cell signaling mechanism

1. Concept of agonists and antagonists in
receptor activation and inhibition and
significance in regulation of signaling.
BY – RAHUL KUMAR
M.Sc. LIFE SCIENCE
3RD SEMESTER
CUG/2014/1073

2. Objective:
 Ligand & its types
 Agonist & Antagonist
 Properties & Types of Agonist
 Properties & Types of Antagonist
 Significance in regulation of signaling

3. Classification of ligands:
• Ligands are classified by effect upon binding to the receptor.
LIGANDS
Agonist
Antagonist

4. Comparison between agonist & antagonist:
Agonist
• Derived from Latin word –
contender.
• Aids in the enhancement of an
action.
Antagonist
• Derived from Latin & Greek
words – competitor or
opponent.
• Opposes the action of agonist
and block the reception.

5. Properties of agonist:
 Acute Signaling
 Desensitization
 Sequestration
 Resensitization

6.  Receptors can be activated either by endogenous or
exogenous , leads to change in the biological response.
 Types of agonist-
a) Full agonist
b) Partial agonist
c) Inverse agonist

7. Full agonist – The ligands that increase the activity of the receptors &
produce the maximal response .
Ex.- Morphine ,mimics the action of endorphins at
opioid receptors.
Partial agonist – These ligands partially increase the activity of the
receptors but do not produce the maximal
response like full agonist even when present in excess
amount.
Ex.- Buspirone , is an anxiolytic drugs , used to treat an
anxiety disorder.

8. Inverse agonist – The ligands which decrease the activity of
an active receptors to their inactive state.
Ex.- Flumazenil drugs acts as a inverse agonist for the
GABA receptor & produce anxiogenic effect.

9. Properties of Antagonist :
 Site selectivity.
 Structural conformation – mimics with the natural ligand.
 Reduces the response.
 Effect may be temporary or permanent.

10. Competitive
Types of antagonist-
Reversible
Irreversible
Non-competitive

11.  Competitive antagonists – The antagonist competes with
the agonist for the orthosteric sites for binding to
the same receptor .
- The effect of the antagonist can be overcome by
increasing the concentration of the agonist.
Ex.- IL-1RA protein competes with IL-1 for binding to
the cell surface interleukin-1 receptor.

12.  Non-competitive antagonists : The antagonist binds at a
different site other than orthosteric site on the receptor.
- The effect of the antagonist cannot be overcome by increasing
the concentration of agonist.
Ex.- Binding of cyclothiazide with mGLUR1 receptor.

13.  Irreversible antagonists:
May or may not competes with the agonist for orthosteric sites for binding to
the receptor.
- Forms covalent bond to the site.
Ex.- Aspirin.

14. Significance of regulation in signaling:

16. REFERENCES -
The cell (5th Edition) Cooper & Hausman
Lehninger principle of biochemistry (5th Edition)
Principles & Techniques of Biochemistry & Molecular biology (7th Edition) by
Kleith Wilson & John Walker
Handbook of cell signaling Vol.1 (2nd Edition)

17. THANK YOU