The interactions of molecular tracks and motors result in movements in cells. Fundamental to our understanding of the way in which motility is accomplished in cells is a detailed description not only of the atomic structures of the complexes involved, but also the way in which the activity of these complexes is regulated in response to the needs of the cell. The long term goals of the work described in this application are to understand in structural terms, the way in which myosin motors are regulated. Three types of myosin-based regulation will be investigated: (I) Regulation mediated by light chain phosphorylation will be investigated by examining a number of smooth muscle myosin constructs. (ii) Regulation by light chain dissociation will be examined in brush border myosin l and myosin V. (iii) Regulation by heavy chain phosphorylation will be investigated in Acanthamoeba and Dictyostelium myosin ls. The methods to be used include cryoelectron microscopy, helical image analysis and modeling using the x-ray structures of the myosin head and regulatory domain. The experiments have been designed to visualize actomyosin conformations which are the basis of the regulatory mechanism. Atomic models of the regulated and activated states will be built from the EM and X-ray data. The results should provide detailed insights into the structural basis for regulation in myosin involved in uterine contractions, blood pressure maintenance and intestinal peristalsis (smooth muscle myosin), and in intracellular trafficking and endocytosis (myosin ls and Vs). Some exploratory experiments on dynein are planned.
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