2-Deoxy-Atp Enhances Multiple Kinetic Parameters To Improve Cardiac Function

Hypertrophic cardiomyopathy (HCM) is a form of genetic heart disease often caused by point mutations in sarcomeric proteins. As the underlying mechanisms of genetic HCM continue to be unraveled, developing novel ways to modulate the actomyosin contractile apparatus is of growing interest and importance. The nucleotide analog 2-deoxyadenosine triphosphate (dATP) has recently garnered interest as potentially having therapeutic benefit for treatment of systolic and/or diastolic heart failure. dATP has been previously reported to enhance cardiac contractility, increase +dP/dt, and improve diastolic relaxation parameters in transgenic mice with elevated levels of dATP in the heart (Korte, 2011). When compared to ATP, dATP has been reported to increase steady state ATPase activity, and sliding velocities in the in vitro motility assay up to 50% (Regnier et al 2000). To better understand potential therapeutic benefits of dATP on actomyosin, we characterize the mechanism of action for dATP using bovine cardiac myosin subfragments S1 and HMM in a variety of steady-state, transient, and single-molecule experiments. We report a 40% increase in unloaded in vitro motility sliding velocities, as well as increased ATPase activity, ADP release rates, and actin-binding affinities with dATP compared to ATP. The combination of transient kinetic rates and equilibrium constants of the actomyosin ATPase cycle, as well as basal myosin parameters, implicate ADP release as the primary contributor to the differences observed between the two nucleotides. We propose a model by which enhancing both cardiac contraction and relaxation kinetics can improve cardiac function and potentially serve as a therapeutic for genetic heart disease.