An introduction to biological units in the PDB archive is now accessible at www.rcsb.org/pdb/biounit_tutorial.html. This useful guide offers detailed explanations and examples of the asymmetric unit and the biological molecule, indicates where information about the biological unit can be found in PDB and mmCIF coordinate files, and describes how the biological unit files in the PDB have been derived.
The RCSB PDB offers images and coordinates for the complete
biological unit of crystallographic entries in the archive. The
biological molecule, or biological unit, is the macromolecule that
has been shown to be or is believed to be functional. When
crystallographic structures are deposited into the PDB, the primary
coordinate file generally contains one asymmetric unit--the
smallest portion of a crystal structure to which crystallographic
symmetry can be applied to generate one unit cell. In some cases,
the asymmetric unit differs from the biologically active molecule.
The RCSB PDB provides data on biological units to further an
understanding of molecular function.
The biological unit tutorial is also linked from the View Structure
and Download/Display File sections of the Structure Explorer page,
as well as under PDB WWW User Guides. For more information, please
send inquiries to firstname.lastname@example.org.
The RCSB PDB (citation) is managed by two members of the Research Collaboratory for Structural Bioinformatics:
RCSB PDB is a member of the
The RCSB PDB is funded by a grant (DBI-1338415) from the
National Science Foundation, the
National Institutes of Health, and the
US Department of Energy.