Effects of Mutations and Ligands on the Thermostability of the l-Arginine/Agmatine Antiporter AdiC and Deduced Insights into Ligand-Binding of Human l-Type Amino Acid Transporters

Int J Mol Sci. 2018 Mar 20;19(3):918. doi: 10.3390/ijms19030918.


The l-arginine/agmatine transporter AdiC is a prokaryotic member of the SLC7 family, which enables pathogenic enterobacteria to survive the extremely acidic gastric environment. Wild-type AdiC from Escherichia coli, as well as its previously reported point mutants N22A and S26A, were overexpressed homologously and purified to homogeneity. A size-exclusion chromatography-based thermostability assay was used to determine the melting temperatures (Tms) of the purified AdiC variants in the absence and presence of the selected ligands l-arginine (Arg), agmatine, l-arginine methyl ester, and l-arginine amide. The resulting Tms indicated stabilization of AdiC variants upon ligand binding, in which Tms and ligand binding affinities correlated positively. Considering results from this and previous studies, we revisited the role of AdiC residue S26 in Arg binding and proposed interactions of the α-carboxylate group of Arg exclusively with amide groups of the AdiC backbone. In the context of substrate binding in the human SLC7 family member l-type amino acid transporter-1 (LAT1; SLC7A5), an analogous role of S66 in LAT1 to S26 in AdiC is discussed based on homology modeling and amino acid sequence analysis. Finally, we propose a binding mechanism for l-amino acid substrates to LATs from the SLC7 family.

Keywords: ">l-arginine/agmatine transporter; ">l-type amino acid transporter; AdiC; LAT1; acid resistance; cancer metabolism; enterobacteria; melting temperature; thermostability.

MeSH terms

  • Amino Acid Transport Systems / chemistry*
  • Amino Acid Transport Systems / genetics
  • Amino Acid Transport Systems / metabolism
  • Antiporters / chemistry*
  • Antiporters / genetics
  • Antiporters / metabolism
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism
  • Hot Temperature
  • Humans
  • Large Neutral Amino Acid-Transporter 1 / chemistry
  • Large Neutral Amino Acid-Transporter 1 / metabolism*
  • Ligands
  • Molecular Dynamics Simulation*
  • Mutation*
  • Protein Binding
  • Protein Stability*
  • Sequence Homology


  • AdiC protein, E coli
  • Amino Acid Transport Systems
  • Antiporters
  • Escherichia coli Proteins
  • Large Neutral Amino Acid-Transporter 1
  • Ligands