Automated tracing of electron-density maps of proteins

The tracing of experimental electron maps in the field of protein crystallography is not a rate-limiting step for structure elucidation, but does represent the process that requires the most expertise and user time. This paper presents a method for automatically tracing the electron-density maps of proteins which can reliably generate a C^α trace for protein maps with data in the resolution range 1.5–4 Å. The number of C^α atoms placed and the precision of atom placement depends on the quality of the map, but even with poor maps (FOM ≃ 0.5) the algorithm can provide a significant saving in time over conventional methods of interpretation. The interpretation of six experimental maps is presented at different resolutions and levels of phase error; these show that data with an FOM of 0.7 or better can be entirely traced with no user intervention.