You are hereTHE ROLE OF SECONDARY MESSENGER SYSTEM IN SIGNAL TRANSDUCTION

THE ROLE OF SECONDARY MESSENGER SYSTEM IN SIGNAL TRANSDUCTION


About Authors:
Mr. Salahuddin Mohammed
Associate Professor of Pharmacology, College of Health Sciences,
Department of Pharmacy, Mizan Tepi University,
Mizan Teferi, Ethiopia.
salahuddin_pharma48@yahoo.com

Introduction
Secondary messenger system is a part of cellular signaling process in which proteins of different kind are activated through generation of diffusible signaling molecules. The activated proteins then participate in a cellular response.
Second messengers are produced catalytically in response to the extracellular signals (primary messengers) and amplify their response, thus second messengers are a part of signal transduction cascades.

REFERENCE ID: PHARMATUTOR-ART-2031

In the transduction process, extracellular signal is passed from one intracellular molecule to another through the secondary messengers until al cellular behavior alters and the cytoskeleton is tweaked into new configuration.

G-protein Linked Receptor activation
G-protein linked receptors activate a class of membrane bound proteins which then migrates in the plane of plasma membrane initiating the cascade effects. This results in enzymatic alteration and generates host of additional signals, called as second messengers.


Figure 2: G-Protein receptor activation

· When the G-protein is activated it dissociates in to two signaling proteins.

· After the regulation of the target protein is completed, the G-protein α subunit switches off by hydrolyzing the bound GTP into GDP by GTPase. Then the reassociation of α and βγ complex takes place making theG-protein ready to couple with other receptor.


Figure 3: Activation cycle of G-proteins by G-protein-coupled receptors

Source by Sven Jähnichen

REQUIREMENTS FOR A COMPOUND TO ACT AS A SECOND MESSENGER

  • During hormone-receptor binding, concentration of second messenger should increase in order to exert the biological effect.
  • When the hormone is removed, the concentration of second messenger and the biological response shown by the hormone should decrease in concentration and activity.

type of intracellular signaling molecules

They are produced depending upon the interaction of the G-proteins with target enzymes as given below:


S.No


TARGET ENZYME


INTRACELLULAR SIGNALING MOLECULE PRODUCED

1.

Adenylyl cyclase

Cyclic AMP

2.

Phospholipase C

Inositol triphosphate

3.

Phospholipase C

Diacylglycerol

4.

Guanylyl cyclase

Cyclic GMP

Table 1: Types of Intracellular signalling molecules

I. CYCLIC AMP AS A SECONDARY MESSENGER

Cyclic-3’,5’-adenosine monophosphate is second messenger in intracellular signaling cascade. Wide variety of exogenous stimuli, such as hormones , neurotransmitters, physical and chemical signals control the intracellular level of cyclic nucleotides by regulating the enzyme systems directly or indirectly. These physiological effects are exerted through binding to a number of proteins which includes cyclic nucleotide dependant protein kinases, cyclic nucleotide gated channels and cyclic nucleotide-regulated phosphodiesterases.The phosphorylated state of various proteins and cyclic nucleotides are controlled by extracellular signals.

The regulatory mechanism of adenylyl cyclase is a typical G-protein dependant signal transduction.


Figure 4: Cyclic AMP activation

Source: universe-review.ca/F11-monocell.htm

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