Crystallographic structure of the turbine C-ring from spinach chloroplast F-ATP synthase

In eukaryotic and prokaryotic cells, F-ATP synthases provide energy through the synthesis of ATP. The chloroplast F-ATP synthase (CF₁ F _O-ATP synthase) of plants is integrated into the thylakoid membrane via its F_O-domain subunits a, b, b′ and c. Subunit c with a stoichiometry of 14 and subunit a form the gate for H⁺ -pumping, enabling the coupling of electrochemical energy with ATP synthesis in the F ₁ sector. Here we report the crystallization and structure determination of the c14-ring of subunit c of the CF₁F _O-ATP synthase from spinach chloroplasts. The crystals belonged to space group C2, with unit-cell parameters a = 144.420, b = 99.295, c = 123.51 Å, and β = 104.34° and diffracted to 4.5 Å resolution. Each c-ring contains 14 monomers in the asymmetric unit. The length of the c-ring is 60.32 Å, with an outer ring diameter 52.30 Å and an inner ring width of 40 Å.