Subunit a of proton ATPase F0 sector is a substrate of the FtsH protease in Escherichia coli

Abstract
Escherichia coli FtsH is a membrane‐bound ATPase with a proteolytic activity against the SecY subunit of protein translocase. We now report that subunit a of the membrane‐embedded F0 part of H+‐ATPase is another substrate of FtsH. Pulse‐chase experiments showed that subunit a is unstable when it alone (without F0 subunits b and c) was oversynthesized and that it is stabilized in the ftsH mutants. Selective and ATP‐dependent degradation of subunit a by purified FtsH protein was demonstrated in vitro. These results suggest that FtsH serves as a quality‐control mechanism to avoid potentially harmful accumulation of free subunit a in the membrane.