Ligand migration through the internal hydrophobic cavities in human neuroglobin
Ligand migration through the internal hydrophobic cavities in human neuroglobin
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DOI：
10.1073/pnas.0905433106
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发表时间：
2009-11-10
影响因子：
11.1
通讯作者：
Viappiani, Cristiano
中科院分区：
文献类型：
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作者：
Abbruzzetti, Stefania;Faggiano, Serena;Viappiani, Cristiano
脑红蛋白(NGB)是珠蛋白超家族中的一员，存在于脊椎动物的大脑中，在低氧条件下通过双加氧酶活性清除一氧化氮(NO)发挥神经保护作用。为了有效地进行这样的反应，并最大限度地减少胞浆中活性中间体的释放，共底物O-2和NO以及其他不稳定的反应中间体应该顺序地结合到蛋白质基质中的对接位置。我们通过分析在硅胶中观察到的NGB-CO络合物的纳秒闪光光解时观察到的双CO与血红素部分的结合动力学来表征这些位置的可及性。双链重新结合阶段表现出显著的复杂性，揭示了一个二级对接位置系统的存在，其中配体被存储了数百微秒。大多数动力学步骤对温度的依赖性很小，表明除了最慢的反应中间体外，配体可以很容易地通过空腔迁移，这可能反映了重塑空腔系统的结构构象变化。这种构象变化与His E7远端与血红素的结合无关，因为它对HE7L突变体持续存在。总体而言，数据与一个离散的对接位置系统的存在是一致的，可能作为假定的共底物和参与生理相关反应的其他活性物种的储存库。
Neuroglobin (Ngb), a member of the globin superfamily, was found in the brain of vertebrates and is suggested to play a neuroprotective function under hypoxic conditions by scavenging nitrogen monoxide ( NO) through a dioxygenase activity. In order for such a reaction to efficiently take place and to minimize the release of reactive intermediates in the cytosol, the cosubstrates O-2 and NO and other unstable reaction intermediates should bind sequentially to docking sites in the protein matrix. We have characterized the accessibility of these sites by analyzing the geminate CO rebinding kinetics to the heme moiety observed upon nanosecond flash photolysis of the Ngb-CO complex encapsulated in silica gels. The geminate rebinding phase showed a remarkable complexity, revealing the presence of a system of secondary docking sites where ligands are stored for hundreds of microseconds. Most kinetics steps display little temperature dependence, demonstrating that ligands can easily migrate through the cavities, except for the slowest reaction intermediate, possibly reflecting a structural conformational change reshaping the system of cavities. This conformational change is unrelated with distal His E7 binding to the heme, as it persists for the HE7L mutant. Overall, data are consistent with the presence of a discrete system of docking sites, possibly acting as reservoirs for the putative cosubstrates and for other reactive species involved in the physiologically relevant reaction.