The Staphylococcus aureus IsdH Receptor Forms a Dynamic Complex with Human Hemoglobin that Triggers Heme Release via Two Distinct Hot Spots
The Staphylococcus aureus IsdH Receptor Forms a Dynamic Complex with Human Hemoglobin that Triggers Heme Release via Two Distinct Hot Spots
复制标题
DOI：
10.1016/j.jmb.2019.12.023
复制
发表时间：
2020-02-14
影响因子：
5.6
通讯作者：
Clubb, Robert T.
中科院分区：
文献类型：
--
作者：
Ellis-Guardiola, Ken;Clayton, Joseph;Clubb, Robert T.
铁是细菌病原体在感染期间主动获得的必需营养素。临床上重要的金黄色葡萄球菌通过使用密切相关的IsdB和IsdH表面受体从血红蛋白（Hb）中提取血红素来获得铁。在IsdH中，提取由保守的三结构域单元介导，该三结构域单元包含通过螺旋接头连接的第二（N2）和第三（N3）NEAT结构域，称为IsdH（N2 N3）。利用IsdH（N2 N3）：Hb复合物的晶体结构，我们已经探讨了血红素捕获的机制，使用NMR，停流转移动力学测量，和分子动力学（MD）模拟。220 kDa的IsdH（N2 N3）：Hb复合物的NMR研究表明，它是动态的，与持续的域间运动，使连接器和N3域的受体瞬时从事血红蛋白，以消除其血红素。丙氨酸诱变分析表明，两个受体亚位点定位类似于20埃分开触发血红素释放接触血红蛋白的F-螺旋。这些亚位点位于N3和接头结构域内，并且似乎在稳定血红素转移过渡态中发挥不同的作用。接头结构域接触主要起使Hb-血红素相互作用不稳定的作用，从而降低Δ H双匕首，而来自N3亚位点的接触起类似的不稳定作用，但也形成血红素从Hb移动到受体的桥梁。有趣的是，MD模拟表明，在瞬时形成的接口，F-螺旋和受体桥都在运动中，动态采样构象，适合血红素转移。因此，IsdH通过在溶液中快速形成的柔性低亲和力界面触发血红素从Hb释放。(C)2019由Elsevier Ltd.出版
Iron is an essential nutrient that is actively acquired by bacterial pathogens during infections. Clinically important Staphylococcus aureus obtains iron by extracting heme from hemoglobin (Hb) using the closely related IsdB and IsdH surface receptors. In IsdH, extraction is mediated by a conserved tridomain unit that contains its second (N2) and third (N3) NEAT domains joined by a helical linker, called IsdH(N2N3). Leveraging the crystal structure of the IsdH(N2N3):Hb complex, we have probed the mechanism of heme capture using NMR, stopped-flow transfer kinetics measurements, and molecular dynamics (MD) simulations. NMR studies of the 220 kDa IsdH(N2N3):Hb complex reveal that it is dynamic, with persistent interdomain motions enabling the linker and N3 domains in the receptor to transiently engage Hb to remove its heme. An alanine mutagenesis analysis reveals that two receptor subsites positioned similar to 20 angstrom apart trigger heme release by contacting Hb's F-helix. These subsites are located within the N3 and linker domains and appear to play distinct roles in stabilizing the heme transfer transition state. Linker domain contacts primarily function to destabilize Hb-heme interactions, thereby lowering Delta H double dagger, while contacts from the N3 subsite play a similar destabilizing role, but also form a bridge through which heme moves from Hb to the receptor. Interestingly, MD simulations suggest that within the transiently forming interface, both the F-helix and receptor bridge are in motion, dynamically sampling conformations that are suitable for heme transfer. Thus, IsdH triggers heme release from Hb via a flexible, low-affinity interface that forms fleetingly in solution. (C) 2019 Published by Elsevier Ltd.