New Features

Coming Soon: PDB Entries with Novel Ligands Distributed Only in PDBx/mmCIF and PDBML File Formats

09/12 wwPDB News

At current growth rates, we anticipate running out of three-character Chemical Component IDs by the end of 2023. After this point, the wwPDB will issue five-character alphanumeric accession codes for CCD IDs in the OneDep system. To avoid confusion with current four-character PDB IDs, four-character codes will not be used. Owing to limitations of the legacy PDB file format, PDB entries containing the new five character ID codes will only be distributed in PDBx/mmCIF and PDBML formats (see previous announcement).

In addition, wwPDB has reserved a set of CCD IDs: 01 - 99, DRG, INH, LIG that will never be used in the PDB. These reserved codes can be used for new ligands during structure determination so that they can be identified as new upon deposition and added to the CCD during biocuration.

wwPDB asks users and software developers to review code to remove any current limitations on CCD ID lengths, and to enable use of PDBx/mmCIF format files. Example files with extended CCD IDs are available via GitHub to assist code revisions. Information about the PDBx/mmCIF dictionary and file format is provided at

For any further information please contact us at

The number of available 3-character CCD IDs as of September 2023.The number of available 3-character CCD IDs as of September 2023.

New Features Index