G-proteins are proteins that act as molecular switches inside cells and are involved in signal transduction. They have two classes: monomeric small GTPases and heterotrimeric G-protein complexes composed of alpha, beta, and gamma subunits. G-protein coupled receptors (GPCRs) have 7 transmembrane domains and interact with G-proteins via intracellular loops to regulate their activity. Genetic variations in GPCRs and associated proteins can lead to diseases by altering receptor function, such as impaired or enhanced signaling. Single nucleotide polymorphisms in receptors like beta-adrenergic and chemokine receptors have been linked to conditions like asthma and HIV resistance.

1. ANANYA UPADHYAY
M.PHARM (PHARMACOLOGY)

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. 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 has
• Extra cellular portion has unique messenger binding site .
• Cystolic loop allow receptor to interact with G protein .

5. GENETIC VARIATION MAY BE
DUE TO
1. Sequencevariationof humangenome:-
• 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.

6. .
2. STRUCTUREANDFUNCTIONOF 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.

7. 3. GPCRCOUPLINGTO G PROTEINS ANDOTHERSIGNALLINGPATHWAYS
• 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 i1,i2 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.

8. 4. GPCRBINDINGPOCKETS
• 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.

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

10. SEQUENCE VARIATION OF GPCRS AND
ASSOCIATED DISEASE

11. IMPAIREDOR ENHANCEDAGONIST SIGNALLINGEFFICACY
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 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

12. V2 VASOPRESSINRECEPTORS
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)

13. 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.

14. P2Y 12ADP
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.

15. 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 ckr5 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 lle was shown to result in heterodimerisation of ccr2 with ccr5 or cxcr4,
thereby promoting resistance to aids.

16. BIOGENICAMINE 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.

17. B1 ADRENGRIC RECEPTOR:- SINGLE NUCLEOTIDE POLYMORPHISM
• B1 ARS expressed in heart . Increase in heart rate and contractility in response to endogenous
catecholamine nor adrenaline and adrenaline.
• B1ARS SNPs is B1AR antagonist . 2 major non synonymous SNPs have identified with coding
region of B1AR.

18. B2AR SNPS ANDASTHMA
• B2Ar agonists are widely used as bronchodilators in treatment of asthma and their clinical
response marks individual variation .
• B2AR agonist are divided in 2 types short acting and long acting .
• Long acting B2 agonist Salmeterol lasts for 12 hours and short acting last between 4-6 hours .
• Long acting B2AR agonist are prescribe in conjugation with corticosteroids .

19. REFERENCE :-
John Dickenson, Molecular Pharmacology, Published by Wiley Blackwell.

20. THANK YOU