ligandtarget

In pharmacology and biochemistry, a ligand-target interaction refers to the binding of a ligand to a biological macromolecule or nucleic acid that serves as a functional target. Ligands include endogenous signaling molecules, such as hormones and neurotransmitters, as well as synthetic or natural compounds used as drugs, toxins, or research tools. The binding event can modulate the target's activity, alter its conformation, or affect interactions with other cellular components.

Common targets include receptors (such as G protein-coupled receptors and ion channels), enzymes, transporters, and nucleic acids. Ligands are classified by their effect as agonists, antagonists, or inverse agonists, and by mechanism as orthosteric or allosteric ligands. They may act competitively at the primary binding site, or noncompetitively by stabilizing alternative conformations. In drug discovery, selecting ligands with suitable affinity, potency, selectivity, and drug-like properties is essential.

Key properties include binding affinity (Kd), potency (EC50 or IC50), efficacy, and kinetics (on and off rates). Selectivity refers to preference for the intended target over related proteins, while polypharmacology describes ligands that affect multiple targets. Pharmacodynamics describes the functional output of binding, and pharmacokinetics describes the ligand's distribution and fate in the body.

Characterization relies on experimental methods such as binding assays and structural techniques, as well as computational approaches including molecular docking and quantitative structure–activity relationship analyses. The ligand-target paradigm underpins drug discovery, toxicology, and systems pharmacology, informing target identification, lead optimization, and safety assessment.