Membrane-localized protease able to endoproteolytically degrade overproduced SecY but not YccA, another membrane protein. It seems to cleave SecY at specific cytoplasmic sites. Does not require ATP. Its natural substrate has not been identified. Probably plays a role in the quality control of integral membrane proteins. Binds 1 zinc ion per subunit. Bioinformatics programs predict 4 transmembrane helices, however PhoA and Bla fusions as well as other experiments only confirm the first 2. By temperature upshift (by the sigma-32 heat shock transcription factor). Also under control of CpxR. Undergoes self-cleavage. This may not be physiological. No visible phenotype, however one of HtpX or FtsH is essential for cell viability. Belongs to the peptidase M48B family.