W0195

The Shake-and-Bake Structure Determination of Triclinic Lysozyme. Ashley M. Deacon^a, Charles M. Weeks^b, Russ Miller^b,c and Steven E. Ealick^a, ^aDepartment of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY 14853, ^bHauptman-Woodward Medical Research Institute, Inc., 73 High Street, Buffalo, NY 14203-1196, ^cDepartment of Computer Science , State University of New York at Buffalo, NY 14260, USA

The computer program SnB (Shake-and-Bake) has been used to determine the crystal structure of triclinic lysozyme, ab initio, from 0.85 Å resolution native data alone. The asymmetric unit contains 1001 non-H protein atoms and approximately 200 bound water molecules. This is the largest structure determined so far by the SnB program. Initial experiments, using default SnB parameters derived from studies of smaller molecules, were unsuccessful. These experiments resulted in electron-density maps that were dominated by a single large peak. This problem was overcome by considering the choice of protocol used during the parameter-shift phase refinement. When each phase was subjected to just a single shift of 157.5 degrees during each SnB cycle, 22% of random trials yielded correct solutions within 750 cycles. This success rate is much higher than that typically observed, even for much smaller structures.