XmlmmCIF equivalent: struct_biol Data items in the STRUCT_BIOL category record details about the structural elements that form each structure of biological significance. A given crystal structure may contain many different biological structures. A given structural component in the asymmetric unit may be part of more than one biological unit. A given biological structure may involve crystallographic symmetry. For instance, in a structure of a lysozyme-FAB structure, the light and heavy chain components of the FAB could be one biological unit, while the two chains of the FAB and the lysozyme could constitute a second biological unit. XmlmmCIF equivalent: struct_biol/details A description of special aspects of the biological unit. XmlmmCIF equivalent: struct_biol/pdbx_parent_biol_id An identifier for the parent biological assembly if this biological unit is part of a complex assembly. EBI Item. Accesible surface area of the assembly as calculated by PQS EBI Item. Whether the assembly contains just one entity (HOMO) or more than one entity (HETERO) EBI Item. The oligomeric state of the assembly, e.g. MONOMERIC, DIMERIC EBI Item. Number of chains in the assembly XmlmmCIF equivalent: struct_biol/id The value of _struct_biol.id must uniquely identify a record in the STRUCT_BIOL list. Note that this item need not be a number; it can be any unique identifier.