STRUCTURE OF BOVINE GAMMA-B-CRYSTALLIN AT 150-K

X-Ray diffraction data have been collected from a single crystal of bo vine gammaB-crystallin, a lens specific protein, cryo-cooled to 150 K. The data extend and are measurable to 1.2 angstrom resolution. A prel iminary refinement, undertaken in the resolution range 8.D-2.0 angstro m indicates that the structure of the protein is essentially unchanged from that determined at 293 K and at 1.47 angstrom resolution. Howeve r, the sultydryl residues at 18 and 22 are in the fully reduced state in the low-temperature structure. The solvent structure is more clearl y defined at 150 K and some 255 water molecules have been located comp ared 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 wa ter molecules, with greater order, are observed in the second hydratio n shell at 150 K.