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

Background & Purpose:  T1AM is a thyronamine derivative of thyroid hormone acting as a signalling molecule via non-genomic effectors and can reach intracellular targets. In light of the importance of F(0) F(1) -ATPsynthase as a target in drug development, T1AM interaction with the enzyme is demonstrated by its effects on the activity and a model of binding locations is depicted. Experimental Approach:  Kinetic analyses were performed on F(0) F(1) -ATPsynthase in sub-mitochondrial particles and soluble F(1) -ATPase. Activity assays and immunodetection of the inhibitor protein IF(1) were used and combined with molecular docking analyses. In situ respirometric analysis of T1AM effect was investigated on H9c2 cardiomyocytes. Key Results:  T1AM is a non-competitive inhibitor of F(0) F(1) -ATPsynthase whose binding is mutually exclusive with that of the inhibitors IF(1) and aurovertin B. Distinct T1AM binding sites are consistent with results from both kinetic and docking analyses: at low nanomolar concentrations, T1AM binds to a high affinity-region likely located within the IF(1) binding site, causing IF(1) release; at higher concentrations, T1AM binds to a low affinity-region likely located within the aurovertin binding cavity and inhibits enzyme activity. Low nanomolar concentrations of T1AM elicit in cardiomyocytes an increase in ADP-stimulated mitochondrial respiration indicative for an activation of F(0) F(1) -ATPsynthase consistent with displacement of endogenous IF(1, ) thereby reinforcing the in vitro results. Conclusions & Implications:  The T1AM effects upon F(0) F(1) -ATPsynthase are twofold: IF(1) displacement and enzyme inhibition. By targeting F(0) F(1) -ATPsynthase within mitochondria T1AM might affect cell bioenergetics with a positive effect on mitochondrial energy production at low endogenous concentration. T1AM putative binding locations overlapping with IF(1) and aurovertin binding sites are depicted.