Characterization of a conserved alpha-helical, coiled-coil motif at the C-terminal domain of the ATP-dependent FtsH (HflB) protease of Escherichia coli

FtsH (HflB) is an ATP-dependent protease found in prokaryotic cells, mitochondria and chloroplasts. Here, we have identified, in the carboxy-terminal region of FtsH (HfIB), a short alpha helix predicted of forming a coiled-coil, leucine zipper, structure. This region appears to be structurally conserved. The presence of the coiled-coil motif in the Escherichia coli FtsH (HflB) was demonstrated by circular dichroism and cross-linking experiments. Mutational analysis showed that three highly conserved leucine residues are essential for FtsH (HfIB) activity in vivo and in vitro. Purified proteins mutated in the conserved leucine residues, were found to be defective in the degradation of E. coli sigma(32) and the bacteriophage lambda CII proteins. In addition, the mutant proteins were defective in the binding of CII The mutations did not interfere with the ATPase activity of FtsH (HflB). Finally, the mutant proteins were found to be more sensitive to trypsin degradation than the wild-type enzyme suggesting that the alpha helical region is an important structural element of FtsH (HflB).