title: The "second stalk" of Escherichia coli ATP synthase: structure of the isolated dimerization domain.
abstract: The b subunit of E. coli F(0)F(1)-ATPase links the peripheral F(1) subunits to the membrane-integral F(0) portion and functions as a "stator", preventing rotation of F(1). The b subunit is present as a dimer in ATP synthase, and residues 62-122 are required to mediate dimerization. To understand how the b subunit dimer is formed, we have studied the structure of the isolated dimerization domain, b(62-122). Analytical ultracentrifugation and solution small-angle X-ray scattering (SAXS) indicate that the b(62-122) dimer is extremely elongated, with a frictional ratio of 1.60, a maximal dimension of 95 A, and a radius of gyration of 27 A, values that are consistent with an alpha-helical coiled-coil structure. The crystal structure of b(62-122) has been solved and refined to 1.55 A. The protein crystallized as an isolated, monomeric alpha helix with a length of 90 A. Combining the crystal structure of monomeric b(62-122) with SAXS data from the dimer in solution, we have constructed a model for the b(62-122) dimer in which the two helices form a coiled coil with a right-handed superhelical twist. Analysis of b sequences from E. coli and other prokaryotes indicates conservation of an undecad repeat, which is characteristic of a right-handed coiled coil and consistent with our structural model. Mutation of residue Arg-83, which interrupts the undecad pattern, to alanine markedly stabilized the dimer, as expected for the proposed two-stranded, right-handed coiled-coil structure.
authors.affiliation: Department of Biochemistry, University of Western Ontario, London, ON N6A 5C1, Canada.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Del Rizzo
authors.forename: Yumin
authors.initials: Y
authors.lastname: Bi
authors.forename: Stanley D
authors.initials: SD
authors.lastname: Dunn
authors.forename: Brian H
authors.initials: BH
authors.lastname: Shilton
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry* / Q000235:genetics; D018360:Crystallography, X-Ray; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000235:genetics
chemical_list: D021122:Protein Subunits; D001120:Arginine; D006180:Proton-Translocating ATPases