A SUBUNIT INTERACTION IN CHLOROPLAST ATP SYNTHASE DETERMINED BY GENETIC COMPLEMENTATION BETWEEN CHLOROPLAST AND BACTERIAL ATP SYNTHASE GENES

F1F0-ATP synthases utilize protein conformational changes induced by a transmembrane proton gradient to synthesize ATP. The allosteric coope rativity of these multisubunit enzymes presumably requires numerous pr otein-protein interactions within the enzyme complex. To correlate kno wn in vitro changes in subunit structure with in vivo allosteric inter actions, we introduced the beta subunit of spinach chloroplast couplin g factor 1 ATP into a bacterial F-1 ATP synthase. A cloned atpB gene, encoding the complete chloroplast beta subunit, complemented a chromos omal deletion of the cognate uncD gene in Escherichia coil and was inc orporated into a functional hybrid F-1 ATP synthase. The cysteine resi due at position 63 in chloroplast beta is known to be located at the i nterface between alpha and beta subunits and to be conformationally co upled, in vitro, to the nucleotide binding site >40 Angstrom away. Enl arging the side chain of chloroplast coupling factor 1 beta residue 63 from Cys to Trp blocked ATP synthesis in vivo without significantly i mpairing ATPase activity or ADP binding in vitro. The in vivo coupling of nucleotide binding at catalytic sites to transmembrane proton move ment may thus involve an interaction, via conformational changes, betw een the amino-terminal domains of the alpha and beta subunits.