Metabolic Instability of Escherichia coli Cyclopropane Fatty Acid Synthase Is Due to RpoH-Dependent Proteolysis
AbstractMetabolic Instability of Escherichia coli Cyclopropane Fatty Acid Synthase Is Due to RpoH-Dependent Proteolysis Ying-Ying Chang 1 , Johannes Eichel 2 , and John E. Cronan Jr. 1 , 3 , * Departments of Microbiology 1 and Biochemistry, 3 University of Illinois, Urbana, Illinois 61801, and Hans-Knöll Institute for Natural Products Research, 07745 Jena, Germany 2 ABSTRACT Cyclopropane fatty acids (CFAs) are generally synthesized as bacterial cultures enter stationary phase. In Escherichia coli , the onset of CFA synthesis results from increased transcription of cfa , the gene encoding CFA synthase. However, the increased level of CFA synthase activity is transient; the activity quickly declines to the basal level. We report that the loss of CFA activity is due to proteolytic degradation dependent on expression of the heat shock regulon. CFA synthase degradation is unaffected by mutations in the lon , clpP , and groEL genes or by depletion of the intracellular ATP pools. It seems likely that CFA synthase is the target of an unidentified energy-independent heat shock regulon protease. This seems to be the first example of heat shock-dependent degradation of a normal biosynthetic enzyme.