Caronna Chiara, Natali Francesca, Cupane Antonio
INFM OGG & CRS-SOFT, 6 rue Jules Horowitz, BP 156-38042 Grenoble Cedex 9, France.
Biophys Chem. 2005 Aug 1;116(3):219-25. doi: 10.1016/j.bpc.2005.02.004.
In this work we investigate the dynamic properties of hemoglobin in glycerolD(8)/D(2)O solution using incoherent elastic (ENS) and quasi-elastic (QENS) neutron scattering. Taking advantage of complementary energy resolutions of backscattering spectrometers at ILL (Grenoble), we explore motions in a large space-time window, up to 1 ns and 14 A; moreover, in order to cover the harmonic and anharmonic protein dynamics regimes, the elastic experiments have been performed over the wide temperature interval of 20-300 K. To study the dependence of the measured dynamics upon the protein quaternary structure, both deoxyhemoglobin (in T quaternary conformation) and carbonmonoxyhemoglobin (in R quaternary conformation) have been investigated. From the ENS data the mean square displacements of the non-exchangeable hydrogen atoms of the protein and their temperature dependence are obtained. In agreement with previous results on hydrated powders, a dynamical transition at about 220 K is detected. The results show interesting differences between the two hemoglobin quaternary conformations, the T-state protein appearing more rigid and performing faster motions than the R-state one; however, these differences involve motions occurring in the nanosecond time scale and are not detected when only faster atomic motions in the time scale up to 100 ps are investigated. The QENS results put in evidence a relevant Lorentzian quasi-elastic contribution. Analysis of the dependence of the Elastic Incoherent Structure Factor (EISF) and of the Lorentzian halfwidth upon the momentum transfer suggests that the above quasi-elastic contribution arises from the diffusion inside a confined space, values of confinement radius and local diffusion coefficient being compatible with motions of hydrogen atoms of the amino acid side chains. When averaged over the whole range of momentum transfer the QENS data put in evidence differences between deoxy and carbonmonoxy hemoglobin and confirm the quaternary structure dependence of the protein dynamics in the nanosecond time scale.
在这项工作中，我们使用非相干弹性（ENS）和准弹性（QENS）中子散射研究了血红蛋白在甘油 - D(8)/D(2)O溶液中的动力学性质。利用位于法国格勒诺布尔劳厄 - 郎之万研究所（ILL）的背散射光谱仪的互补能量分辨率，我们探索了在高达1纳秒和14埃的大时空窗口内的运动；此外，为了涵盖蛋白质的谐波和非谐波动力学机制，弹性实验在20 - 300 K的宽温度区间内进行。为了研究测量的动力学对蛋白质四级结构的依赖性，我们对脱氧血红蛋白（处于T四级构象）和碳氧血红蛋白（处于R四级构象）都进行了研究。从ENS数据中获得了蛋白质不可交换氢原子的平均平方位移及其温度依赖性。与先前关于水合粉末的结果一致，检测到在约220 K处有一个动力学转变。结果显示了两种血红蛋白四级构象之间有趣的差异，T态蛋白质比R态蛋白质显得更刚性且运动更快；然而，这些差异涉及纳秒时间尺度内发生的运动，并且当仅研究高达100皮秒时间尺度内的更快原子运动时未被检测到。QENS结果表明存在一个相关的洛伦兹准弹性贡献。对弹性非相干结构因子（EISF）和洛伦兹半高宽对动量转移的依赖性分析表明，上述准弹性贡献源于受限空间内的扩散，受限半径和局部扩散系数的值与氨基酸侧链氢原子的运动相匹配。当在整个动量转移范围内进行平均时，QENS数据显示了脱氧血红蛋白和碳氧血红蛋白之间的差异，并证实了蛋白质动力学在纳秒时间尺度上对四级结构的依赖性。
