FIG 7.

Model for the assembly of TAAs. The three subunits of a TAA form an asymmetric trimer in the periplasm (step i). The partially folded trimer is then targeted to the OM, where the Bam complex catalyzes the membrane integration of the β barrel domain (step ii). A conformational change in the β barrel domain may be required to expose the passenger domains on the cell surface and to initiate translocation. Translocation proceeds through a hybrid channel comprised of open forms of the linked β barrel domain and the BamA β barrel (step iii). Translocation is driven at least in part by the folding of the passenger domains into a coiled-coil structure. Following the completion of the translocation reaction, the β barrel domain folds completely and dissociates from the Bam complex.