Mitochondrial F(0) F(1) -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 F₁-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 IF_1,, 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.