The biological process by which all herbs, drugs and foods produce their effects is through the process of receptor binding.

The effect of the aforementioned substances is to stimulate the natural transmitters that instill euphoria, improve mood, dull pain or in some other way cause a feeling of gratification.

Olfactory and gustatory stimuli for example, interact with their corresponding receptors in the nose and mouth to produce the senses of smell and taste.

 

Nature regulates the supply of neurotransmitters in the body and their effects through a type of receptor known as the G protein-coupled receptor (GPCR).

The GPCR is named for its ability to activate G proteins.

The receptor, once bound, splits G-proteins into two active parts, an alpha subunit and a beta-gamma subunit.

The GPCR is a large family of proteins whose structure spans the entire width of a cell’s membrane. This gives the GPCR access to both the internal and the external environment of the cell. These trans-membrane receptors can sense molecules outside the cell and activate the internal network as well.  Because of this dual activity, the G-protein-coupled receptors have become a prime target of drug research

The ligands that bind and activate the GPCR vary in size from small molecules to large proteins These ligand emanate from odors, taste, light, inflammation and immunity. These receptors can also bound to hormones, neurotransmitters and neuropeptides.

 

The G protein-coupled receptor is made up of seven membrane-spanning zones. These are the binding domains of the receptor. These are the sites than can be activated by an external ligand to signal a conformational change, or activation of the transmembraneous protein.

 

The G protein-coupled receptor is the design of choice for light and smell. These receptors provide the binding sites and consequently trigger the signals sent out by a library of chemical agents, growth factors and neuropeptides.

Include in this library are the compounds involved with hunger and appetite like leptin and neuropeptide Y. Other GPCRs include the regulators of reproduction like follicle-stimulating hormone and gonadotropic-releasing hormone. There are still others that effect metabolism like glucagon and thyrotropin-releasing hormone.

 

Inflammation is mediated via the activity of GPCRs and an assortment of prostanoids, chemotactic agents, leukotrienes and anaphylatic factors..

G-protein coupled receptors also bind with vasoactive compounds to regulate blood vessel diameter, hence blood pressure, as well as vasopressin to regulate water balance.

G-protein coupled receptors in the brain bind with sensory signals as well as native opioids, and the neurotransmitters, dopamine and serotonin.

 

G-protein research has revealed a great deal about the way Nature simplified the process of regulatory control. The GPCR is the most elegant example of its systems of on and off switches. In the case of the G protein, the same molecule has multiple sites for binding. It the orchestration of these bindings that determines the end result.

 

Cell Signaling

In order for biological activities to occur, chemical reactions within the cell must occur. The initiation of these reactions is accomplished via receptors that are embedded in the plasma membrane of cell.

Most receptors cross the membrane so that binding sites are found exposed to the external environmen and ready to receive instructions via the ligands that they bind to.

Ligands are circulating in the blood based on local conditions. Examples of ligands include cytokines and growth factors, which are produced and act locally or hormones which are released by endocrine glands, under the control of the brain.

Having sites face the internal contents of the cell provides a mechanism for those instructions to be carried out. This is known as the ‘second messenger’ mechanism by which instructions are carried out.

The type of receptor on the cell is a function of the role of the cell. Steroid receptors and G-Protein-Coupled Receptors (GPCRs) are two major types of receptors. They operate on a signaling system that follows one of many pathways.

 

The changes that occur often effect the metabolic system of the cell. For example, the increased glycogenolysis or release of sugar the occurs when liver cells are exposed to adrenaline, is due to the binding of the hepatocyte receptor and the hormone.

 

G-Protein-Coupled Receptors (GPCRs)

G-protein coupled receptors can also produce change in the electrical charge of the membrane allowing movement across them or alter gene expression within the nucleus. 

G-Protein-coupled receptors are transmembrane proteins that cross through the plasma membrane seven times. Ligands are able to alter gene expression by binding with GPCRs. Hormones and other ligands affect DNA transcription. They include the neurotransmitters serotonin and GABA.

Once the ligand binds to a site (on the extracellular portion of the receptor), activation of a G protein takes place. The G-protein activation is followed by increased production of a "second messenger". The most common of these are cyclic AMP.