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

FtsH (HfIB) is an ATP-dependent protease found in prokaryotic cells, mitoch ondria and chloroplasts. Here, we have identified, in the carboxyterminal r egion of FtsH (HfIB), a short alpha helix predicted of forming a coiled-coi l, leucine zipper, structure. This region appears to be structurally conser ved. The presence of the coiled-coil motif in the Escherichia coli FtsH (Hf IB) was demonstrated by circular dichroism and cross-linking experiments. M utational 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 th e degradation of E. coli sigma(32) and the bacteriophage lambda CII protein s. In addition, the mutant proteins were defective in the binding of CII Th e mutations did not interfere with the ATPase activity of FtsH (HfIB). Fina lly, the mutant proteins were found to be more sensitive to trypsin degrada tion than the wild-type enzyme suggesting that the alpha helical region is an important structural element of FtsH (HLIB). (C) 2000 Academic Press.