Capturing the Flexibility of a Protein-Ligand Complex with Enhanced Sampling Techniques: Binding Free Energies from Umbrella Sampling, REST2, and Bias Exchange

The performance of the three popular enhanced sampling techniques Umbrella Sampling (US), Replica Exchange with Solute Tempering 2 (REST2), and Bias Exchange (BE) is tested on Major Histocompatibility Complex I (MHC I) binding an antigenic peptide. The configurational flexibility of peptide-MHC I complexes (pMHC I) is key to their immunological function and must therefore be captured thoroughly by the sampling techniques used to yield accurate thermodynamics of pMHC I. Here, we calculate the Potential of Mean Force (PMF) for the dissociation of the peptide N-terminus from the MHC I binding groove. We carefully analyze the statistical error of the resulting PMF and the sampling of the orthogonal degrees of freedom to assess how well the three sampling techniques used can handle large-scale configurational flexibility.