g-protein couple receptor genetic variation in gpcr

1. GENETIC VARIATION IN GPCR
SUBJECT NAME:- cellular and molecular pharmacology
Topic:- genetic variation in G protein coupled receptors
SUBMITTED BY:-
GUIDED BY:-
Nittal vekaria (roll no:48)
Mumuxa Rathod
M.pharm pharmacology(sem 1)
[kbiper]

2. WHAT IS G-PROTEIN?
• Also known as guanine nucleotide binding proteins.
• Family of protein that act as a molecule switches inside the cell.
• Activity regulated by factors that controls their ability to bind to and
hydrolyse GTP into GDP.
• When they are bound to GTP they are "on" and when they are bound to
GDP, they are "off ".
• G - protein belong to the larger group of enzyme call GTPase.
• There are two classes of G proteins :
a) monomeric small GTPase
b)heterotrimeric g protein complex's ( alpha, beta, gamma subunit)

3. Gq & Gs :- stimulatory
Gi :- inhibitory
RhoGEF :- rho guanine nucleotide
exchange factor
PIP2 :- Phosphatidylinositol 4,5-
bisphosphate
DAG:- Diacylglycerol
IP3 :- phosphatidylinositol (3,4,5)-
trisphosphate

4. G- PROTEIN COUPLED RECEPTOR
• 7 trans membrane helices connected by altering cytosolic and extra
cellular loop.
• C- terminal:- inside the cell
• N- terminal:- extracellular portion
• Extra cellular portion has unique messenger binding site.
• Cystolic loop allow receptor to interact with G protein.

6. GPCR comprise the largest membrane receptor superfamily and are the
most commonly used therapeutic targets. GPCR genetic numerous
variants, such as DNA insertions or deletions and single nucleotide
polymorphisms that alter GPCR expression and function, thereby
contributing to inter-individual differences in disease
susceptibility/progression and drug responses.

7. CAUSES FOR VARIATION IN GPCR
=]> Sequence variations of the human genome
=]> Structure & function of GPCRs
=]> GPCR coupling to G proteins and other signaling pathways
=]> GPCR binding pockets
=]> Spontaneous GPCR signalling
=]> Multiple receptor conformations with distinct functions

8. 1. Sequence variation of human genome:
• Introduction variability in genetic make up.
• Suspected to play a main role in diseases and variable response in drug
therapy.
• Polymorphism :- refers to sequence variation leading to occurrence of
two or more clearly different forms.
• Single nucleotide polymorphism accounts for approx. 80% of all
sequence variations.

9. 2. STRUCTURE AND FUNCTION OF GPCRs
• Comprises a large class of membrane proteins encoded by approx ,600
human genes.
• Molecular architecture might permit the prediction of functionally
relevant domains where sequence variations are more likely to alter
receptor function.
• Normally, tm domains are highly conserved the loop are variable in
sequence & length & the -c and -n terminal tails represents the most
diverse elements.

10. 3.GPCR COUPLING TO G PROTEINS AND OTHER
SIGNALLING PATHWAYS
• GPCR thought to be couple to heterotrimeric G protein composed of
alpha, beta and gamma subunits. It display considerable heterogenicity,
with a predicted number of 27 different alpha , 5 beta and 13 gamma
subunits.
• Mains sites of contact between receptor g protein include the 3rd
intracellular loop But IL1,IL2 and the -c terminal have also been
reported to contribute g protein coupling.
• Proteins like protein kinases, arestin and phosphatases modulates
receptor functions at distinct domains that are possible targets for
polymorphic effects.

11. 4. GPCR BINDING POCKETS
• Ca++, acetyl choline, glutamate, bradykinin, prostaglandins & the large
polypeptide FSH bind to same site.
• Distinct binding sites appear to exist, either embedded within the pocket
formed by the 7 - tmd bundle within the membrane , at pockets formed by
the extracellular loops or in the n terminus.
• The thrombin receptor family represent a special case whereas the protease
activity of the ligands thrombin cleaves a portion of the n terminus. The
newly generated N terminus then serves as a tethered ligand.

