part_of part of part of signaling receptor binding signal transduction signaling receptor activator activity receptor ligand activity 2010-09-13T04:51:59Z GO:0048018 GO:0071884 https://github.com/geneontology/go-ontology/issues/14220 mah molecular_function receptor agonist activity vitamin D receptor activator activity signaling molecule signaling receptor ligand activity The activity of a gene product that interacts with a receptor to effect a change in the activity of the receptor. Ligands may be produced by the same, or different, cell that expresses the receptor. Ligands may diffuse extracellularly from their point of origin to the receiving cell, or remain attached to an adjacent cell surface (e.g. Notch ligands).