Membrane insertion of F 0 c subunit of F 0 F 1 ATPase depends on glycolipozyme MPIase and is stimulated by YidC.

The F0 c subunit of F0 F1 ATPase (F0 -c) possesses two membrane-spanning stretches with N- and C-termini exposed to the periplasmic (extracellular) side of the cytoplasmic membrane of E. coli. Although F0 -c insertion has been extensively analyzed in vitro by means of protease protection assaying, it is unclear whether such assays allow elucidation of the insertion process faithfully, since the membrane-protected fragment, an index of membrane insertion, is a full-length polypeptide of F0 -c, which is the same as the protease-resistant conformation without membrane insertion. We found that the protease-resistant conformation could be discriminated from membrane-insertion by including octyl glucoside on protease digestion. By means of this system, we found that F0 -c insertion depends on MPIase, a glycolipozyme involved in membrane insertion, and is stimulated by YidC. In addition, we found that acidic phospholipids PG and CL transform F0 -c into a protease-resistant form, while MPIase prevents the acquisition of such a protease-resistant conformation.