Fig. 1.

Cartoon representation of the iron acquisition process of N. gonorrhoeae. Holo-transferrin is recognized and bound by TbpA/TbpB at the external surface of the outer membrane. Iron is released from transferrin and the apo-transferrin is released from the outer membrane receptor using TonB derived energy followed by transport of iron into the periplasm. In the periplasm apo-FbpA binds with TbpA and acquires the iron. FbpA then transports the iron across the periplasm and delivers it to the inner membrane receptors FbpB and FbpC which ultimately transport iron into the cytoplasm (the TbpA plug is not shown in the cartoon for clarity).