Hydrophobic charge induction chromatography (HCIC) with 4-mercaptoethyl-pyridine (MEP) as the ligand has been proved to be effective for the separation of antibodies from different feedstocks. In the present work, the methods of molecular simulation are introduced to study the interactions between MEP and IgG. Firstly, molecular docking is used to identify the potential binding sites around the protein surface of Fc Chain A of IgG, and 12 potential binding sites are found. Then 6 sites are further studied using the molecular dynamics simulations. The results indicate that MEP ligand tends to bind on the hydrophobic area of Fc Chain A surface. At neutral conditions, MEP can bind stably on the site around TYR319 and LEU309 of Fc Chain A, which shows obviously a pocket structure with strong hydrophobicity. The analysis of trajectory reveals that hydrogen bonds exist between MEP and the former two amino acids around the simulation period. The binding of MEP to other sites are relatively unstable, and depends on the initial binding modes of MEP. When the pH lowers to 4.0, it can be found that MEP bound formerly on the Fc Chain A departs quickly due to the electrostatic repulsion, weaker hydrophobic interaction and the disappearance of hydrogen bonds. With the aids of molecular simulations, the separation mechanism of HCIC is verified from the view of molecular interactions-the binding with hydrophobic interactions at neutral condition and the desorption with electrostatic repulsion at acid condition.

Key words: 4-mercaptoethyl-pyridine, IgG, hydrophobic charge induction chromatography, binding mode, molecular simulation