University of Minnesota Ph.D. dissertation. 2020. Major: Biochemistry, Molecular Bio, and Biophysics. Advisor: David Thomas. 1 computer file (PDF); 112 pages.Healthy muscle function hinges upon balanced contraction and relaxation cycling of muscle proteins. The main proteins involved are myosin and actin, making them desirable therapeutic targets for modulating muscle dysfunctions. In relaxation, the two heads of myosin have been shown to form an auto-associated state, that is hypothesized to be an auto-inhibited state with extremely slow ATP turnover, termed the super-relaxed state (SRX). Numerous efforts are underway to understand the biophysical properties of the SRX and its physiological roles in skeletal, cardiac, and smooth muscle. SRX is involved in resting skeletal muscle thermogenesis and in cardiac muscle contractility, with profound implications for health issues such as obesity, aging, and heart disease. Part of my thesis research focuses on the relationship of SRX to aging in skeletal muscle, as measured by quantitative epifluorescence microscopy, to fill in the knowledge gap between basic biophysics and muscle physiology. This is the first time that myosin SRX is directly studied through the physiological lens of aging. The long-term goal is to establish the role of SRX in age-related attenuation of muscle function, especially in humans, and to use these insights to design therapeutic approaches. Progress on this topic is presented and discussed in Chapter 2 (correlation of SRX with aging in mouse muscle) and Chapter 3 (the first SRX measurements in human muscle, correlated with fiber type). Some of this work has been published previously1, and that article has been adapted, with permissions, to fit the format of this dissertation. Actin, the main binding partner of myosin, is the focus of Chapter 4. I established biochemical and biophysical assays that can be used to complement the fluorescence resonance energy transfer (FRET)-based technology our lab has pioneered for drug discovery targeting actin. These assays allow us to further identify potential therapeutic compounds that are specific to skeletal or cardiac muscle. Overall, my studies lay the groundwork for applying biophysical techniques, such as optical spectroscopy, to translational science, to elucidate the molecular basis of disease and to set the stage for development of new treatments
