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

Abstract
The FtsH (HflB) protein of Escherichia coli is a membrane‐bound ATP‐dependent zinc protease. The role(s) of the N‐terminal membrane‐anchoring region of 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 cytoplasm of E. coli, and were purified as soluble proteins. The four longer constructs, which have a second transmembrane segment and the C‐terminal cytoplasmic region in common, retained ATP‐dependent protease activity toward heat‐shock transcription factor σ32, and were found to be homo‐oligomers. In contrast, the shortest construct which has the C‐terminal cytoplasmic 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 homo‐oligomerization.