Structural study on the architecture of the bacterial ATP synthase F o motor

Abstract

We purified the Fo complex from the Ilyobacter tartaricus Na+- translocating F1Fo-ATP synthase and performed a biochemical and structural study. Laser-induced liquid bead ion desorption MS analysis demonstrates that all three subunits of the isolated Fo complex were present and in native stoichiometry (ab 2c11). Cryoelectron microscopy of 2D crystals yielded a projection map at a resolution of 7.0 Å showing electron densities from the c11 rotor ring and up to seven adjacent helices. A bundle of four helices belongs to the stator a-subunit and is in contact with c11. A fifth helix adjacent to the four-helix bundle interacts very closely with a c-subunit helix, which slightly shifts its position toward the ring center. Atomic force microscopy confirms the presence of the Fostator, and a height profile reveals that it protrudes less from the membrane than c 11. The data limit the dimensions of the subunit a/c-ring interface: Three helices from the stator region are in contact with three c11 helices. The location and distances of the stator helices impose spatial restrictions on the bacterial Fo complex.