Mitochondrial F0F1-ATP synthase is a molecular target of 3-iodothyronamine, an endogenous metabolite of thyroid hormone

BACKGROUND AND PURPOSE 3-iodothyronamine (T1AM) is a metabolite of thyroid hormone acting as a signalling molecule via non-genomic effectors and can reach intracellular targets. Because of the importance of mitochondrial F0F1-ATP synthase as a drug target, here we evaluated interactions of T1AM with this enzyme. EXPERIMENTAL APPROACH Kinetic analyses were performed on F0F1-ATP synthase in sub-mitochondrial particles and soluble F-1-ATPase. Activity assays and immunodetection of the inhibitor protein IF1 were used and combined with molecular docking analyses. Effects of T1AM on H9c2 cardiomyocytes were measured by in situ respirometric analysis. KEY RESULTS T1AM was a non-competitive inhibitor of F0F1-ATP synthase whose binding was mutually exclusive with that of the inhibitors IF1 and aurovertin B. Both kinetic and docking analyses were consistent with two different binding sites for T1AM. At low nanomolar concentrations, T1AM bound to a high-affinity region most likely located within the IF1 binding site, causing IF1 release. At higher concentrations, T1AM bound to a low affinity-region probably located within the aurovertin binding cavity and inhibited enzyme activity. Low nanomolar concentrations of T1AM increased ADP-stimulated mitochondrial respiration in cardiomyocytes, indicating activation of F0F1-ATP synthase consistent with displacement of endogenous IF1,, reinforcing the in vitro results. CONCLUSIONS AND IMPLICATIONS Effects of T1AM on F0F1-ATP synthase were twofold: IF1 displacement and enzyme inhibition. By targeting F0F1-ATP synthase within mitochondria, T1AM might affect cell bioenergetics with a positive effect on mitochondrial energy production at low, endogenous, concentrations. T1AM putative binding locations overlapping with IF1 and aurovertin binding sites are described.