Direct Effects of Toxic Divalent Cations on Contractile Proteins with Implications for the Heart: Unraveling Mechanisms of Dysfunction

The binding of calcium and magnesium ions to proteins is crucial for regulating heart contraction. However, other divalent cations, including xenobiotics, can accumulate in the myocardium and enter cardiomyocytes, where they can bind to proteins. In this article, we summarized the impact of these cations on myosin ATPase activity and EF-hand proteins, with special attention given to toxic cations. Optimal binding to EF-hand proteins occurs at an ionic radius close to that of Mg(2+) and Ca(2+). In skeletal Troponin C, Cd(2+), Sr(2+), Pb(2+), Mn(2+), Co(2+), Ni(2+), Ba(2+), Mg(2+), Zn(2+), and trivalent lanthanides can substitute for Ca(2+). As myosin ATPase is not a specific MgATPase, Ca(2+), Fe(2+), Mn(2+), Ni(2+), and Sr(2+) could support myosin ATPase activity. On the other hand, Zn(2+) and Cu(2) significantly inhibit ATPase activity. The affinity to various divalent cations depends on certain proteins or their isoforms and can alter with amino acid substitution and post-translational modification. Cardiac EF-hand proteins and the myosin ATP-binding pocket are potential molecular targets for toxic cations, which could significantly alter the mechanical characteristics of the heart muscle at the molecular level.