Renumbering PDB files

From Proteopedia

Chemical groups (residues) in atomic coordinate files are numbered. For polymers (protein, DNA, RNA), the amino acid and nucleotide groups are given sequence numbers. For non-polymer groups (hetero groups in PDB terminology), the numbers are arbitrary. Unfortunately, the wwPDB allows arbitrary numbering which may be frustrating when comparing structures of similar macromolecules. See examples at Unusual sequence numbering.