title: A distinct mechanism for the ABC transporter BtuCD-BtuF revealed by the dynamics of complex formation.
abstract: ATP-binding cassette (ABC) transporters are integral membrane proteins that translocate a diverse array of substrates across cell membranes. We present here the dynamics of complex formation of three structurally characterized ABC transporters-the BtuCD vitamin B(12) importer and MetNI d/l-methionine importer from Escherichia coli and the Hi1470/1 metal-chelate importer from Haemophilus influenzae-in complex with their cognate binding proteins. Similarly to other ABC importers, MetNI interacts with its binding protein with low affinity (K(d) approximately 10(-4) M). In contrast, BtuCD-BtuF and Hi1470/1-Hi1472 form stable, high-affinity complexes (K(d) approximately 10(-13) and 10(-9) M, respectively). In BtuCD-BtuF, vitamin B(12) accelerates the complex dissociation rate approximately 10(7)-fold, with ATP having an additional destabilizing effect. The findings presented here highlight substantial mechanistic differences between BtuCD-BtuF, and likely Hi1470/1-Hi1472, and the better-characterized maltose and related ABC transport systems, indicating that there is considerable mechanistic diversity within this large protein super-family.
authors.affiliation: Division of Chemistry and Chemical Engineering, Pasadena, California, USA.
authors.forename: Oded
authors.initials: O
authors.lastname: Lewinson
authors.forename: Allen T
authors.initials: AT
authors.lastname: Lee
authors.forename: Kaspar P
authors.initials: KP
authors.lastname: Locher
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Rees
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D002850:Chromatography, Gel; D029968:Escherichia coli Proteins / Q000378:metabolism*; D007700:Kinetics; D033902:Periplasmic Binding Proteins / Q000378:metabolism*; D011485:Protein Binding; D013816:Thermodynamics; D014805:Vitamin B 12 / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; C050021:BtuC peptide, E coli; C050022:BtuD peptide, E coli; D029968:Escherichia coli Proteins; D033902:Periplasmic Binding Proteins; C446048:btuF protein, E coli; D014805:Vitamin B 12