Monomeric structure and native folding öfsubunit c 01- h+transporting fif₀ atpase

The H- transporting FiF0ATP synthase complex of oxidative phosphorylation is organized in two sectors, an FI ATPase moiety lying extrinsic to the membrane and a membrane traversing F() sector which promotes l\+ transport. Subunit c is one of three subunits found in the F0 moiety o!" the complex. It is a small protein of 79 residues, found in 9-12 copies per Fq, and it is known to directly catalyze H+ transport. Subunit c is known to fold in the membrane as a hairpin of two hydrophobia ahelices with a more polar loop region exposed to the Fj binding side of the membrane. Aspol centered in the second transmembrane helix is known to protonate and deprotonate during H transport. Suhunii c has been purified in monomeric form in a single phase solvent mixture of chloroform-rnethanol-water (4:4:1 ) made 50 mM in NaCl. By a number of criteria, the protein folds in this solvent mixture as it is expected to fold in r he membrane. A high resolution structure of the protein has now been completed by a series of triple resonance NMR methods. The structure will be considered and compared to the expected properties for the protein in native F0. The two helices pack close to each other with an interdigitalion of Hydrophobie side chains into spaces created by (Jly and Ala in the opposite helix. Asp61 in Helix-2 lies within a Hydrophobie cavity in close contact to Ala24 in helix-1, as predicted from genetic studies. [Supported by PUS Grant GM-23105|.