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内容記述 |
The myosin-actin system is one of the typical systems related to intracellular movements. Using the hydrolyzing energy of ATP to ADP, the "motor" protein, myosin, generates force to move along the F-actin “track”. During the ATP hydrolysis cycle, the myosin head, containing the motor domain and the lever arm, undergoes various intermediate states. However, the force-generation mechanism is still elusive. Because of flexibility in the myosin head, the orientation of the lever arm relative to the motor domain fluctuates significantly. If and how these fluctuations are related to the force-generation mechanism need to be elucidated. Here, by quasielastic neutron scattering (QENS), fluctuations of the myosin head in various states were investigated. We prepared myosin subfragment 1 (S1), containing the myosin head, from chicken by papain-digestion, in the apo state, the ATP state (using a non-hydrolyzable ATP-analogue, AMPPNP), the ADP-Pi states (mimicked by complexes with ADP-AlF4 and ADP-BeFn), and the ADP state. The QENS measurements were carried out using the spectrometer BL02 (DNA) at the J-PARC. Analysis of the QENS spectra obtained showed that the lever arm motions become significant by ATP-binding, and disappear during hydrolysis of ATP to ADP, indicating that the molecule becomes rigid in this state (the actual state will be specified at the presentation.). These results imply that rigidifying the myosin head and binding to actin generates force during ATP hydrolysis. The changes in flexibility of the myosin head are thus incorporated in the force-generation mechanism during the ATP hydrolysis cycle. |
