All protein structural data was extracted from the Brookhaven Protein Data Bank
(PDB) [9]. The PDB acts as a repository for macromolecular
structure information, primarily the results of X-ray crystallographic
analysis. Each molecular structure (e.g. a protein structure) is stored in an
individual flat file. The file entry contains the coordinates in a
Cartesian coordinate system for every atom in the structure. Additional
information regarding the experimental procedure used is also included together
with the source of the biological material that has been analysed.