Figure 4.

The BAM complex. (A), Structure of the entire BamABCDE complex determined by cryo EM (PDB 5LJO). The ß1 and ß16 strands in the BamA ß-barrel are colored red in an open conformation. The external loops on BamA are also colored, with loop-4 and loop-6 indicated. (B), Depiction of a possible folding mechanism in which the ß1-ß16 lateral gate in the BamA ß-barrel opens and acts as a template for binding the first C-terminal ß-strand of the precursor OMP. Repeated further opening and hairpin insertions lead to folding and finally budding out of the complete ß-barrel (see text for further details).