Sec/SRP Requirements and Energetics of Membrane Insertion of Subunits a, b, and c of the Escherichia coli F1F0 ATP Synthase.

Previously, the role of YidC in the membrane protein biogenesis of the F0 sector of the Escherichia coli F1F0 ATP synthase was investigated. Whereas subunits a and c of the F1F0 ATP synthase were strictly dependent on YidC for membrane insertion, subunit b required YidC for efficient insertion (Yi, L., Jiang, F., Chen, M., Cain, B., Bolhuis, A., and Dalbey, R. E. (2003) Biochemistry 42, 10537–10544). In this paper, we investigated other protein components and energetics that are required in the membrane protein assembly of the F0 sector subunits. We show here that the Sec translocase and the signal recognition particle (SRP) pathway are required for membrane insertion of subunits a and b. In contrast, subunit c required neither the Sec machinery nor the SRP pathway for insertion. While the proton motive force was not required for insertion of subunits b and c, it was required for translocation of the negatively charged periplasmic NH2-terminal tail of subunit a, whereas periplasmic loop 2 of subunit a could insert in a proton motive force-independent manner. Taken together, the in vivo data suggest that subunits a and b are inserted by the Sec/SRP pathway with the help of YidC, and subunit c is integrated into the membrane by the novel YidC pathway. [ABSTRACT FROM AUTHOR]