DEFECTIVE EXPORT OF A PERIPLASMIC ENZYME DISRUPTS REGULATION OF FATTY-ACID SYNTHESIS

Escherichia coli thioesterase I (TesA) encoded by the tesA gene is located in the cellular periplasm. The tesA gene was modified by deletion of the leader sequence such that the mature enzyme was instead localized to the cellular cytosol. Production of thioesterase I in the cytosol results in striking changes in the pattern of E. coli lipid synthesis. In contrast to normal E. coli cells, cells producing cytosolic TesA synthesize large amounts of free fatty acid at all stages of growth. Moreover, cultures of the cytosolic TesA-producing strain continue lipid synthesis (as free fatty acid) in stationary phase whereas lipid synthesis is normally strongly inhibited in such cultures. Surprisingly, production of cytosolic thioesterase I gave only modest inhibition of membrane phospholipid synthesis. These results demonstrate that internalization of a normally secreted enzyme can disrupt normal cellular regulatory mechanisms.