FtsH (HflB) is an ATP-dependent protease selectively acting on SecY and some other membrane proteins

The FtsH protein is a membrane-bound ATPase of Escherichia coli that was proposed to be involved in membrane protein assembly as well as degradation of some unstable proteins, SecY, a subunit of protein translocase, is FtsH dependently degraded in vivo when it fails to associate with its partner (the SecE protein), We constructed a series of mutants in which mutations were introduced into conserved residues in the two ATP binding consensus sequences or the zinc binding sequence of FtsH, We purified wild-type and mutant FtsH proteins by making use of a polyhistidine tag attached to their carboxyl termini, Complementation analysis and ATPase activity assays in vitro indicated that, of the two sets of ATP binding sequence motifs, the one located C-terminally (Al) is essential for ATPase activity and in two functioning of FtsH, Wild-type FtsH protein degraded purified SecY in an ATP hydrolysis-dependent manner in vitro. Mutant proteins without ATPase activity were inactive in proteolysis. A zinc binding motif mutant showed a decreased proteolytic activity. SecY and FtsH were cross linkable with each other in the membrane, provided that FtsH had an ATPase-inactivating mutation, These results demonstrate that FtsH binds to and degrades SecY, its Al motif and the zinc binding motif being important for the proteolytic activity. FtsH-dependent proteolysis was also demonstrated for SecY in crude membrane extracts, whereas a majority of other membrane proteins were not degraded, indicating that FtsH has high selectivity in protein degradation.