Refined Structure of the Monoclonal Antibody HyHEL-5 with its Antigen Hen Egg-White Lysozyme

The crystal structure of the complex of the antibody Fab, HyHEL-5, with its antigen, hen egg-white lysozyme, has been refined at 2.65 Å resolution to an R value of 0.196. The resulting model has significantly better stereochemistry than the previously reported model of the complex, PDB reference 2HFL, and sufficiently improved phases, permitting the reliable location of a number of water molecules. No major conformational differences are observed between this structure and that previously reported, although small differences occur throughout the complex. 82 water molecules have been assigned, of which three are in the antibody-antigen interface involved in a hydrogen-bonding network. Three other waters are trapped within the interface between V_H and V_L and a fourth water molecule is observed near the interface but buried below the lysozyme surface as observed in crystal structures of lysozyme alone.