The ATP synthase of Escherichia coli: structure and function of F-0 subunits

In this review we discuss recent work from our laboratory concerning the st ructure and/or function of the F-0 subunits of the proton-translocating ATP synthase of Escherichia coli. For the topology of subunit tr a brief discu ssion gives (i) a detailed picture of the C-terminal two-thirds of the prot ein with four transmembrane helices and the C terminus exposed to the cytop lasm and (ii) an evaluation of the controversial results obtained for the l ocalization of the N-terminal region of subunit a including its consequence s on the number of transmembrane helices. The structure of membrane-bound s ubunit b has been determined by circular dichroism spectroscopy to be at le ast 75% alpha-helical, For this purpose a method was developed, which allow s the determination of the structure composition of membrane proteins in pr otroliposomes. Subunit b, was purified to homogeneity by preparative SDS ge l electrophoresis, precipitated with acetone, and redissolved in cholate-co ntaining buffer, thereby retaining its native conformation as shown by func tional coreconstitution with an ne subcomplex. Monoclonal antibodies, which have their epitopes located within the hydrophilic loop region of subunit c, and the F-1 part are bound simultaneously to the F-0 complex without an effect on the function of F-0, indicating that not all c subunits are invol ved in F-1 interaction. Consequences on the coupling mechanism between ATP synthesis/hydrolysis and proton translocation are discussed. (C) 2000 Elsev ier Science B.V. All rights reserved.