Fig. 8.

Circadian control of critical cardiac processes. A: protein abundance differs in CCM vs. WT heart at different times of day or night, including rate-limiting enzymes important for vital metabolic pathways that provide substrate for the trichloroacetic acid (TCA) cycle. Identified proteins are circled. B: schematic diagram of the sarcomere, the functional unit of the cardiomyocyte. Contraction is achieved through complex interactions between the thin and thick filaments and the Z-disc. The thin filaments comprise proteins, including actin subunits, α-helix tropomyosin (Tm), and the troponin complex [troponin T (TnT), troponin I (TnT), and troponin C (TnC)]. Thick filaments are composed of a number of proteins, including myosin binding protein C (MyBP-C), and myosin heads consisting of myosin heavy chain (MHC) and myosin light chain (MLC) and magnesium-dependent ATPase (MgATPase). Z-discs consist of demsin, α-actinin, titin, and actin-capping protein (capZ) and other proteins to anchor filaments. Calcium binding to the troponin complex allows results in thin-filament conformational changes, permitting the myosin head of the thick filament to bind actin, leading to sarcomere contraction. When the myosin head is released, ATP is used by the Mg-dependent ATPase to hydrolyze ATP to ADP + Pi, and return the myosin head back to its starting conformation.