Molecular Insight intothe Ligand–IgGInteractions for 4-Mercaptoethyl-pyridine Based Hydrophobic Charge-InductionChromatography.

Hydrophobic charge-induction chromatography (HCIC) with4-mercaptoethyl-pyridine(MEP) as the ligand is a novel technology for antibody purification.In the present work, the molecular simulation methods were used toinvestigate the interactions between MEP ligand and Fc fragment ofIgG (Fc-A). Six ligands with different structures of spacer arm werestudied with molecular docking and dynamics simulation at neutraland acidic pH. The binding modes and the interaction energies wereanalyzed. The results indicated that all ligands tested could bindinto the selected pocket on the CH2domain of Fc-A at neutralpH. The pyridine ring on the top of MEP ligands acts as a major roleto provide the hydrophobic association and hydrogen bond for the ligand–IgGbinding; meanwhile, the sulfone group on the spacer arm might formthe additional hydrogen bond and enhance the binding of ligand ontothe surface of IgG. The replacements of thioether sulfur atom on thespacer arm with either nitrogen or oxygen atom seem to have littleinfluence on the binding. The influences of pH on the ligand–IgGinteractions were also studied with the molecular dynamics simulation.It was found that MEP ligands would departed from the surface of Fc-Aat low pH due to the electrostatic repulsion. The ligands with a sulfonegroup on the spacer arm would weaken the electrostatic repulsion andneed more acidic conditions for the departing of ligand. The molecularsimulation results were in agreement with some experimental observations,which would be useful to elucidate the molecular mechanism of HCICand design a novel ligand to improve the efficiency of antibody separation. [ABSTRACT FROM AUTHOR]