Functional diversity of tandem substrate-binding domains in ABC transporters from pathogenic bacteria

Structure. 2013 Oct 8;21(10):1879-88. doi: 10.1016/j.str.2013.07.020. Epub 2013 Aug 29.


The ATP-binding cassette (ABC) transporter GlnPQ is an essential uptake system for amino acids in gram-positive pathogens and related nonpathogenic bacteria. The transporter has tandem substrate-binding domains (SBDs) fused to each transmembrane domain, giving rise to four SBDs per functional transporter complex. We have determined the crystal structures and ligand-binding properties of the SBDs of GlnPQ from Enterococcus faecalis, Streptococcus pneumoniae, and Lactococcus lactis. The tandem SBDs differ in substrate specificity and affinity, allowing cells to efficiently accumulate different amino acids via a single ABC transporter. The combined structural, functional, and thermodynamic analysis revealed the roles of individual residues in determining the substrate affinity. We succeeded in converting a low-affinity SBD into a high-affinity receptor and vice versa. Our data indicate that a small number of residues that reside in the binding pocket constitute the major affinity determinants of the SBDs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / chemistry*
  • ATP-Binding Cassette Transporters / genetics
  • Amino Acid Substitution
  • Amino Acid Transport Systems, Basic / chemistry*
  • Amino Acid Transport Systems, Basic / genetics
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Binding Sites
  • Crystallography, X-Ray
  • Enterococcus faecalis*
  • Glutamine / chemistry
  • Hydrogen Bonding
  • Hydrophobic and Hydrophilic Interactions
  • Lactococcus lactis*
  • Ligands
  • Models, Molecular
  • Mutagenesis, Site-Directed
  • Protein Binding
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Streptococcus pneumoniae*
  • Substrate Specificity


  • ATP-Binding Cassette Transporters
  • Amino Acid Transport Systems, Basic
  • Bacterial Proteins
  • Ligands
  • Glutamine