Improvements in lysozyme crystal quality via temperature-controlled growthat low ionic strength

In previous work, large high quality crystals of tetragonal lysozyme were g rown using constant supersaturation control (CSC) growth algorithms. Workin g toward the goal of inducing increased temperature sensitivity in protein crystallization, these results have been extended to low ionic strength sys tems using salts such as NaSCN and NaNO3 in lieu of NaCl. Using the combina tion of calorimetrically-determined growth rate parameters and constant sup ersaturation temperature control algorithms; large, well formed, single cry stals have been grown in NaSCN and NaNO3 buffer systems. The improvement in quality of these lysozyme crystals upon employing temperature controlled g rowth is striking. When compared to crystals grown using more traditional m ethods these crystals are quite large, and show few, or no, obvious defects . Preliminary crystal quality assessment via X-ray diffraction studies are encouraging. A single monoclinic CSC grown crystal had an average signal to noise ratio of 8.4 at a resolution of 1.62 Angstrom. In addition, this cry stal showed excellent resistance to radiation damage and continued to diffr act well after more then 45 h of continuous beam exposure. (C) 2001 Elsevie r Science B.V. All rights reserved.