Figure 1 - The subunit of F₁F₀ ATP synthase, Sun, is an agonist of Methuselah.

Sun (red circle) could get to the extracellular space by secretion from the mitochondrial ATP synthase, or it could be found on the cell surface. The peptide antagonists identified by Ja et al. compete with Sun for binding to Mth. Both flies expressing a peptide antagonist and sun mutant flies have enhanced longevity.