Tripartite ATP-independent Periplasmic (TRAP) Transporters use an arginine-mediated selectivity filter for high affinity substrate binding

Background: Haemophilus influenzae requires a substrate-binding protein (SBP)-dependent TRAP transporter to acquire sialic acid. Results: A conserved arginine residue in the SBP is essential for the high affinity and carboxylate specificity of the TRAP transporter. Conclusion: The arginine/carboxylate interaction in TRAP SBPs restricts substrate range to carboxylate-containing substrates. Significance: The study reveals the mechanism by which a key bimolecular interaction underpins bacterial virulence.