Fig. 6.

Model for structural organization and activity of the HTL. (A) The SecYEG translocon can associate with SecDF–YajC–YidC (Left) to promote protein transport in a SecA-dependent fashion. This translocation reaction can be stimulated by the presence of a PMF and the anionic phospholipid CL. SecYEG dimers (Center), arranged in a back-to-back orientation via SecE–E interactions, are capable of mediating the same reaction, but the effect of the PMF is less. Membrane protein integration (Right) may preferentially use the SecYEG–SecDF–YajC–YidC setup (the holo-translocon) for insertion of newly synthesized transmembrane helices directly into the lipid bilayer. (B) Top view of proposed interactions for the YEG dimer and holo-translocon. Black bars represent subunit cross-links.