What is a PDB ID?

Each structure in the PDB is represented by a 4 character identifier of the form [0-9][a-z,0-9][a-z,0-9][a-z,0-9]. For example, 4HHB, 9INS are identification codes for PDB entries for hemoglobin and insulin. Many of PDB WWW pages, including the PDB home page, allow you to enter a PDB ID and retrieve information for the corresponding structure. Historically, 30% of queries to the PDB sites are of this type.