Macromolecular dictionary (mmCIF) version 2.0.09
Data items in the ENTITY category record details (such as chemical composition, name and source) about the molecular entities that are present in the crystallographic structure. Items in the various ENTITY subcategories provide a full chemical description of these molecular entities. Entities are of three types: polymer, non-polymer and water. Note that the water category includes only water; ordered solvent such as sulfate ion or acetone would be described as individual non-polymer entities. The ENTITY category is specific to macromolecular CIF applications and replaces the function of the CHEMICAL category in the CIF core. It is important to remember that the ENTITY data are not the result of the crystallographic experiment; those results are represented by the ATOM_SITE data items. ENTITY data items describe the chemistry of the molecules under investigation and can most usefully be thought of as the ideal groups to which the structure is restrained or constrained during refinement. It is also important to remember that entities do not correspond directly to the enumeration of the contents of the asymmetric unit. Entities are described only once, even in those structures that contain multiple observations of an entity. The STRUCT_ASYM data items, which reference the entity list, describe and label the contents of the asymmetric unit.Example:
Example 1 - based on PDB entry 5HVP and laboratory records for the
structure corresponding to PDB entry 5HVP.
loop_ _entity.id _entity.type _entity.formula_weight _entity.details 1 polymer 10916 ; The enzymatically competent form of HIV protease is a dimer. This entity corresponds to one monomer of an active dimer. ; 2 non-polymer 647.2 . 3 water 18 .
Mandatory category: no