β Subunit THR-159 And GLU-195 of the Rhodospirillum Rubrum ATP Synthase Are Essential for Divalent Cation Dependent Catalysis

Abstract

The crystal structures of rat mitochondrial MF₁ at 3.6 Å [1] and bovine MF₁ at 2.8 Å [2] confirm the alternating arrangement of the six large α and β subunits in a closed hexamer. In the high-resolution structure the three catalytic β subunits have different bound nucleotides and display different conformational states. This structure contains also about half of the γ subunit amino-acid residues, composed mainly of the N and C terminal helices, that are embedded within the internal cavity of the α₃β₃ hexamer. The asymmetric structure imposed on this hexamer by interaction of the γ-subunit with the three different β-subunits [2], supports the binding change mechanism [3]. This mechanism suggests that ATP synthesis involves transitions between different but interacting catalytic sites via rotation of the ? subunit relative to an α₃β₃ subassembly. Full elucidation of the as yet unresolved mechanism of ATP synthesis will depend on identification of all amino-acid residues on the β and γ subunits that participate in catalysis.