Structure of the subunit c oligomer in the F1Fo ATP synthase: model derived from solution structure of the monomer and cross-linking in the native enzyme.
The structure of the subunit c oligomer of the H+-transporting ATP synthase of Escherichia coli has been modeled by molecular dynamics and energy minimization calculations from the solution structure of monomeric subunit c and 21 intersubunit distance constraints derived from cross-linking of subunits. Subunit c folds in a hairpin-like structure with two transmembrane helices. In the c12 oligomer model, the subunits pack to form a compact hollow cylinder with an outer diameter of 55-60 A and an inner space with a minimal diameter of 11-12 A. Phospholipids are presumed to pack in the inner space in the native membrane. The transmembrane helices pack in two concentric rings with helix 1 inside and helix 2 outside. The calculations strongly favor this structure versus a model with helix 2 inside and helix 1 outside. Asp-61, the H+-transporting residue, packs toward the center of the four transmembrane helices of two interacting subunits. From this position at the front face of one subunit, the Asp-61 carboxylate lies proximal to side chains of Ala-24, Ile-28, and Ala-62, projecting from the back face of a second subunit. These interactions were predicted from previous mutational analyses. The packing supports the suggestion that a c-c dimer is the functional unit. The positioning of the Asp-61 carboxyl in the center of the interacting transmembrane helices, rather than at the periphery of the cylinder, has important implications regarding possible mechanisms of H+-transport-driven rotation of the c oligomer during ATP synthesis.
Department of Biomolecular Chemistry, University of Wisconsin Medical School, Madison, WI 53706, USA.
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Dmitriev
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Jones
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Fillingame
D000409:Alanine; D001224:Aspartic Acid; D003432:Cross-Linking Reagents; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology*; D007532:Isoleucine; D046911:Macromolecular Substances; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010743:Phospholipids / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary; D006180:Proton-Translocating ATPases / Q000737:chemistry*; D012996:Solutions; D055672:Static Electricity
D003432:Cross-Linking Reagents; D046911:Macromolecular Substances; D010743:Phospholipids; D012996:Solutions; D007532:Isoleucine; D001224:Aspartic Acid; D006180:Proton-Translocating ATPases; D000409:Alanine