PDB information. For every experimental structure in the PDB, some basic information is provided, regardless of the presence or absence of a small molecule ligand and regardless whether affinity data are already available or not. This includes the name of the protein or protein class (as given in the header information of the PDB file), the E.C. number in case of an enzyme (if available), the source of the protein, the resolution of the crystal structure, and the name of the authors of the PDB structure. In addition, each PDB code is linked to the following external databases: PDB, Relibase, MSD, SCOP, PDBsum