Changes in Magnesium Binding to Myosin with Oxidative Modification

Oxidative stress is an imbalance of detrimental oxidants and combating antioxidants. Muscle is a major target of oxidative stress due to generation of reactive oxygen species (ROS) through both physiological and pathological conditions. Decreased muscle force with aging is caused partially by defects in contractile proteins that produce muscle contraction, myosin and actin. Myosin binds to actin and adenosine triphosphate (ATP) which is hydrolyzed to ADP and inorganic phosphate to generate force. Actin is an allosteric activator of myosin’s activity, increasing the rate at which myosin hydrolyzes ATP. Oxidative damage has shown to be targeted to the actin/myosin binding interface and causes a decrease in myosin’s ATPase activity. Magnesium (Mg2+) is an inhibitor of myosin’s ATPase activity and interacts with myosin near its actin-binding site. This research investigates how oxidative modifications within myosin’s catalytic domain affect its functional interaction with actin and ability to bind magnesium. Dictyostelium discoideum (Dicty) myosin II was used as the model system to study myosin function. Oxidative modification in myosin was induced by treatment with hydrogen peroxide. Myosin’s ATPase activity under varying concentrations of free Mg2+ in the absence and presence of actin was measured using an NADHcoupled enzymatic assay detected by spectrophotometry at 340 nm. Our results show that varying [Mg2+] cause a change in the myosin’s functional interaction with actin. Understanding how oxidative modifications within myosin affect its interaction with binding partners give insight into the impact of oxidative stress on muscle function