Data items in the STRUCT_CONN category record detail about the interactions between portions of structure. These can be hydrogen bonds, salt bridges, disulfide bridges, and so on. The NDB uses this category also to describe nucleic acid base pairing, mismatches and covalent modifier links. The value of _struct_conn.id must uniquely identify a record in the STRUCT_CONN list. Note that this item need not be a number; it can be any unique identifier.
hydrog1, hydrog2
covale_base1, covale_base2
covale_sugar1, covale_sugar2
covale_phosphate1, covale_phosphate2
link1, link2