Molecular Energetics of Protein Motors

蛋白质马达的能量方面通过各种方法进行了研究，包括微波介电光谱和肌球蛋白马达水解ATP的量热法，沿沿着微管运动的单个驱动蛋白分子的直接观察，单个肌球蛋白分子的单个ATP周转的成像，肌球蛋白分子与互补结合的核苷酸的小角X射线衍射，肌肉的X射线衍射，肌球蛋白与不同核苷酸复合的X射线晶体学，肌动蛋白分子的扩散增强荧光共振能量转移，蛋白质马达的溶剂化自由能模拟，驱动蛋白沿沿着微管滑动的涨落分析，马达蛋白的快速冷冻深蚀刻复制品图像的立体照相术，以及马达蛋白的定点诱变。这些研究表明：1.肌球蛋白表面疏水性的改变在肌球蛋白ATP水解过程中的熵-熵补偿效应中起着至关重要的作用; 2.蛋白马达可以调节化学变化（ATP水解）和机械输出之间的耦合模式，这取决于施加在它们身上的负载。因此，ATP水解酶的能量以某种方式储存在运动蛋白中，在每个动力冲程周期中部分地使用。3.肌动蛋白分子表面的两个负电位位点中，一个位于肌球蛋白结合位点附近，另一个位于鬼笔环肽结合位点附近，没有受到明显影响; 4.由单噪声轨迹得到的滑移细丝位移涨落的有效扩散系数是建立力化学耦合模型的有用参数。

Energetic aspects of protein motors were investigated by various methods including microwave-dielectric spectroscopy and calorimetry of myosin motors hydrolyzind ATP,direct observation of simgle kinesin molecules moving along microtubules, imaging of individual ATP turnovers by single myosin molecules, small-angle X-ray diffeaction of myosin molecules with diffrrent bound nucleotides, X-ray diffraction of muscle, X-ray crystallography of myosin complexed with different nucleotides, diffusion-enhanced fluorescence resonance energy transfer of actin molecules, simulation of solvation free-energy of protein motors, fluctuation analysis of kinesin sliding along microtubule, stereo-photogramtry of quick-freeze deep-etch replica images of motor proteins, and site-directed mutagenesis of motor proteins. These studies indicate that :1.the myosin surface hydrophobicity change plays a crucial role in the enthalpy-entropy compensation effectc observed in the steps of myosin ATP hydrolysis ;2.protein motors can modulate the mode of coupling between chemical change (ATP hydrolysis) and mechanical output depending on load imposed on them. Thus, the energy of ATP hydrolys is somehow stored in the motor protein, which is used fractionally at each power stroke cycle. This would mean that the protein motor operate with energy conversion efficiency as high as more than 50% using the energy input comparable to or marginally above the thermal energy ;3.Of two negative potential sites of actin molecule surface, one around the myosin binding site while the other site around the phalloidin binding site is not significantly affected ;4.an effective diffusion coefficient from displacement fluctuations of a sliding filament obtained from its single noisy trajectory is a useful parameters for constructing the models for mechanochemical coupling.