An Eye Lens Protein-Water Structure: 1.2 Å Resolution Structure of γB-Crystallin at 150 K

γβ‐crystallin is a structural protein of the eye lens with a role in the maintenance of an even distribution of protein and water over distances around the wavelength of light, preserving lens transparency. The structure of the 174‐residue bovine protein has already been determined at room temperature to 1.47 Å resolution. By flash freezing the protein crystals, data have now been collected to a nominal resolution limit of 1.2 Å as radiation damage was essentially eliminated. The protein‐water model has been refined against this data using the program RESTRAIN converging to an R factor of 18.5% with all data. Atomic positions are clearly indicated in the electron‐density maps. Discrete bimodal disorder has been visualized for a few side chains. Out of a total of 498 water molecules present in the crystal asymmetric unit, 394 have been modelled and refined at unit occupancy. The solvent structure is extremely well ordered with an average B value of 23.4 Å2. Partially occupied sites have been identified where disorder in the protein induces concomitant disorder in the local solvent structure. The solvent structure covers 97% of the solvent‐exposed surface of the protein in the crystal. 126 water molecules are distributed in second and higher hydration shells. There are networks of hydrogen‐bonded solvent extending up to 64 molecules in a network, comprising trimers and tetramers as well as five‐ and six‐membered water‐ring structures. The hydration of the protein surface is dominated by arginine and aspartate side chains. Extensive cages of highly ordered solvent molecules are also observed around exposed non‐polar groups.