title: Exploring conformational equilibria of a heterodimeric ABC transporter.
abstract: ABC exporters pump substrates across the membrane by coupling ATP-driven movements of nucleotide binding domains (NBDs) to the transmembrane domains (TMDs), which switch between inward- and outward-facing (IF, OF) orientations. DEER measurements on the heterodimeric ABC exporter TM287/288 fromThermotoga maritima, which contains a non-canonical ATP binding site, revealed that in the presence of nucleotides the transporter exists in an IF/OF equilibrium. While ATP binding was sufficient to partially populate the OF state, nucleotide trapping in the pre- or post-hydrolytic state was required for a pronounced conformational shift. At physiologically high temperatures and in the absence of nucleotides, the NBDs disengage asymmetrically while the conformation of the TMDs remains unchanged. Nucleotide binding at the degenerate ATP site prevents complete NBD separation, a molecular feature differentiating heterodimeric from homodimeric ABC exporters. Our data suggest hydrolysis-independent closure of the NBD dimer, which is further stabilized as the consensus site nucleotide is committed to hydrolysis.
authors.affiliation: Faculty of Chemistry and Biochemistry, Ruhr-Universität Bochum, Bochum, Germany.|Department of Physics, Freie Universität Berlin, Berlin, Germany.
authors.forename: M Hadi
authors.initials: MH
authors.lastname: Timachi
authors.affiliation: Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland.
authors.forename: Cedric Aj
authors.initials: CA
authors.lastname: Hutter
authors.affiliation: Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Hohl
authors.affiliation: Faculty of Chemistry and Biochemistry, Ruhr-Universität Bochum, Bochum, Germany.|Department of Physics, Freie Universität Berlin, Berlin, Germany.
authors.forename: Tufa
authors.initials: T
authors.lastname: Assafa
authors.affiliation: Laboratory of Physical Chemistry, ETH Zurich, Zurich, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Böhm
authors.affiliation: Department of Biochemistry, University of Zurich, Zurich, Switzerland.
authors.forename: Anshumali
authors.initials: A
authors.lastname: Mittal
authors.affiliation: Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland.
authors.forename: Markus A
authors.initials: MA
authors.lastname: Seeger
authors.affiliation: Faculty of Chemistry and Biochemistry, Ruhr-Universität Bochum, Bochum, Germany.|Department of Physics, Freie Universität Berlin, Berlin, Germany.
authors.forename: Enrica
authors.initials: E
authors.lastname: Bordignon
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D020124:Thermotoga maritima / Q000201:enzymology*
chemical_list: D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate
keywords: ABC transporter; DEER; E. coli; biophysics; electron paramagnetic resonance; structural biology