Structural features of the γ subunit of the Escherichia coli F(1) ATPase revealed by a 4.4-Å resolution map obtained by x-ray crystallography

The F(1) part of the F(1)F(O) ATP synthase from Escherichia coli has been crystallized and its structure determined to 4.4-Å resolution by using molecular replacement based on the structure of the beef-heart mitochondrial enzyme. The bacterial F(1) consists of five subunits with stoichiometry α(3), β(3), γ, δ, and ɛ. δ was removed before crystallization. In agreement with the structure of the beef-heart mitochondrial enzyme, although not that from rat liver, the present study suggests that the α and β subunits are arranged in a hexagonal barrel but depart from exact 3-fold symmetry. In the structures of both beef heart and rat-liver mitochondrial F(1), less than half of the structure of the γ subunit was seen because of presumed disorder in the crystals. The present electron-density map includes a number of rod-shaped features which appear to correspond to additional α-helical regions within the γ subunit. These suggest that the γ subunit traverses the full length of the stalk that links the F(1) and F(O) parts and makes significant contacts with the c subunit ring of F(O).