The C-terminal end of LpxC is required for degradation by the FtsH protease

Lipopolysaccharide (LPS) biosynthesis is essential in Gram negative bacteria. LpxC, the key enzyme in LPS formation, catalyses the limiting reaction and controls the ratio between LPS and phospholipids. As overproduction of LPS is toxic, the cellular amount of LpxC must be regulated carefully. The membrane-bound protease FtsH controls the level of LpxC via proteolysis making FtsH the only essential protease of Escherichia coli. We found that the chaperones DnaK and DnaJ co-purified with LpxC. However, degradation of LpxC was DnaK/J-independent in contrast to turnover of the heat shock sigma factor sigma32 (RpoH). The stability of LpxC in a bacterial one-hybrid system suggested that a terminus of LpxC might be important for degradation. Different LpxC truncations and extensions were constructed. Removal of at least five amino acids from the C-terminus abolished degradation by FtsH in vivo. While addition of two aspartic acids to LpxC did not alter its half-life, the exchange of the last two residues against aspartic acids resulted in stabilization. All stable LpxC enzymes were active in vivo as assayed by their high toxicity. Our data demonstrate that the C-terminus of LpxC contains a signal sequence necessary for FtsH-dependent degradation.