Fast ab initio calculation of solvent envelopes for protein structures

A fast and simple method has been developed for the ab initio calculation of low-resolution solvent envelopes for macromolecular structures. In essence, a sphere of point scatterers is moved through the asymmetric unit cell in a part random, part systematic search for the configuration which corresponds to the lowest R value. The spheres correspond to the solvent regions in the cell. The program has been shown to work successfully for a number of test structures in a variety of space groups. No prior knowledge of the structures is needed, and c.p.u. requirements are extremely modest.