THE SHAKE-AND-BAKE STRUCTURE DETERMINATION OF TRICLINIC LYSOZYME

The crystal structure of triclinic lysozyme, comprised of 1,001 non-H protein atoms and approximate to 200 bound water molecules, has been d etermined ab initio (using native data alone) by the ''Shake-and-Bake' ' method by using the computer program SnB, This is the largest struct ure determined so far by the SnB program, Initial experiments, using d efault SnB parameters derived from studies of smaller molecules, were unsuccessful. In fact, such experiments produced electron density maps dominated by a single large peak. This problem was overcome by consid ering the choice of protocol used during the parameter-shift phase ref inement. When each phase was subjected to a single shift of +/-157.5 d egrees during each SnB cycle, an unusually high percentage of random t rials (approximate to 22%) yielded correct solutions within 750 cycles , This success rate is higher than that typically observed, even for m uch smaller structures.