Insights into the subunit interactions of the chloroplast ATP synthase

Subunit interactions of the chloroplast F0F1-ATP synthase were studied using the yeast two-hybrid system. The coding sequences of all the nine subunits of spinach chloroplast ATP synthase were cloned in two-hybrid vectors. The vectors were transformed into the yeast strains HF7c and SFY526 by various pairwise combinations, and the protein interactions were analyzed by measuring the yeast growth on minimal SD medium without serine, lucine and histidine. Interactions of gamma subunit with wild type or two truncated mutants of epsilon sununit, eDeltaN21 and cDeltaC45, which lose their abilities to inhibit the ATP hydrolysis, were also detected by in vitro and in vivo binding assay. The present results are largely accordant to the common structure model of F0F1-ATP synthase. Different from that in the E. coli F0F1-ATP synthase, the delta subunit of chloroplast ATP synthase could interact with beta, gamma, epsilon and all the CF0 subunits in the two-hybrid system. These results suggested that though the chloroplast ATP synthase shares the similar structure and composition of subunits with the enzyme from E. coli, it may be different in the subunit interactions and conformational change during catalysis between these two sources of ATP synthase. Based on the present results and our knowledge of structure model of E. coli ATP synthase, a deduced structure model of chloroplast ATP synthase was proposed.