Structure of Escherichia coli BamB and its interaction with POTRA domains of BamA

In Escherichia coli, the BAM complex is essential for the assembly and insertion of outer membrane proteins (OMPs). The BAM complex is comprised of an integral β-barrel outer membrane protein BamA and four accessory lipoproteins BamB, BamC, BamD and BamE. Here, the crystal structure of BamB is reported. The crystal of BamB diffracted to 2.0 Å with one monomer in the asymmetric unit and the structure is composed of eight-bladed β-propeller motifs. Pull-down and Western blotting assays indicate that BamB interacts directly with the POTRA 1–3 domain of BamA and the C-­terminal region of the POTRA 1–3 domain plays an important role in the interaction, while the POTRA 1–2 domain is not required for the interaction.