Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology , 2-4 Shirakata, Tokai, Ibaraki 319-1106, Japan.
Research Reactor Institute, Kyoto University , 2 Asashiro-Nishi, Kumatori, Osaka 590-0494, Japan.
J Phys Chem B. 2017 Aug 31;121(34):8069-8077. doi: 10.1021/acs.jpcb.7b05182. Epub 2017 Aug 17.
Hemoglobin, the vital O carrier in red blood cells, has long served as a classic example of an allosteric protein. Although high-resolution X-ray structural models are currently available for both the deoxy tense (T) and fully liganded relaxed (R) states of hemoglobin, much less is known about their dynamics, especially on the picosecond to subnanosecond time scales. Here, we investigate the picosecond dynamics of the deoxy and CO forms of human hemoglobin using quasielastic neutron scattering under near physiological conditions in order to extract the dynamics changes upon ligation. From the analysis of the global motions, we found that whereas the apparent diffusion coefficients of the deoxy form can be described by assuming translational and rotational diffusion of a rigid body, those of the CO form need to involve an additional contribution of internal large-scale motions. We also found that the local dynamics in the deoxy and CO forms are very similar in amplitude but are slightly lower in frequency in the former than in the latter. Our results reveal the presence of rapid large-scale motions in hemoglobin and further demonstrate that this internal mobility is governed allosterically by the ligation state of the heme group.
血红蛋白是红细胞中携带氧气的重要蛋白质，长期以来一直是变构蛋白的经典范例。尽管目前已经有脱氧紧张态（T）和完全配体松弛态（R）血红蛋白的高分辨率 X 射线结构模型，但对其动力学的了解要少得多，尤其是在皮秒到亚纳秒的时间尺度上。在这里，我们使用准弹性中子散射技术在接近生理条件下研究了脱氧和 CO 形式的人血红蛋白的皮秒动力学，以提取配体结合时的动力学变化。通过对整体运动的分析，我们发现，虽然脱氧形式的表观扩散系数可以通过假设刚性体的平移和旋转扩散来描述，但 CO 形式的那些则需要涉及内部大规模运动的额外贡献。我们还发现，脱氧和 CO 形式的局部动力学在幅度上非常相似，但前者的频率略低于后者。我们的结果揭示了血红蛋白中存在快速的大规模运动，并进一步证明这种内部流动性是由血红素基团的配体状态变构控制的。
