Multimodal (MM) chromatography provides a powerful means to enhance the selectivity of protein separations by taking advantage of multiple weak interactions that include direct charge-charge interactions, hydrophobic assembly, interaction between dipoles, etc. In order to increase our understanding of such phenomena, the binding of proteins to model MM chromatographic surfaces was examined. The MM surface in our model was represented by a self assembled monolayer (SAM) presenting MM ligands with fixed surface density. In order to ascertain binding free energies, we followed two parallel approaches: (I) The first approach involved calculations of interaction energies that accounted for electrostatics, dispersion and hydrophobic interactions through the use of appropriate coarse grained force fields at various orientations of the protein with respect to the multimodal SAM surface. Using these theoretical interaction energies, binding maps were generated. (II) The second approach entailed all atoms molecular dynamics simulations along with umbrella sampling methods to ascertain the binding free energies of different faces of the protein. Because this method is computationally very expensive, two faces of the protein ubiquitin were tested. The free energy profiles thus obtained were compared to single molecule force spectroscopy experiments of the same faces of the protein, which showed qualitative similarities. The results from both approaches (I) and (II) were compared to determine if (a) the same preferred binding regions on the protein surfaces were identified and (b) the relative strength of binding in these regions were comparable. The latter approach serves as a calibration for the former which is computationally much less expensive and easy to use. This new modeling approach offers a computationally efficient tool for facilitating bioprocess development.

Binding of proteins to multimodal chromatographic surfaces: A molecular modeling perspective

249th National Meeting (2015)

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