14-3-3 protein is a regulator of the mitochondrial and chloroplast ATP synthase

Mitochondrial and chloroplast ATP synthases are key enzymes in plant metabo lism, providing cells with ATP, the universal energy currency. ATP synthase s use a transmembrane electrochemical proton gradient to drive synthesis of ATP. The enzyme complexes function as miniature rotary engines, ensuring e nergy coupling with very high efficiency. Although our understanding of the structure and functioning of the synthase has made enormous progress in re cent years, our understanding of regulatory mechanisms is still rather prel iminary, Here we report a role for 14-3-3 proteins in the regulation of ATP synthases, These 14-3-3 proteins are highly conserved phosphoserine/phosph othreonine-binding proteins that regulate a wide range of enzymes in plants , animals, and yeast. Recently, the presence of 14-3-3 proteins in chloropl asts was illustrated, and we show here that plant mitochondria harbor 14-3- 3s within the inner mitochondrial-membrane compartment. There, the 14-3-3 p roteins were found to be associated with the ATP synthases, in a phosphoryl ation-dependent manner, through direct interaction with the F-1 beta -subun it. The activity of the ATP synthases in both organelles is drastically red uced by recombinant 14-3-3. The rapid reduction in chloroplast ATPase activ ity during dark adaptation was prevented by a phosphopeptide containing the 14-3-3 interaction motif, demonstrating a role for endogenous 14-3-3 in th e down-regulation of the CFoF1 activity. Mle conclude that regulation of th e ATP synthases by 14-3-3 represents a mechanism for plant adaptation to en vironmental changes such as light/dark transitions, anoxia in roots, and fl uctuations in nutrient supply.