Characterization of the relationship between ADP- and ε-induced inhibition in cyanobacterial F1-ATPase

Abstract

The ATPase activity of chloroplast and bacterial F1-ATPase is strongly inhibited by both the endogenous inhibitor ε and tightly bound ADP. Although the physiological significance of these inhibitory mechanisms is not very well known for the membrane-bound F0F1, these are very likely to be important in avoiding the futile ATP hydrolysis reaction and ensuring efficient ATP synthesis in vivo. In a previous study using the α3β3γ complex of F1 obtained from the thermophilic cyanobacteria, Thermosynechococcus elongatus BP-1, we succeeded in determining the discrete stop position, ∼ 80° forward from the pause position for ATP binding, caused by ε-induced inhibition (ε-inhibition) during γ rotation (Konno, H., Murakami-Fuse, T., Fujii, F., Koyama, F., Ueoka-Nakanishi, H., Pack, C. G., Kinjo, M., and Hisabori, T. (2006) EMBO J. 25, 4596-4604). Because γ in ADP-inhibited F1 also pauses at the same position, ADP-induced inhibition (ADP-inhibition) was assumed to be linked to ε-inhibition. However, ADP-inhibition and ε-inhibition should be independent phenomena from each other because the ATPase core complex, α3β 3γ, also lapses into the ADP-inhibition state. By way of thorough biophysical and biochemical analyses, we determined that the ε subunit inhibition mechanism does not directly correlate with ADP-inhibition. We suggest here that the cyanobacterial ATP synthase ε subunit carries out an important regulatory role in acting as an independent "braking system" for the physiologically unfavorable ATP hydrolysis reaction. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.