"This study required a different way of thinking about image analysis. This is the first time we were able to structurally visualize the weak binding states of actin and myosin, not interpolated from crystal structures, and not interpolated from biophysical methods," said Dr. Hanein. "We were able to see structural changes in the myosin lever arm as well as in the actin interface as it propagates through the hydrolysis cycle."
Structural information from previous studies provided information about parts of this process, but until the present collaboration, visualizing Myosin V in its weakly bound state to actin had not been possible. The Hanein group captured snapshots of Myosin V at several points during a hydrolysis cycle. Their use of electron cryo-microscopy made it possible to visualize flexible structural domains, which tether the Myosin V, helping to keep the protein on its actin track through the weak binding phase of the processive movement.
The detailed molecular knowledge of how myosin interacts through the hydrolysis cycle with actin provides an exciting new research template onto which scientists can design new sets of experiments to further refine the myosin-actin binding region and to correlate it with loss or gain of function. The precise characterization of this myosin-actin interface is critical, evident by the way a single amino acid change in myosin leads to familial hypertrophic cardiomyopathy (FHC), an undetectable condition resulting in death by sudden cardiac arrest in otherwise healthy young adults.
Contributors to this work include: Niels Volkmann, Ph.D., assistant professor and first author on this publication, Dorit Hanein, Ph.D., associate professor, Hong-Jun Liu and Larnele Hazelwood from the Burnham Institute for Medical Research; and Kathleen M. Trybus, Ph.D., Susan Lowey, Ph.D., and Elena B. Kremen