Desolvation of the substrate-binding protein TauA dictates ligand specificity for the alkanesulfonate ABC importer TauABC

Biochem J. 2019 Dec 12;476(23):3649-3660. doi: 10.1042/BCJ20190779.


Under limiting sulfur availability, bacteria can assimilate sulfur from alkanesulfonates. Bacteria utilize ATP-binding cassette (ABC) transporters to internalise them for further processing to release sulfur. In gram-negative bacteria the TauABC and SsuABC ensure internalization, although, these two systems have common substrates, the former has been characterized as a taurine specific system. TauA and SsuA are substrate-binding proteins (SBPs) that bind and bring the alkanesulfonates to the ABC importer for transport. Here, we have determined the crystal structure of TauA and have characterized its thermodynamic binding parameters by isothermal titration calorimetry in complex with taurine and different alkanesulfonates. Our structures revealed that the coordination of the alkanesulfonates is conserved, with the exception of Asp205 that is absent from SsuA, but the thermodynamic parameters revealed a very high enthalpic penalty cost for binding of the other alkanesulfonates relative to taurine. Our molecular dynamic simulations indicated that the different levels of hydration of the binding site contributed to the selectivity for taurine over the other alkanesulfonates. Such selectivity mechanism is very likely to be employed by other SBPs of ABC transporters.

Keywords: ABC transport proteins; crystallography; molecular dynamics; thermodynamics.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / chemistry*
  • ATP-Binding Cassette Transporters / metabolism*
  • Alkanesulfonates / metabolism*
  • Base Sequence
  • Binding Sites
  • Carrier Proteins / metabolism*
  • Crystallization
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / metabolism*
  • Hydrogen Bonding
  • Ligands
  • Molecular Dynamics Simulation
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism
  • Protein Binding
  • Protein Domains
  • Protein Transport
  • Substrate Specificity
  • Sulfur / metabolism
  • Taurine / metabolism
  • Thermodynamics


  • ATP-Binding Cassette Transporters
  • Alkanesulfonates
  • Carrier Proteins
  • Escherichia coli Proteins
  • Ligands
  • Mutant Proteins
  • SsuA protein, E coli
  • TauA protein, E coli
  • Taurine
  • Sulfur