Assembly and Function of the Chloroplast ATP Synthase

The F0F1 type H+-translocating ATPase (‘ATP synthase’) is a central enzyme of bacterial, mitochondrial and chloroplast energy transducing membranes. The function of the chloroplast enzyme complex (CF0CF1) is the formation of ATP from ADP and phosphate at the expense of energy derived from a transmembrane electrochemical proton potential difference which is built up by photosynthetic electron transport (photophosphorylation). Recent results on the molecular genetics, structure and mechanism of the chloroplast enzyme, supplemented with data from its bacterial and mitochondrial counterparts, convey a more complete and precise image of this enzyme complex. The biosynthesis of CF0CF1 which requires the interplay between the nuclear and plastid genome, depends on a variety of regulatory factors. The nuclear genes are controlled by light and by plastid derived factors, the expression of the chloroplast-synthesized subunits is regulated at the transcriptional and the translational level. The crystal structure of the mitochondrial F1 supplied important structural information concerning the catalytic sites of the enzyme, and mutagenesis and crosslinking studies with the E. coli enzyme helped to localize important domains of interaction of the F1 part with F0. It is now well-established that catalysis and energy coupling involve movements of the ATPase structure, and regulation of CF0CF1 also involves conformational changes. The structural basis and the molecular mechanisms of those motions are subjects of intensive research. C. reinhardtii has become a model organism for the investigation of CF0CF1 mechanisms and biogenesis, due to its easy cultivation, the advances in molecular characterization of the ATP synthase genes, the possibilities for site-directed mutagenesis in the plastid as well as in the nuclear genome and improved methods for biochemical analysis. These studies will be especially helpful for the understanding of mechanistic and regulatory aspects that are specific for chloroplast ATP synthesis. This chapter reviews the state of knowledge about photosynthetic ATP synthases with special reference to work performed with C. reinhardtii.