Nuclear Magnetic Resonance at the Interface: Identifying Preferred Binding Regions in Multimodal Cation Exchange Chromatography using Functionalized Nanoparticles

Abstract

The Fc domain is an important component of complex molecules such as monoclonal antibodies (mAb) based biologics as well as fusion proteins and is highly conserved across a given class of mAbs. Recent work in our lab has shown the importance of specific domains towards binding for mAbs to multimodal (MM) cation exchange chromatographic systems. In this collaborative work, we employ a combination of Nuclear Magnetic Resonance (NMR) spectroscopy and Umbrella sampling simulations to develop a fundamental understanding of how multimodal ligands and surfaces interact with the Fc domain. We performed NMR titration experiments with isotopically labeled Fc and ∼15 nm diameter gold nanoparticles (Au NPs) functionalized with Self Assembled Monolayers (SAMs) presenting different MM ligands at different ligand densities. The results showed the interface of CH2 and CH3 domains and the hinge region to be preferred binding regions for interaction of Fc to MM ligand surfaces. These flexible regions on the protein surface which are rich in positive and aliphatic residues are important for the binding of Fc to MM ligand surfaces. Further, to shed light on the binding mechanisms, we performed umbrella sampling with the Fc held at key orientations above a SAM surface presenting MM ligands at relevant ligand densities similar to those tested experimentally. These simulations suggested that as the Fc was brought close to the surface, the residues near the hinge region first made contact with the surface followed by a tighter binding facilitated by interaction of His, Val, Leu and Ile residues at the interface of the CH2 and CH3 domains. This combined experimental and simulations approach enabled us to develop a molecular level understanding of the binding for complex biological products in MM CEX systems.