PDB identification code: Difference between revisions

Every molecular model ([[Atomic coordinate file|atomic coordinate file]]) in the [[Protein Data Bank]] (PDB) has a unique accession or identification code. These codes are always 4 characters in length. The first character is a numeral, while the last three characters can be either numerals or letters. In the past, the first character was always a numeral in the range 1-9. Although there appear to be no entries beginning with "0", its exclusion [http://www.rcsb.org/robohelp/index.htm#search_database/pdb_identifier.htm may have been relaxed].

There are over 400,000 possible 4-character PDB identification codes (419,904 or 466,560 if "0" is allowed as the first character). Thus, the ~89,000 entries in early 2013 have used up ~21% of the available codes. Someday a scheme that can accomodate more entries will be required, requiring revision of macromolecular visualization and modeling software programs that obtain data online, all of which, of necessity, currently require 4-character PDB codes.