Structure of a thermophilic F-1-ATPase inhibited by an epsilon-subunit: deeper insight into the epsilon-inhibition mechanism

F-1-ATPase (F-1) is the catalytic sector in FoF1-ATP synthase that is responsible for ATP production in living cells. In catalysis, its three catalytic -subunits undergo nucleotide occupancy-dependent and concerted open-close conformational changes that are accompanied by rotation of the -subunit. Bacterial and chloroplast F-1 are inhibited by their own epsilon-subunit. In the epsilon-inhibited Escherichiacoli F-1 structure, the epsilon-subunit stabilizes the overall conformation (half-closed, closed, open) of the -subunits by inserting its C-terminal helix into the (33) cavity. The structure of epsilon-inhibited thermophilic F-1 is similar to that of E.coli F-1, showing a similar conformation of the epsilon-subunit, but the thermophilic epsilon-subunit stabilizes another unique overall conformation (open, closed, open) of the -subunits. The epsilon-C-terminal helix2 and hook are conserved between the two structures in interactions with target residues and in their positions. Rest of the epsilon-C-terminal domains are in quite different conformations and positions, and have different modes of interaction with targets. This region is thought to serve epsilon-inhibition differently. For inhibition, the epsilon-subunit contacts the second catches of some of the - and -subunits, the N- and C-terminal helices, and some of the Rossmann fold segments. Those contacts, as a whole, lead to positioning of those - and - second catches in epsilon-inhibition-specific positions, and prevent rotation of the -subunit. Some of the structural features are observed even in IF1 inhibition in mitochondrial F-1. DatabaseStructural data are available in the Worldwide Protein Data Bank database under the accession number