Figure 6.

Models of possible TatB-precursor interactions. (A) The gray bar represents the lipid bilayer. Each TatC molecule is depicted by six stippled transmembrane helices. Four TatB monomers are shown (diagonally hatched cylinders) with their transmembrane helices contacting one TatC protomer each (the front TatC subunit has been omitted for clarity) and with their cytosolic amphipathic helices encapsulating a folded Tat precursor (black ellipse). The twin-arginine signal sequence (++) is represented by a black line. Its contacts to TatB and TatC are speculative. The tetrameric nature of the TatBC complex is based on previous findings (Lee et al., 2006), but the model would easily accommodate higher order oligomeric structures. (B) Two Tat precursor molecules simultaneously binding to TatB as suggested by recent data (Tarry et al., 2009b; Ma and Cline, 2010).