SUBUNIT ORGANIZATION AND STRUCTURE IN THE F-0 SECTOR OF ESCHERICHIA-COLI F1F0 ATP SYNTHASE

In this review, we summarize recent work from our laboratory which est ablishes the topology and nearest neighbor organization of subunits in the F-0 sector of the H+ transporting ATP synthase of Escherichia col i. The E. coli F-0 sector is composed of three subunits in an a(1)b(2) c(12) stoichiometric ratio. Crosslinking experiments with genetically introduced Cys establish a ring-like organization of the 12 c subunits with subunits a and b lying to the outside of the ring. The results a re interpreted using an atomic resolution structural model of monomeri c subunit c in a chloroform-methanol-water (4:4:1, v/v/v) solution, de rived by heteronuclear NMR (M.E. Girvin, F. Abildgaard, V. Rastogi, J. Markley, R.H. Fillingame, in press). The crosslinking results validat e many predictions of the structural model and confirm a front-to-back -type packing of two subunit c into a functional dimer, as was first p redicted from genetic studies. Aspartyl-61, the proton translocating r esidue, lies at the center of the four transmembrane helices of the fu nctional dimer, rather than at the periphery of the subunit c ring. Su bunit a is shown to fold with five transmembrane helices, and a functi onally important interaction of transmembrane helix-4 with transmembra ne helix-2 of subunit c is established. The single transmembrane helic es of the two subunit b dimerize in the membrane. The structure of the transmembrane segment of subunit b is predicted from the NMR structur e of the monomeric peptide. (C) 1998 Elsevier Science B.V.