Acts as a processive, ATP-dependent zinc metallopeptidase for both cytoplasmic and membrane proteins. Plays a role in the quality control of integral membrane proteins. Degrades a few membrane proteins that have not been assembled into complexes such as SecY, F(0) ATPase subunit a and YccA, and also cytoplasmic proteins sigma-32, LpxC, KdtA and phage lambda cII protein among others. Degrades membrane proteins in a processive manner starting at either the N- or C-terminus; recognition requires a cytoplasmic tail of about 20 residues with no apparent sequence requirements. It presumably dislocates membrane-spanning and periplasmic segments of the protein into the cytoplasm to degrade them, this probably requires ATP. Degrades C-terminal-tagged cytoplasmic proteins which are tagged with an 11-amino-acid nonpolar destabilizing tail via a mechanism involving the 10SA (SsrA) stable RNA. As FtsH regulates the levels of both LpxC and KdtA it is required for synthesis of both the protein and lipid components of lipopolysaccharide (LPS). (Microbial infection) Probably transports the toxic C-terminal region of CdiA from E.coli strain 536, E.cloacae strain ATCC 13047 and of Y.pestis strain A across the inner membrane to the cytoplasm, where CdiA has a toxic effect. Toxin transport is strain-specific, mutations in this gene do not confer resistance to several other tested CdiA toxins. Binds 1 zinc ion per subunit. (Microbial infection) Activity against phage lambda cII protein is inhibited by EDTA but not by PMSF. In vitro pre-incubation of FtsH with HflKC abolishes its activity against phage lambda cII protein at the cytoplasmic side of the membrane. The E.coli AAA domain has been modeled as a homohexamer, in Thermus thermophilus the same domain crystallizes as a homohexamer. Forms a complex with HflKC (formerly called HflA); complex formation is stimulated by ATP. Interacts with YccA, and probably weakly with QmcA. Can be cross-linked to YidC (OxaA) and to a nascent polypeptide chain for an integral membrane protein. Lethality, due to increased levels of LpxC, which increases the level of LPS in the cell and results in formation of abnormal membrane structures in the periplasm. Lethality is suppressed under conditions in which LPS synthesis is reduced (PubMed:10048027). Disruption confers resistance to cellular contact-dependent growth inhibition (CDI) CdiA of E.coli strain 536, E.cloacae strain ATCC 13047 and of Y.pestis strain A, but not to CdiA from E.coli strain 93 toxin (PubMed:26305955). The ftsH gene was discovered independently through 3 different phenotypes and received 3 different names: ftsH, for filamentous temperature-sensitive; tolZ, for colicin tolerance, and hlfB, because mutants show a high frequency of lysogenization when infected with phage lambda. Requires ATP for protease catalytic activity, probably due to tight coupling of the 2 activities; ADP or non-hydrolyzable analogs cannot substitute, except when unfolded, non-physiological substrates are tested. In the central section; belongs to the AAA ATPase family. In the C-terminal section; belongs to the peptidase M41 family. Glu-476 was identified as the third Zn ligand (PubMed:11827531), however in other crystal structures (Aquifex aeolicus and Thermotoga maritima) the conserved equivalent residue does not bind Zn. Instead it makes a hydrogen bond with the side chain of the first catalytic Zn-binding residue and indirectly stabilizes the Zn. Extended N-terminus.