Shake-and-Bake applications using simulated reference-beam data for crambin.

The Shake-and-Bake method, as implemented in the computer program SnB, has been applied to simulated reference-beam data for the small protein crambin at several resolutions in the range 1.5-3.0 A. Sets of triplet invariants were generated having simulated mean triplet-phase errors from 0 to 60 degrees. Provided that these errors were no larger than 40 degrees, it was possible (at all resolutions tested) to find trial sets of individual Bragg phases with mean errors of 40-45 degrees. At 1.5 A, this could be achieved using only a single reference-beam data set. Peak picking provided useful phase constraints even at the lowest resolution tested. These results suggest that direct methods may be useful in conjunction with reference-beam data at resolutions lower than 1.2 A.