title: The c13 ring from a thermoalkaliphilic ATP synthase reveals an extended diameter due to a special structural region.
abstract: We have structurally characterized the c-ring from the thermoalkaliphilic Bacillus sp. strain TA2.A1 F(1)F(o)-ATP synthase. Atomic force microscopy imaging and cryo-electron microscopy analyses confirm previous mass spectrometric data indicating that this c-ring contains 13 c-subunits. The cryo-electron microscopy map obtained from two-dimensional crystals shows less closely packed helices in the inner ring compared to those of Na(+)-binding c(11) rings. The inner ring of alpha-helices in c(11) rings harbors a conserved GxGxGxGxG motif, with glycines located at the interface between c-subunits, which is responsible for the close packing of these helices. This glycine motif is altered in the c(13) ring of Bacillus sp. strain TA2.A1 to AxGxSxGxS, leading to a change in c-c subunit contacts and thereby enlarging the c-ring diameter to host a greater number of c-subunits. An altered glycine motif is a typical feature of c-subunit sequences in alkaliphilic Bacillus species. We propose that enlarged c-rings in proton-dependent F-ATP synthases may represent an adaptation to facilitate ATP synthesis at low overall proton-motive force, as occurs in bacteria that grow at alkaline pH.
authors.affiliation: Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, Frankfurt am Main, Germany.
authors.forename: Doreen
authors.initials: D
authors.lastname: Matthies
authors.forename: Laura
authors.initials: L
authors.lastname: Preiss
authors.forename: Adriana L
authors.initials: AL
authors.lastname: Klyszejko
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Muller
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Cook
authors.forename: Janet
authors.initials: J
authors.lastname: Vonck
authors.forename: Thomas
authors.initials: T
authors.lastname: Meier