Published December 04, 2023 by

Drug receptors: Types, Mechanism of Action


A receptor is a component of cell membranes that interacts and binds to a drug to initiate biochemical events leading to the drugs observed effects or to inhibit any specific physiological action in the body.

Drugs that bind to the receptor and initiates biological reactions in the body are known are agonist. On the other hand, drugs that inhibit the action of an agonist is known as antagonist. 

Nowadays, structural information of many receptor proteins are gained that has led to the developed molecular processes in drug-receptor interactions. 

A numerous numbers of receptor protiens have been discovered and their isolation, purification, cloning and sequence of amino acids has been established. Most of the receptors are protein in nature and some are glycoproteins. 

However, the signal transport process and mechanism of action of receptors are governed by a limited number of basic mechanisms. There are four super families of receptor proteins that covers most of the receptor proteins. The four super families are:

1. Ligand-gated ion channels

2. G-protein coupled receptors 

3. Intracellular receptors 

4. Tyrosine kinase linked receptors

Ligand-gated ion channels (ionotropic receptors)

These are membrane bound receptors that are directly linked to an ion channel. These are large multisubunit receptors containing 4-5 subunits. When open, they allows the passage of Na+,K+,Ca++,Cl–.

Ligand gated ion channels are classified into three families based on their molecular and protein structure criteria. 

01. "cys-loop" ligand gated ion channels 

E.g: 5-HT3,GABA-A,GABA-B receptors

02. Glutamate receptors 

E.g: kinate receptors, metabotropic receptors, NMDA receptors

03. ATP-sensitive P2X receptors.

Their function include mediating neurotransmitter responses to the central and peripheral nervous system, also maybe in non-excitable cells. However, ligand itself is not the substance that is transmitted into the cell. They function by facilitating the signal transmission in CNS or PNS. 

Example of Ligand-gated ion channel receptor drugs include: Acetylcohline, Histamine, Serotonin.

G-protein(Guanine nucleotide-rugulatory protein)  coupled receptors

These are membrane-bound receptors coupled to G-proteins. After the activation of G-proteins, a variety of biochemical signal transmission pathways may be activated. These are also known as metabotropic receptors.

In eukaryotes, G-protein coupled receptors are the most variable and largest group of membrane receptors. Researchers claimed that about one half of the marketed drugs acts by binding with GPCRs.

Functional mechanism include the following pathway 

Receptor binding :

Receptor binding 

Mechanism of action :

Example of G-protein coupled receptor drugs include: CASR, CALCR, BDKRB1, BDKRB2

Tyrosine Kinase-linked receptor

Tyrosine  kinase-linked receptor are membrane bound receptor containing intrinsic enzymatic function in their intracellular domain for many polypeptide growth factors, cytokines and hormones.There are 90 unique tyrosine kinase genes identified in human genome.

Tyrosine kinase are important mediators of signal transduction process,leading to cell proliferation, migration, Programmed cell death etc.Besides those they also play an important role in growth,motility, differentiation and metabolism.

Tyrosine kinases are a family of enzymes that catalyzes phosphorylation of select tyrosine residues in target protein by using ATP.  Here,three distinct process may occur including ligand-induced dimerization, activation of the  cytoplasmic kinase domain and linking the activated Tyrosine Kinase to cell signaling.

Example of such receptors are the fibroblast growth factor receptor and insulin-like growth factor receptors.

Intracellular receptor regulating gene transcription 

Intracellular receptor regulating gene transcription are also known as nuclear receptor which are located in the cytosol. 

These receptors function via their capacity to recognize and bind specific ligand (e.g. steroid hormones). Once stimulated by ligands, intracellular receptor translocate to the nucleus and initiate gene transcription as well as they may alter the gene expression. 

Example of this types of receptors are thyroid hormone, Vitamin D and the large group of steroid hormones including glucocorticoids, mineralocorticoids, and the sex steroid hormones.