Fig. 4.

Components involved in the biogenesis of transmembrane β-barrels in Gram-negative bacteria. Cartoon representation of the crystal structures of the major players involved in OMP biogenesis in the bacterial outer membrane. These include (i) the SecYEG translocon (PDB ID 5CH4) in the inner membrane (green, purple, pink), (ii) periplasmic proteins Skp (PDB ID 1U2M; gold) and SurA (PDB ID 1M5Y; dark blue), (iii) the BAM complex (PDB ID 5AYW) in the outer membrane (BamA, green; and the four lipoproteins: BamB, red; BamC, purple; BamD, gold; BamE, blue). BamA is further made up of five N-terminal extra-membrane POTRA domains located in the periplasm, and the transmembrane region is formed by the C-terminal 16-stranded β-barrel domain. The folded OMP (shown here is the folded OmpX barrel; PDB ID 1QJ8) is in dark grey. DegP is omitted from this schematic. All structures were obtained from the PDB and were rendered using PyMOL. The path traveled by the unfolded OMP (nascent protein; uOMP) is indicated as dotted lines with arrowheads.