Regulation of the biogenesis of chloroplast ATP synthase

Chloroplast ATP synthase belongs to the F-type ATP synthases. It is localized in the thylakoid membrane and consists of nine subunits with a stoichiometry of alpha(3)beta(3)gamma(1)epsilon(1)delta(1)alpha(1)b(1)b'(1)c(14). Since its subunits are encoded by both nuclear and chloroplast genomes, its biogenesis requires an intricate coordination of gene expression between these two genetic systems as well as a tight regulation of assembly by various chloroplast protein chaperones. Isolation of mutants defective in the biogenesis of chloroplast ATP synthase and detailed characterization of the corresponding genes revealed the existence of several pentatricopeptide repeat (PPR) proteins that are required for proper expression of chloroplast atp genes at various post-transcriptional steps including RNA splicing, RNA editing, RNA stabilization as well as protein translation. As other F-type ATP synthases, assembly of the chloroplast ATP synthase occurs in a stepwise manner through the formation of several transient intermediates. Several chaperones facilitate the assembly of chloroplast ATP synthase by interacting with specific subunits at different stages. In particular, structural studies of some assembly factors have provided many new insights into the assembly of the chloroplast ATP synthase at the molecular level. Because the structure and the assembly pathway of the F-type ATP synthase are highly conserved among most species, some of the assembly mechanisms of chloroplast ATP synthase are likely to be valid for other ATP synthases.