The Protein Data Bank or PDB is the largest public repository of tridimensional structures of biological macromolecules. Most of them are proteins, but about 10% of the entries involve nucleic acids either pure or as a complex with proteins (see statistics). The PDB is certainly the most important database for all structural biologists and structural bioinformaticians.
An entry of the database is available in different formats. The original and still most popular format is the PDB format.
Referencing a structure from the PDB
A PDB identifier is case-insensitive 4-character code. It starts with a single digit and continues with a sequence of 3 alphanumeric characters. For instance 1crn, 2pel, 1MBA are valid PDB identifiers.