Biological Assembly files for large structures


Biological assembly files for large structures are now available for download from the Structure Summary page in the PDBx/mmCIF format. These files are also available on the FTP site ( The PDBx/mmCIF format has no restrictions on the number of atoms and chains and can hold biological assemblies of any size.
The biological assembly is the macromolecular assembly that has either been shown to be or is believed to be the functional form of the molecule. For more information, see PDB-101’s biological assembly tutorial.

RCSB PDB News Image"Download files" menu for a large structure PDB ID 5FDV. In this case, the asymmetric unit contains two copies of the ribosome. They are represented as two biological assemblies files: 5fdv-assembly1.cif.gz and 5fdv-assembly2.cif.gz.

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