A model of water structure inside the HLA-A2 peptide binding groove.

Based on molecular dynamics simulations, it is proposed that water within the binding groove of the human MHC class I molecule HLA-A2 plays a role in the formation of its complex with the influenza matrix protein (residues 58-66; GILGFVFTL) peptide. In these simulations, a loosely structured network of water molecules is present in the binding groove between the peptide and the MHC molecule, and may be important in completing the peptide-MHC interface. In two independent 400 ps simulations where groove-based water molecules were included, the peptide remained essentially in the conformation observed in the crystal structure. In contrast, in a 400 ps simulation in which no water molecules were placed between the peptide and the MHC molecule, the crystal structure conformation was rapidly lost. The basis for this behavior appears to be that the groove-based water molecules help to maintain the appropriate orientation of the Arg-97 side chain of HLA-A2 and, in turn, the conformation of the central part of the peptide.