The structure of the chloroplast F-1-ATPase at 3.2 angstrom 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 structur e of the bovine mitochondrial enzyme. The crystallized complex contains fou r 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 mitocho ndrial and thermophilic subunits. However, in the crystal structure of the chloroplast enzyme, all alpha- and beta -subunits adopt a closed conformati on and appear to contain no bound adenine nucleotides. The superimposed cry stallographic symmetry in the space group R32 impaired an exact tracing of the gamma- and epsilon -subunits in the complex. However, clear electron de nsity was present at the core of the alpha (3),beta (3)-subcomplex, which p robably represents the C-terminal domain of the gamma -subunit, The structu re of the spinach chloroplast F-1 has a potential binding site for the phyt otoxin, tentoxin, at the cup-interface near beta Asp(83) and an insertion f rom beta Gly(56)-Asn(60) in the N-terminal beta -barrel domain probably inc reases the thermal stability of the complex. The structure probably represe nts an inactive latent state of the ATPase, which is unique to chloroplast and cyanobacterial enzymes.