Department of Chemistry, Duke University, Durham, NC 27708-0346, USA.
Metallomics. 2009;1(3):249-55. doi: 10.1039/b902860a.
Neisseria gonorrhoeae has the capacity to acquire iron from its human host by removing this essential nutrient from serum transferrin. The transferrin binding proteins, TbpA and TbpB constitute the outer membrane receptor complex responsible for binding transferrin, extracting the tightly bound iron from the host-derived molecule, and transporting iron into the periplasmic space of this Gram-negative bacterium. Once iron is transported across the outer membrane, ferric binding protein A (FbpA) moves the iron across the periplasmic space and initiates the process of transport into the bacterial cytosol. The results of the studies reported here define the multiple steps in the iron transport process in which TbpA and TbpB participate. Using the SUPREX technique for assessing the thermodynamic stability of protein-ligand complexes, we report herein the first direct measurement of periplasmic FbpA binding to the outer membrane protein TbpA. We also show that TbpA discriminates between apo- and holo-FbpA; i.e. the TbpA interaction with apo-FbpA is higher affinity than the TbpA interaction with holo-FbpA. Further, we demonstrate that both TbpA and TbpB individually can deferrate transferrin and ferrate FbpA without energy supplied from TonB resulting in sequestration by apo-FbpA.
淋病奈瑟菌能够从其人类宿主中获取铁，方法是从血清转铁蛋白中去除这种必需的营养物质。转铁蛋白结合蛋白 TbpA 和 TbpB 构成了负责结合转铁蛋白的外膜受体复合物，从宿主来源的分子中提取紧密结合的铁，并将铁运输到革兰氏阴性菌的周质空间。一旦铁穿过外膜被运输，三价铁结合蛋白 A（FbpA）将铁穿过周质空间，并启动将铁运输到细菌细胞质的过程。本报告中所述研究的结果定义了 TbpA 和 TbpB 参与的铁运输过程中的多个步骤。我们使用 SUPREX 技术评估蛋白-配体复合物的热力学稳定性，在此首次直接测量了周质 FbpA 与外膜蛋白 TbpA 的结合。我们还表明，TbpA 区分脱铁转铁蛋白和高铁 FbpA；即 TbpA 与脱铁 FbpA 的相互作用具有更高的亲和力，而 TbpA 与高铁 FbpA 的相互作用亲和力较低。此外，我们证明 TbpA 和 TbpB 单独可以使转铁蛋白和高铁 FbpA 去铁，而无需 TonB 提供能量，从而导致脱铁 FbpA 被螯合。
