Crystal structure of bovine mitochondrial factor B at 0.96-Å resolution

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Abstract
Coupling factor B (FB) is a mitochondrial inner membrane polypeptide that facilitates the energy-driven catalysis of ATP synthesis in animal mitochondria by blocking a proton leak across the membrane. Here, we report the crystal structure of the bovine mitochondrial FB mutant with Gly-3–Glu substitution determined at a resolution of 0.96 Å and that of the WT polypeptide at a resolution of 2.9 Å. The structure reveals an oblong, oval-shaped molecule with a unique globular N-terminal domain that is proposed to be the membrane anchor domain and the capping region to the C-terminal leucine-rich repeats domain. A short N-terminal α-helix, which extends away from the molecule9s body, is suggestive of functioning as an anchor for FB to the matrix side of the mitochondrial inner membrane. Identification of a bound Mg2+ ion reveals that FB is a metalloprotein. We also report the cocrystal structures of FB bound with phenylarsine oxide and Cd2+, two known inhibitors of the FB coupling activity.