Lexicon · NucLex for innovators
Ligand
Fully specified name: Ligand (concept)
An entity that binds to another entity, with meaning dependent on chemical or biological context.
- Scope note
- State what binds to what and under which conditions.
- Synonyms
- None recorded as true synonyms in this context.
- Monograph
- Radiopharmaceutical identity (planned; brief only)
- External mappings
- None recorded. In W0 no mapping to SNOMED CT® or any external authority is asserted for this entry. A future mapping record will carry source system, identifier, version, relation type, evidence, author, confidence where meaningful, and review state.
- Formal status
- Editorial entry only. It is not part of any released ontology and a prose edit here changes no formal definition.
Draft. This entry is an unreviewed draft. Its sources have not been checked by a named person and no domain reviewer has approved it. Treat every claim as provisional.
Notes
"Ligand" is a relational word. Nothing is a ligand on its own; something is a ligand of something else. The term is used in at least three disciplines with different partners in mind, and the ontology must record which is meant.
In coordination chemistry a ligand is an ion or molecule that donates electrons to a central metal atom. A radiochemist labeling a molecule with a metallic radionuclide uses a chelator whose donor groups are ligands of the metal. In pharmacology and molecular biology a ligand is a molecule that binds a receptor, enzyme, transporter, or other macromolecule. In the radiopharmaceutical literature "ligand" often names the whole targeting molecule that carries the radionuclide to a molecular target, which is why the phrase "radioligand therapy" appears.
These senses can coexist in one agent: the chelator is a ligand of the radionuclide, and the complete labeled molecule is a ligand of the biological target. A statement such as "the ligand binds" is incomplete until it says which entity binds which partner, with what measured affinity, in what assay or biological system, and under what conditions. NucLex therefore treats a ligand relationship as an interaction record with named participants rather than as a property of one molecule.