P1 Shake-and-Bake: can success be guaranteed?

The multi-trial direct-methods procedure known as Shake-and-Bake has been a pplied to three small proteins (alpha-1 peptide, vancomycin and lysozyme) t hat crystallize in space group P1. Phase refinement was accomplished throug h parameter-shift optimization using both the cosine and exponential forms of the minimal function. By extending error-free data to sufficiently high resolution, 100% convergence of trial structures to solution could be achie ved in all three cases by using the exponential minimal function and a shif t angle in the range 130-150 degrees. These results suggest optimum paramet ers for other P1 structures and emphasize the importance of collecting data to the highest possible resolution.