Matthew A. Warkentin, and Robert E. Thorne
Physics Department,
Cornell
University
Abstract:
We have measured unit cell parameters, mosaicities, B-factors, crystal perfection, and radiation sensitivity for four
model systems -- Lysozyme, Trypsin, Thaumatin and Ribonuclease A -- as a function of temperature. Unlike in
previous temperature-dependent studies, data is continuously collected from an individual crystal as it cools from 300
K to 100 K. B factors and mosaicity increase and large scale crystal perfection (as probed by X-ray topography)
degrades between 240 K and 180 K. These parameters show more modest evolution between 180 K and 100 K,
where solvent and protein motions have frozen out. Similarly, most of the decrease in radiation sensitivity occurs
between 240 K to 180 K. This confirms that the glass transition in the solvent + mobile protein system is responsible
for the dramatically increased crystal lifetimes at 100 K. Radiation damage studies may thus allow quantitative study
of solvent and protein motions.
