Tripartite ATP-Independent Periplasmic (Trap) Transporters Use an Arginine-Mediated Selectivity Filter for High Affinity Substrate Binding.

摘要: Tripartite ATP-independent periplasmic (TRAP) transporters are secondary that have evolved an obligate dependence on a substrate-binding protein (SBP) to confer unidirectional transport. Different members of the DctP family TRAP SBPs binding sites recognize diverse range organic acid ligands but appear only share common electrostatic interaction between conserved arginine and carboxylate group in ligand. We investigated significance this using sialic acid-specific SBP, SiaP, from Haemophilus influenzae virulence-related SiaPQM transporter. Using vitro, vivo, structural methods applied we demonstrate coordination acidic ligand moiety by (Arg-147) is essential for function transporter as high affinity scavenging system. However, at substrate concentrations, can absence Arg-147 suggesting bi-molecular not involved further stages transport cycle. As well being required binding, also strong selectivity filter carboxylate-containing substrates engineering SBP non-carboxylate-containing substrate, sialylamide, through water-mediated interactions. Together, these data provide biochemical support predominantly substrates.