Interpretation of very low resolution X-ray electron-density maps using core objects

A novel approach to obtaining structural information from macromolecular X-ray data extending to resolutions as low as 20 angstrom is presented. Following a simple map-segmentation procedure, the approximate shapes of the domains forming the structure are identified. A pattern-recognition comparative analysis of these shapes and those derived from the structures of domains from the PDB results in candidate structural models that can be used for a fit into the density map. It is shown that the placed candidate models can be employed for subsequent phase extension to higher resolution.