Crystallographic relationship between human and hen-egg lysozymes. II. Weighting of electron-density maps phased from an incomplete model structure and comparison with map obtained by isomorphous replacement

Methods suitable for completing and refining a protein structure are investigated both theoretically and with human and hen lysozymes as an example. Sim (or Woolfson) weighting and the α-synthesis are compared with unweighted maps, and while the former is an improvement over unweighted maps, the α-synthesis is less clearly an improvement. Both WFo exp (iαc) and difference maps were found to be useful, and a comparison between the isomorphous replacement map of human lysozyme and our maps based on hen lysozyme was encouraging.