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.
loop_ _struct_biol.id _struct_biol.details 1 ; significant deviations from twofold symmetry exist in this dimeric enzyme ; 2 ; The drug binds to this enzyme in two roughly twofold symmetric modes. Hence this biological unit (2) is roughly twofold symmetric to biological unit (3). Disorder in the protein chain indicated with alternative ID 1 should be used with this biological unit. ; 3 ; The drug binds to this enzyme in two roughly twofold symmetric modes. Hence this biological unit (3) is roughly twofold symmetric to biological unit (2). Disorder in the protein chain indicated with alternative ID 2 should be used with this biological unit. ;