Ligand (biochemistry)

In <a href="/facts/Biochemistry/fa2pWEBp">biochemistry</a> and <a href="/facts/Pharmacology/4Rx8s7Ie">pharmacology</a>, a ligand is a <a href="/facts/Chemical_substance/EWcXU41d">substance</a> that forms a <a href="/facts/Complex_(chemistry)/1tCyeQUm">complex</a> with a <a href="/facts/Biomolecule/DGvFzN7R">biomolecule</a> to serve a biological purpose. The etymology stems from Latin ligare, which means 'to bind'. In protein-ligand binding, the ligand is usually a <a href="/facts/Molecule/N9ljSfFq">molecule</a> which produces a <a href="/facts/Cell_signaling/6oYAVP9I">signal</a> by <a href="/facts/Molecular_binding/cBnorUC5">binding</a> to a <a href="/facts/Binding_site/gd9r9Rw7">site</a> on a target <a href="/facts/Protein/Jxmagu3E">protein</a>. The binding typically results in a change of <a href="/facts/Conformational_isomerism/JflrT5Ws">conformational isomerism</a> (conformation) of the target protein. In DNA-ligand binding studies, the ligand can be a small molecule, <a href="/facts/Ion/3bePpDna">ion</a>, or <a href="/facts/Protein/Jxmagu3E">protein</a> which binds to the <a href="/facts/Nucleic_acid_double_helix/XHeMuslB">DNA double helix</a>. The relationship between ligand and binding partner is a function of charge, <a href="/facts/Hydrophobe/Ifya0CXQ">hydrophobicity</a>, and molecular structure.
Binding occurs by <a href="/facts/Intermolecular_force/xIcFMvL7">intermolecular forces</a>, such as <a href="/facts/Ionic_bond/R6nUJI5u">ionic bonds</a>, <a href="/facts/Hydrogen_bond/85V86IIg">hydrogen bonds</a> and <a href="/facts/Van_der_Waals_force/jyGU8Vh9">Van der Waals forces</a>. The association or <a href="/facts/Docking_(molecular)/IKzf94wQ">docking</a> is actually reversible through <a href="/facts/Dissociation_(chemistry)/gDRGdeSN">dissociation</a>. Measurably irreversible <a href="/facts/Covalent/EzMLf3Pz">covalent</a> bonding between a ligand and target molecule is atypical in biological systems. In contrast to the definition of <a href="/facts/Ligand/6etB3qeW">ligand</a> in <a href="/facts/Metalorganic/WFv2Ypum">metalorganic</a> and <a href="/facts/Inorganic_chemistry/ErD6ypnb">inorganic chemistry</a>, in biochemistry it is ambiguous whether the ligand generally binds at a <a href="/facts/Metal/PT8hNX6R">metal</a> site, as is the case in <a href="/facts/Hemoglobin/RsD1MzYA">hemoglobin</a>. In general, the interpretation of ligand is contextual with regards to what sort of binding has been observed.
Ligand binding to a <a href="/facts/Receptor_(biochemistry)/tjTAC76a">receptor protein</a> alters the conformation by affecting the three-dimensional shape orientation. The conformation of a receptor protein composes the functional state. Ligands include <a href="/facts/Substrate_(biochemistry)/6MnaV19h">substrates</a>, <a href="/facts/Enzyme_inhibitor/MkFwGXHJ">inhibitors</a>, <a href="/facts/Activator_(proteomics)/soAFcLGS">activators</a>, <a href="/facts/Lipid-gated_ion_channels/GAU2oUJK">signaling lipids</a>, and <a href="/facts/Neurotransmitter/LlpYFSU3">neurotransmitters</a>. The rate of binding is called affinity, and this measurement typifies a tendency or strength of the effect. Binding affinity is actualized not only by <a href="/facts/Host%25E2%2580%2593guest_chemistry/q62EsHeX">host–guest</a> interactions, but also by solvent effects that can play a dominant, <a href="/facts/Steric_effects/TnX5c8HG">steric</a> role which drives <a href="/facts/Non-covalent_interactions/J0pnJCe8">non-covalent binding</a> in solution. The solvent provides a chemical environment for the ligand and receptor to adapt, and thus accept or reject each other as partners.
<a href="/facts/Radioligand/BD7LXsdM">Radioligands</a> are <a href="/facts/Radioisotope/5WpCfbdq">radioisotope</a> labeled compounds used <a href="/facts/In_vivo/kWcWyl6f">in vivo</a> as <a href="/facts/Radioactive_tracer/0210Jncn">tracers</a> in <a href="/facts/Positron_emission_tomography/5SmcW6qz">PET</a> studies and for <a href="/facts/In_vitro/evp3hAX6">in vitro</a> binding studies.

Ligand (biochemistry) open-in-new

Ligand (biochemistry)