Binding properties of antimicrobial agents to dipeptide terminal of lipid II using surface plasmon resonance

We developed a surface plasmon resonance (SPR) assay to estimate the interactions of antimicrobial agents with the dipeptide terminal of lipid II (d-alanyl-d-alanine) and its analogous dipeptides (l-alanyl-l-alanine and d-alanyl-d-lactate) as ligands. The established SPR method showed the reproducible immobilization of ligands on sensor chip and analysis of binding kinetics of antimicrobial agents to ligands. The ligand-immobilized chip could be used repeatedly for at least 200 times for the binding assay of antimicrobial agents, indicating that the ligand-immobilized chip is sufficiently robust for the analysis of binding kinetics. In this SPR system, the selective and specific binding characteristics of vancomycin and its analogs to the ligands were estimated and the kinetic parameters were calculated. The kinetic parameters revealed that one of the remarkable binding characteristics was the specific interaction of vancomycin to only the d-alanyl-d-alanine ligand. In addition, the kinetic binding data of SPR showed close correlation with the antimicrobial activity. The SPR data of other antimicrobial agents (e.g., teicoplanin) to the ligands showed correlation with the antimicrobial activity on the basis of the therapeutic mechanism. Our SPR method could be a valuable tool for predicting the binding characteristics of antimicrobial agents to the dipeptide terminal of lipid II.