Molecular Energetics of Protein Motors

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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.