About Asymmetric Unit
[About Asymmetric Unit]
Asymmetric Unitis used in either meaning of Crystal asymmetric unit or Non-Crystallographic asymmetric unit.
- Crystal Asymmetric Unit
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The crystal asymmetric unit is the smallest portion of a crystal structure to which symmetry operations can be applied in order to generate the complete unit cell (the crystal repeating unit). Structures analyzed by crystallographic methods are deposited in this structural unit. A crystal asymmetric unit is not always identical to the biological assembly and may in fact contain a portion of a biological assembly or multiple biological assemblies.
- Non-crystallographic Asymmetric Unit
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When a biomolecule is assumed to have a complete symmetry in its own structure, e.g. a virus's capsid, it is recommended to deposit the structure in the smallest unit (i.e. non-crystallographic asymmetric unit) to the PDB. To reconstruct the biological assembly, non-crystallographic symmetry operations should be applied to the deposited coordinates. Typical examples are a spherical virus with icosahedral symmetry or a rod-shaped virus with helical symmetry.
An image of an asymmetric unit is shown for deposited coordinates of an entry. For split entries, a complete asymmetric unit is obtained by combining each asymmetric unit.
- See RCSB contents for more details about Asymmetric unit, Biological assembly and Biological
assembly description in PDB data files.
(RCSB PDB-101) Looking at Structures: Introduction to Biological Assemblies and the PDB Archive
