus subtilis is linked not only to a redirection of the gene expression program but also to posttranslational events such as protein degradation. Using ³⁵S-labeled methionine pulse-chase labeling and two-dimensional polyacrylamide gel electrophoresis we monitored the intracellular proteolysis pattern during glucose starvation. Approximately 200 protein spots diminished in the wild-type cells during an 8-h time course. The degradation rate of at least 80 proteins was significantly reduced in clpP, clpC, and clpX mutant strains. Enzymes of amino acid and nucleotide metabolism were overrepresented among these Clp substrate candidates. Notably, several first-committed-step enzymes for biosynthesis of aromatic and branched-chain amino acids, cell wall precursors, purines, and pyrimidines appeared as putative Clp substrates. Radioimmunoprecipitation demonstrated GlmS, IlvB, PurF, and PyrB to be novel ClpCP targets. Our data imply that Clp proteases down-regulate central metabolic pathways upon entry into a nongrowing state and thus contribute to the adaptation to nutrient starvation. Proteins that are obviously nonfunctional, unprotected, or even "unemployed" seem to be recognized and proteolyzed by Clp proteases when the resources for growth become limited.

Published ahead of print on 2 November 2007.

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