12. 5. SPONTANEOUS GPCR SIGNALLING
• Exchange of single amino acid residues can lead to constitutive
receptor activation.
• considerable number of human polymorphisms enhance
signalling(gain of function) or even activation the receptor
constitutively, causing serious genetic disorder.

13. 6. MULTIPLE RECEPTOR CONFORMATIONS WITH
DISTINCT FUNCTION
• GPCR are flexible structures and may accommodate ligands in
various ways. It exists in multiple conformations.
• discrete signalling pathways are triggered by discrete conformational
states of GPCR.

14. SEQUENCE VARIATION OF GPCRS AND
ASSOCIATED DISEASE

16. IMPAIRED OR ENHANCED AGONIST SIGNALLING
EFFICACY
Several inactivating sequence variants of peptide receptors have been
associated with congenital disorders. For example,
1. A point mutation causing truncation of thyrotropin stimulating
hormone(TSH) receptor leads to Leydig's cell hyperplasia.(Activating
mutation)
truncated TM5, D578G, T398M
2. Inactivating mutations of the ACTH receptors are associated with
familial glucocorticoid deficiency. The mutation occurs in the large N-
terminus, the binding site for glycoprotein hormone receptor, leading to
toxic multinodular goitre.
S120R, R201STOP, S74I, V254C

17. V2 VASOPRESSIN RECEPTORS
A number of mutations in the gene
coding the V2 vasopressin receptors
leads to functionally inactive
receptor protein and are causative
for nephrogenic diabetes
insipidus.(Missense mutations).
This is clear indication that receptor
activity depends on intact signalling
pathways. (Multiple snps; decreased
ligand binding: R113W; R137H)

18. THROMBOXANE A2 RECEPTOR
• This receptor performs an essential role
in haemostasis by include platelet
aggregation. An R60L amino acid
substitution in the first cytoplasmic loop
of TBXA2 receptor.
• causes a dominantly inherited bleeding
disorder characterised by defective
platelet response to TBXA2. This leads to
decreased agonist-induced second
messenger formation.

19. P2Y12 ADP RECEPTOR
• This receptor sub- type is shown to
be the target for anti-thrombotic
drugs such as ticlodipine &
clopidogrel. 2-nucleotide deletion in
a region mapping to the end of
TMD6, associated with a rare
bleeding disorder.

20. CHEMOKINE RECEPTOR
• Fusin and CKR5 have been identified as a co-receptor for the cellular entry
of HIV. Similarly, certain chemokines were found to block HIV entry into
cells.
• Natural resistance can be either by high endogenous levels of chemokines
or by mutations of the receptors.
• A 32 bp deletion in CCR5 leading to a frame shift and a non functional
protein appeared to protect homozygous carriers against hiv infection and
blocking its entry.
• Val 64 substitution with Ile was shown to result in heterodimerisation of
CCR2 with CCR5 or CXCR4, thereby promoting resistance to aids.

21. BIOGENIC AMINE RECEPTOR
• The R16G substitution in the beta 2 adrenoreceptors has been
associated with nocturnal asthma whereas W64R in the beta 3 receptor
expressed in adipocytes are involved in energy metabolism is linked
with obesity.

27. References :-
• John Dickenson, molecular pharmacology, published by wiley
Blackwell.
• Sela, G. Golan, M. StrajbI, meenakshi gupta, G-protein couple
receptor 2017.
• D. Rivenzon-segal, S.Bar-Haim, I Bloch, B. Inbal, A. Sahitrit, E. Ben-
Zeev, M. Fithman, Y. Markus, H. Senderowitz, O. Kales. Genetic
variations of g-protein couple receptor. Current Topics in Medicinal
Chemistry, 2010.
• https://www.researchgate.net/publication/225767417