Pattern-recognition methods to identify secondary structure within X-ray crystallographic electron-density maps

The interpretation of macromolecular crystallographic electron-density maps is a difficult and traditionally a manual step in the determination of a protein structure. The visualization of information within an electron-density map can be extremely arduous owing to the amount and complexity of information present. The ability to see the overall fold and structure of the molecule is usually lost among all the detail, particularly with larger structures. This paper describes a novel method of analysis of electron density in real space that can determine the secondary structure of a protein within minutes without any user intervention. The method is able to work with poor data as well as good data at resolutions down to 3.5 Å and is integral to the functionality of QUANTA. This article describes the methodology of the pattern recognition and its use with a number of sets of experimental data.