The structure of the chloroplast F1-ATPase at 3.2 Å resolution

The structure of the F-1-ATPase from spinach chloroplasts was determined to 3.2 A resolution by molecular replacement based on the homologous structure of the bovine mitochondrial enzyme. The crystallized complex contains four different subunits in a stoichiometry of alpha (3)beta (3)gamma epsilon. Subunit delta was removed before crystallization to improve the diffraction of the crystals. The overall structure of the noncatalytic alpha -subunits and the catalytic beta -subunits is highly similar to those of the mitochondrial and thermophilic subunits. However, in the crystal structure of the chloroplast enzyme, all alpha- and beta -subunits adopt a closed conformation and appear to contain no bound adenine nucleotides. The superimposed crystallographic symmetry in the space group R32 impaired an exact tracing of the gamma- and epsilon -subunits in the complex. However, clear electron density was present at the core of the alpha (3),beta (3)-subcomplex, which probably represents the C-terminal domain of the gamma -subunit, The structure of the spinach chloroplast F-1 has a potential binding site for the phytotoxin, tentoxin, at the cup-interface near beta Asp(83) and an insertion from beta Gly(56)-Asn(60) in the N-terminal beta -barrel domain probably increases the thermal stability of the complex. The structure probably represents an inactive latent state of the ATPase, which is unique to chloroplast and cyanobacterial enzymes.