Fig. 8.

Model of the regulation of TatA pore formation by TatBC and substrate. (A) The inactive monomeric form of TatA accommodates the depth of the membrane by tilting the short TMH, increasing the angle between the TMH and the APH, and deeply inserting the APH into the membrane. (B) Interactions with TatBC/substrate complex force an orientation of the TatA TMH roughly parallel to the membrane normally favoring TatA polymerization. The N terminus is pulled into the membrane thinning and distorting the bilayer in the pore and sensitizing the membrane to disruption. The TatA APH serves as a platform for the substrate that is tethered to the TatBC complex by a signal peptide. In the drawing the TatA oligomeric ring is represented by two opposing subunits. (C) Pulling of substrate protein into the membrane forces TatA subunits apart and ruptures the membrane.