Finding crystal structures of peptides by random search and evolutionary algorithms.

Structures of crystalline peptides can be established using a special computer program, PTRY, which needs only limited diffraction data, the lattice constants, space group and primary structure. Crystal structures can be found by doing a random search in the internal-coordinate space and 'combinations' among the plausible solutions found according to the genetic rules ( crossover and mutation). PTRY, which also performs structural refinement, is simple and user friendly. Because only limited diffraction data are needed, data from powder diffraction spectra could be used, as well as single-crystal data.