Studies on muscle contraction Mechanism based on molecular structure of mutant motor proteins

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Our goal is to understand the molecular mechanism of motor proteins on the basis of atomic structure of proteins.First we developed new techniques for electron microscopy. Using one of new techniques we developed, that is, the site-directed heavy atom labelling electron microscopy (SHALEM), we decided the position of the 5^<th> amino acid of myosin only by electron microscopy. Also, we reconstructed three-dimensional structure of muscle during isometric contraction.Second, we detected the structural change of myosin during ATP hyrdrolysis by electron microscopy, small angle X-ray scattering, and crystallography using X-ray diffraction. This is the first observation of detection of myosin structural change during ATP hydrolysis.Third, we observed the structural change of thin filaments in the addition of Ca ions by cryo-electron microscopy.Last, we found the myosin-actin interaction sites on the subdomain-1 of actin using protein engineering techniques. Also we found the motor domain of myosin. This part is essential for sliding movement of actin and production of force. Furthermore, we use protein engineering to produce the mutant actins, which activate myosin ATPase in a highly cooperative manner. We found that the replacement of only 3 amino acid residues cause the high cooperativity in Ca^<2+>-induced activation of ATPase. This region is also one of the binding sites of tropomyosin in the presence of Ca.