title: Molecular disruption of the power stroke in the ATP-binding cassette transport protein MsbA.
abstract: ATP-binding cassette transporters affect drug pharmacokinetics and are associated with inherited human diseases and impaired chemotherapeutic treatment of cancers and microbial infections. Current alternating access models for ATP-binding cassette exporter activity suggest that ATP binding at the two cytosolic nucleotide-binding domains provides a power stroke for the conformational switch of the two membrane domains from the inward-facing conformation to the outward-facing conformation. In outward-facing crystal structures of the bacterial homodimeric ATP-binding cassette transporters MsbA from gram-negative bacteria and Sav1866 from Staphylococcus aureus, two transmembrane helices (3 and 4) in the membrane domains have their cytoplasmic extensions in close proximity, forming a tetrahelix bundle interface. In biochemical experiments on MsbA from Escherichia coli, we show for the first time that a robust network of inter-monomer interactions in the tetrahelix bundle is crucial for the transmission of nucleotide-dependent conformational changes to the extracellular side of the membrane domains. Our observations are the first to suggest that modulation of tetrahelix bundle interactions in ATP-binding cassette exporters might offer a potent strategy to alter their transport activity.
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom.
authors.forename: Rupak
authors.initials: R
authors.lastname: Doshi
authors.forename: Anam
authors.initials: A
authors.lastname: Ali
authors.forename: Wilma
authors.initials: W
authors.lastname: Shi
authors.forename: Elizabeth V
authors.initials: EV
authors.lastname: Freeman
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Fagg
authors.forename: Hendrik W
authors.initials: HW
authors.lastname: van Veen
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D001692:Biological Transport; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; C079726:MsbA protein, Bacteria; D000255:Adenosine Triphosphate