classification of receptor and detail study about nuclear receptor and enzyme linked receptor by Kashikant Yadav

1. BY:KASHIKANT YADAV
M PHARMACY(PHARMACOLOGY)
CLASSIFICATION OF RECEPTOR
FAMILY AND MOLECULAR STRUCTURE
OF ENZYME LINKED RECEPTOR AND
NUCLEAR RECEPTOR

2. What is receptor
 Specialized areas of cell to which drugs get bound.
 drug targets/protein molecule usually found inside
or on the surface of a cell that receives chemical
signals from outside the cell.
 When such chemical signals bind to a receptor,
they cause some form of cellular/tissue response,
e.g. change in the electrical activity of the cell.

3.  Therefore, a receptor is a protein molecule that
recognizes and responds to endogenous chemical
signals.
 A molecule that binds to a receptor is called a ligand ,
and can be a peptide(short protein) or another small
molecule such as a
 neurotransmitter,
 hormone,
 pharmaceutical drug, or
 toxin.

5. Classification
 There are 2 types of receptors. Those are : Internal
& Cell surface receptor
i. Internal /Intracellular/Cytoplasmic
receptors : eg. Nuclear receptors
 found in the cytoplasm of the cell
 respond to hydrophobic ligand molecules
 Hydrophobic signaling molecules typically
diffuse across the plasma membrane
 interact with intracellular receptors in the
cytoplasm.

6. ii. Cell-surface /transmembrane receptors /
cell specific proteins
performs signal transduction,
converting an extracellular signal into an
intracellular signal.

7.  3 main components:
i. an external ligand-binding domain (extracellular
domain),
ii. a hydrophobic membrane-spanning region,
iii. an intracellular domain inside the cell.

8. There are three general categories of cell-surface
receptors:
1. Ion channel-linked receptors,
2. G-protein-linked receptors,
3. Enzyme-linked receptors.

10. Nuclear receptors
 a class of proteins found within cells that are
responsible for sensing steroid and thyroid
hormones
 have the ability to directly bind to DNA and regulate
the expression of adjacent genes
 hence these receptors are classified as transcription
factors

11.  A unique property of nuclear receptors that
differentiates them from other classes of receptors is
their ability to directly interact with and control the
expression of genomic DNA.
 As a consequence, nuclear receptors play key roles in
both embryonic development and adult homeostasis.

13. Structure of Nuclear receptors

14. Structure Nuclear receptors
(AB) Nterminal regulatory domain: Contains the
activation function 1 (AF1) whose action is
independent of the presence of ligand.
 The AB domain is highly variable in sequence
between various nuclear receptors

15. (C) DNAbinding domain (DBD): Highly
conserved domain containing two zinc fingers that
binds to specific sequences of DNA called hormone
response elements (HRE).
(D) Hinge region: Thought to be a flexible domain
that connects the DBD with the LBD. Influences
intracellular trafficking and subcellular distribution

16. (E) Ligand binding domain (LBD): Moderately
conserved in sequence and highly conserved in
structure between the various nuclear receptors.
(F) Cterminal domain: Highly variable in sequence
between various nuclear receptors

17. Molecular Structure NR

18. Mechanism of action
 Type I:
Bind to either a soluble receptor protein in either the
cytoplasm or inside the nucleus
Examples:
Sex hormone receptor
Cortisol receptor
Mineral corticoid receptor

19. Type I:

20. Mechanism of class I nuclear receptor action
A class I nuclear receptor (NR) , in the absence of
ligand , is located in the cytosol. Hormone binding to
the NR triggers dissociation of heat shock proteins
(HSP) , dimerization, and translocation to the nucleus,
where the NR binds to a specific sequence of DNA
known as a hormone response element (HRE) . The
nuclear receptor DNA complex in turn recruits other
proteins that are responsible for transcription of
downstream DNA into mRNA, which is eventually
translated into protein, which results in a change in
cell function.

21.  Type II:
Binds directly to DNA proteins
Examples:
Vitamin A
Vitamin D
Retinoid
Thyroid hormones

22. Mechanism of class II nuclear receptor action
A class II nuclear receptor (NR) ,regardless of ligand
binding status, is located in the nucleus bound to
DNA. For the purpose of illustration, the nuclear
receptor shown here is the thyroid hormone
receptor(TR) heterodimerized to the RXR. In the
absence of ligand, the TR is bound to corepressor
protein. Ligand binding to TR causes a dissociation of
corepressor and recruitment of coactivator protein,
which, in turn, recruits additional proteins such as
RNA polymerase that are responsible for transcription
of downstream DNA into RNA and eventually protein

23. Enzyme-linked receptors
 also known as a catalytic receptor
 transmembrane receptor, where the binding of
an extracellular ligand causes enzymatic activity on
the intracellular side
 integral membrane protein possessing both
enzymatic catalytic and receptor functions
 Upon ligand binding a conformational change is
transmitted which activates the enzyme, initiating
signaling cascades

25. 1. Receptor serine/threonine kinase
2.Receptor tyrosine kinases
3. Tyrosine kinase-associated receptors

26. 1. Receptor serine/threonine kinases
 There are two types of serine/threonine kinase
receptors, both of which contain an intracellular
kinase domain.
 They are each dimeric proteins, so an active receptor
complex is made up of four receptors

27. Type I receptors:
• Inactive unless in complex with type II receptors.
• Do not interact with ligand dimers.
• Contain conserved sequences of serine and threonine
residues near to their kinase domains.

28. Type II receptors:
• Constitutively active kinase domains (even in the
absence of the bound ligand).
• Able to phosphorylate and activate the type I receptor

31. 2. Receptor tyrosine kinases (RTKs)
 RTK ligands, such as fibroblast growth factor (FGF),
epidermal growth factor (EGF), nerve growth factor
(NGF) etc. bind as dimers.
• Ligand binding to RTK monomers results in dimer
formation.
• Receptors possess an intracellular tyrosine kinase
domain. Within the dimer the conformation is
changed, locking the kinase into an active state.

32.  The kinase of one receptor then phosphorylates a
tyrosine residue contained in the "activation lip"of
the second receptor.
• This forces the activation lip out of the kinase active
site, allowing ATP bind and resulting in enhanced
kinase activity.
• This induces phosphorylation at further tyrosine
residues.
• Phosphotyrosine is a conserved "docking site" for
many intracellular signal transduction proteins that
contain SH2 domains

34. 3. Tyrosine-kinase-associated
receptors
 Cytokines are the main ligands that signal through
tyrosine kinase-associated receptors.
• The intracellular side of each receptor is bound to a
cytosolic tyrosine kinase protein.
1. Cytokines bind simultaneously to two receptor
monomers.
2. This brings the two associated kinases closer
together.

35. 3. One kinase phosphorylates the other kinase in an
area called the "activation lip" (similar to RTK
activation).
The activation lip moves out of the active site and
binds ATP therefore enhancing kinase activity.
4. The enhanced kinase phosphorylates more tyrosine
residues on the intracellular portion of the receptor.
5. Phosphotyrosines serve as "docking sites" for SH2
domain-containing proteins