Structure of bovine γB-crystallin at 150 K

X-Ray diffraction data have been collected from a single crystal of bovine γB-crystallin, a lens specific protein, cryo-cooled to 150 K. The data extend and are measurable to 1.2 Å resolution. A preliminary refinement, undertaken in the resolution range 8.0-2.0 Å indicates that the structure of the protein is essentially unchanged from that determined at 293 K and at 1.47 Å resolution. However, the sulfydryl residues at 18 and 22 are in the fully reduced state in the low-temperature structure. The solvent structure is more clearly defined at 150 K and some 255 water molecules have been located compared to 230 from the 293 K refinement. Over 90% of the water molecules which make three or more hydrogen bond contacts with a single protein molecule are conserved at the two temperatures. A larger number of water molecules, with greater order, are observed in the second hydration shell at 150 K.