Types of ligands

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In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose.

Ligands include:

Substrates

Inhibitors

Activators

Signaling lipids

Neurotransmitters

A ligand that can bind to and alter the function of the receptor that triggers a physiological response is called a receptor agonist.

Endogenous agonists:

In general, receptors for small molecule neurotransmitters such as serotonin will have only one endogenous agonist, but often have many different receptor subtypes (e.g. 13 different receptors for serotonin). On the other hand, neuropeptide receptors (e.g. opioid receptors) tend to have fewer subtypes, but may have several different endogenous agonists. This allows for a high degree of complexity in the body's signalling system, with different tissues often showing quite distinct responses to a particular ligand.

A physiological agonist is a substance that creates the same bodily responses but does not bind to the same receptor.

Examples of agonists:

  • acts as a 1alpha,25(OH)(2)D(3) superagonist of Vitamin D on Vitamin D receptor and exhibits both antiproliferative and prodifferentiating properties in vitro.
  • in Transport inhibitor response 1 (3c6o). Water molecules are shown as red spheres.
  • of human Bile acid receptor ligand-binding domain (deeppink) complex with non-steroidal agonist, nuclear receptor coactivator 1 peptide (cyan) and sulfate ions (PDB entry 3ruu). [1]

Ligands that bind to a receptor but fail to activate the physiological response are receptor antagonists.

  • participates directly in agonist/competitive antagonist binding, affects activation gating, and is the portion that forms the 'middle' layer.
in the structure of Glutamate receptor (GluA2).
The small molecule [2], was studied as a treatment for stroke because it had demonstrated neuroprotective efficacy in experimental models of stroke and tolerability in healthy volunteers; however, in a multicenter, double-blind, randomized, placebo-controlled phase II trial, it was found to have significant sedative effects in patients with acute stroke which precludes its further development as a neuroprotective agent[3].

Human CXCR4 receptor with cyclic peptide ligand (antagonist) CVX15 (PDB code 3oe0)

Drag the structure with the mouse to rotate

ReferencesReferences

  1. Akwabi-Ameyaw A, Caravella JA, Chen L, Creech KL, Deaton DN, Madauss KP, Marr HB, Miller AB, Navas F 3rd, Parks DJ, Spearing PK, Todd D, Williams SP, Wisely GB. Conformationally constrained farnesoid X receptor (FXR) agonists: Alternative replacements of the stilbene. Bioorg Med Chem Lett. 2011 Aug 11. PMID:21890356 doi:10.1016/j.bmcl.2011.08.034
  2. Turski L, Huth A, Sheardown M, McDonald F, Neuhaus R, Schneider HH, Dirnagl U, Wiegand F, Jacobsen P, Ottow E. ZK200775: a phosphonate quinoxalinedione AMPA antagonist for neuroprotection in stroke and trauma. Proc Natl Acad Sci U S A. 1998 Sep 1;95(18):10960-5. PMID:9724812
  3. Walters MR, Kaste M, Lees KR, Diener HC, Hommel M, De Keyser J, Steiner H, Versavel M. The AMPA antagonist ZK 200775 in patients with acute ischaemic stroke: a double-blind, multicentre, placebo-controlled safety and tolerability study. Cerebrovasc Dis. 2005;20(5):304-9. Epub 2005 Aug 30. PMID:16131799 doi:10.1159/000087929

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