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Water-coupled low-frequency modes of myoglobin and lysozyme observed by inelastic neutron scattering.

机译：非弹性中子散射观察到的肌红蛋白和溶菌酶的水耦合低频模式。

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摘要

Conformational changes of proteins often involve the relative motion of rigid structural domains. Normal mode analysis and molecular dynamics simulations of small globular proteins predict delocalized vibrations with frequencies below 20 cm(-1), which may be overdamped in solution due to solvent friction. In search of these modes, we have studied deuterium-exchanged myoglobin and lysozyme using inelastic neutron scattering in the low-frequency range at full and low hydration to modify the degree of damping. At room temperature, the hydrated samples exhibit a more pronounced quasielastic spectrum due to diffusive motions than the dehydrated samples. The analysis of the corresponding lineshapes suggests that water modifies mainly the amplitude, but not the characteristic time of fast protein motions. At low temperatures, in contrast, the dehydrated samples exhibit larger motional amplitudes than the hydrated ones. The excess scattering, culminating at 16 cm(-1), is suggested to reflect water-coupled librations of polar side chains that are depressed in the hydrated system by strong intermolecular hydrogen bonding. Both myoglobin and lysozyme exhibit ultra-low-frequency modes below 10 cm(-1) in the dry state, possibly related to the breathing modes predicted by harmonic analysis.
机译：蛋白质的构象变化通常涉及刚性结构域的相对运动。小球状蛋白的正常模式分析和分子动力学模拟预测频率低于20 cm（-1）的离域振动，由于溶剂的摩擦，其在溶液中可能被过度阻尼。在寻找这些模式时，我们研究了在低频和全水合条件下利用非弹性中子散射在氘交换的肌红蛋白和溶菌酶上改变阻尼度的方法。在室温下，由于扩散运动，水合样品表现出比脱水样品更明显的准弹性光谱。对相应线形的分析表明，水主要改变振幅，但不改变快速蛋白质运动的特征时间。相反，在低温下，脱水样品的运动幅度要大于脱水样品。建议在16 cm（-1）处达到最终的过量散射，以反映极性侧链的水耦合释放，该极性侧链在水合体系中由于强分子间氢键而被抑制。肌红蛋白和溶菌酶在干燥状态下均显示低于10 cm（-1）的超低频模式，这可能与谐波分析预测的呼吸模式有关。

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