A distinct mechanism for the ABC transporter BtuCD-BtuF revealed by the dynamics of complex formation

Nat Struct Mol Biol. 2010 Mar;17(3):332-8. doi: 10.1038/nsmb.1770. Epub 2010 Feb 21.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / metabolism*
  • Bacterial Proteins / metabolism
  • Biological Transport / physiology
  • Chromatography, Gel
  • Escherichia coli Proteins / metabolism*
  • Kinetics
  • Periplasmic Binding Proteins / metabolism*
  • Protein Binding
  • Thermodynamics
  • Vitamin B 12 / metabolism

Substances

  • ATP-Binding Cassette Transporters
  • Bacterial Proteins
  • BtuC peptide, E coli
  • BtuD peptide, E coli
  • Escherichia coli Proteins
  • Periplasmic Binding Proteins
  • btuF protein, E coli
  • Vitamin B 12