FIGURE 7.

Model for capture of Tf by TbpB. Iron-loaded (holo) Tf is captured by TbpB with the N-terminal anchor region in a fully extended conformation. This places TbpB beyond the lipo oligosaccharide side chains and the polysaccharide capsule. The binding of Tf by the N-terminal lobe of TbpB displaces the anchor peptide from its interaction with the C-terminal lobe and results in conformational changes in the anchor peptide that bring the TbpB-Tf complex closer to the surface of the outer membrane and capable of interacting with “activated” TbpA (bound to TonB). Tf released by TbpB is readily captured by the activated TbpA so that the iron removal and transport process can proceed, resulting in release of apoTf.