Second transmembrane segment of FtsH plays a role in its proteolytic activity and homo-oligomerization

The FtsH (HflB) protein of Escherichia coli is a membrane-bound ATP-depende nt zinc protease, The role(s) of the N-terminal membrane-anchoring region o f FtsH were studied by fusion with a maltose-binding protein (MBP) at five different N-termini of FtsH, The MBP-FtsH fusions were expressed in the cyt oplasm of E. coli, and were purified as soluble proteins. The four longer c onstructs, which hale a second transmembrane segment and the C-terminal cyt oplasmic region in common, retained ATP-dependent protease activity toward heat-shock transcription factor sigma(32), and were found to be homo-oligom ers, In contrast, the shortest construct which has the C-terminal cytoplasm ic region but not the second transmembrane segment showed neither protease activity nor oligomerization. Therefore, the second transmembrane segment, which neighbors the C-terminal cytoplasmic region of the FtsH, participates in not only its membrane-anchoring, but also its protease activity and hom ooligomerization. (C) 1999 Federation of European Biochemical Societies.