title: Asymmetric states of vitamin B₁₂ transporter BtuCD are not discriminated by its cognate substrate binding protein BtuF.
abstract: BtuCD is an ABC transporter catalyzing the uptake of vitamin B₁₂ across the Escherichia coli inner membrane. A previously reported X-ray structure of BtuCD in complex with the periplasmic vitamin B₁₂-binding protein BtuF revealed asymmetry of the transmembrane BtuC subunits. The functional relevance of this asymmetry has remained uncertain. Here we report the X-ray structure of a catalytically impaired BtuCD mutant in complex with BtuF, where the BtuC subunits adopt a distinct asymmetric conformation. The structure suggests that BtuF does not discriminate between, or impose, asymmetric conformations of BtuCD. It also explains the conformational disorder observed in BtuCDF crystals.
authors.affiliation: Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, Switzerland.
authors.forename: Vladimir M
authors.initials: VM
authors.lastname: Korkhov
authors.forename: Samantha A
authors.initials: SA
authors.lastname: Mireku
authors.forename: Rikki N
authors.initials: RN
authors.lastname: Hvorup
authors.forename: Kaspar P
authors.initials: KP
authors.lastname: Locher
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D019943:Amino Acid Substitution; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D033902:Periplasmic Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; C050021:BtuC peptide, E coli; C050022:BtuD peptide, E coli; D029968:Escherichia coli Proteins; D050505:Mutant Proteins; D033902:Periplasmic Binding Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; C446048:btuF protein, E coli; D000255:Adenosine Triphosphate