Transcript G-Protein-Coupled Receptor (GPCR)

G-Protein-Coupled Receptor (GPCR):
Structure and Function
Yun Huang
G-Protein-Coupled Receptor (GPCR)
 The largest family of integral
membrane protein involved in
many biological process and
pathologies;
 50% of all modern drugs and
25% of the top 200 best selling
drugs are estimated to target
GPCRs;
 Transduce the signals
mediated by diverse signaling
molecules, such as ions,
peptides, lipids and photons, to
induce different intracelluar
function;
 Bind their ligand and to
activate different G proteins;
http://www.sigmaaldrich.com/Area_of_Interest/Life_Science/Cell_Signaling/Scientific_Resources/Pathway_Slides___Charts.html
GPCR-Gα Fusion Protein
 Upper: Schematic of a G-
protein-coupled receptor (GPCR)Gα fusion protein;
 Left: G-protein cycling. Rate-
limiting receptor-promoted GDP
dissociation;
Nat Rev Drug Discov. 2004 Jul;3(7):575, 577-626. Review.
Three Families of GPCR
Ligands: neurotranmitters (dopamine and serotonin)
Ligands: hormones (glucagon, secretin, PTH)
Example: mGluR, CaR
Nat Rev Drug Discov. 2004 Jul;3(7):575, 577-626. Review.
Family 1 GPCRs: Rhodopsin-like Receptors
 Represent the predominant class of GPCRs;
 Several highly conserved amino acid (red circles);
 Disulfide bridge between first and second extracellular loops (ECLs), palmitoylated
cys in C-tail;
 The binding of small molecule ligands occures within the TM region;
 Example: Rhodopsin, Dopamine receptor, Chemokine receptors;
Nat Rev Drug Discov. 2004 Jul;3(7):575, 577-626. Review.
Rhodopsin
 Rod cell specific visual pigment
N
3
4
5
6
1
2
7
C
protein found in the vertebrate retina
 Responsible for achromatic vision
under dim light conditions
 348 amino acids, 7-TM, 11-cisretinaldehyde (chromophore, derived
from Vit A)
 Posttransliational modifications:
acetylation (M1), N-Glycosylation (N2,
N15), S-palmitoylation (C322, C323)
 Prosthetic group retinaldehyde
moiety covalently attached to K296
 Functions as oligomers (dimers?)
1U19
Current Opinion inStructural Biology, 2005, 15:408-415; Experimental Eye Research, 2005, 81: 366-367
Visual Signal Transduction
http://www.biocarta.com/pathfiles/m_gpcrPathway.asp
Family 2 GPCRs: Secretin-like Receptors
 15 peptide-binding receptors in human;
 Relatively long N-terminus (~100-160 residues) and a juxtamembrane doamin of 7
membrane-spanning α-helices (J-domain);
 Tertiary structure is stabilized by 3 disulfide bonds within 6 highly conserved Cys
 Share little sequence homology with family 1 and 3 GPCRs;
 Example: Corticotropin-releasing factor receptor, Glucagon receptor, PTH receptor;
Nat Rev Drug Discov. 2004 Jul;3(7):575, 577-626. Review.
Family 2 GPCRs: Secretin-like Receptors
Drug Discovery today, 2005: March;10(3):417-427. Review.
Corticotropin-Releasing Factor Receptor (CRF)
 Related to human stress
response;
 NMR structure of ECD1CRF-R2β;
 Clustered in the cleft
region between the tip of the
first β-sheet and the edge of
the “palm” of the second βsheet;
 The central core contains
a salt bridge sandwiched
between aromatic side
chains;
PNAS, 2004;101: 12836-12841.
Binding Model of Family 2 GPCRs
Peptide interaction (two-domain model)
Non-peptide interaction
Drug Discovery today, 2005: March;10(3):417-427. Review.
Drug Design Based on Protein Structure
 Comprise a central core: a “top” side chain and a
“bottom” aromatic ring;
 Developed by Janssen Pharmaceuticals NY &
Neurocrine Biosciences;
 Phase II clinical trials for treating depression and
anxiety
Drug Discovery today, 2005: March;10(3):417-427. Review.
Family 3 GPCRs: mGluR-like Receptors
 Very long N-terminus;
 Ligand-binding domain is located in N-terminus and is thought to resemble a
Venus fly trap (VFT) that can open and close with the agonist bound inside;
 Cys residues are conserved, the tertiary structures are likely highly conserved;
 Share similar ligands and downstream signaling pathway;
 Constitutive homo- or heterodimers: mGluR (homo), GAGAβ(hetero);
 Example: metabotropic glutamate receptor (mGluR), CaR, GABAβ
Nat Rev Drug Discov. 2004 Jul;3(7):575, 577-626. Review.
Structure of mGluR and CaR
 Glutamate is a neurotransmitter in CNS
and functions in long-term potentiation,
learning and memory;
 Metabotropic glutamate receptor (mGluR)
mediate excitatory transmission on the
cellular surface through initial binding of
glutamate
 Calcium sensing receptor (CaR) shares
27% sequence identity with (mGluR);
 Response to [Ca2+]o, L-amino acids,
polyamines, ionic strength and pH;
 Parathyroid CaR plays a central role in
systemic PTH level and Ca2+ homeostasis;
Nature 2006, 407: 971-977; Current Opinion in Neurobiology 2003, 13: 271-278
Structure of mGluR and CaR
mGluR
CaR
?
Nature 2006, 407: 971-977; Current Opinion in Neurobiology 2003, 13: 271-278
Extracellular Calcium Sensing Receptor (CaR)
CaR related signaling pathway
PTH: key endocrine factor in systemic Ca2+ homeostasis and involve moving
Ca2+ between bone and blood; Stimulate net bone loss or formation;
Cell calcium. 2004 35: 217-228. Review;
Disease Related
NaturalOccurring
Mutations on
CaR
Familial hypocalciuric
hypercalcemia (FHH),
 Neonatal severe
hyperparathyroidism
(NSHPT),
 Autosomal dominant
hypoparathyroidism (ADH)

http://www.casrdb.mcgill.ca/?Topic=CasrMutation
Drug Design Based on Protein Structure

Calcimimetics:
 Mimic or potentiate the action of extracellular Ca2+ at the Ca2+
receptor;
 Agonists or allosteric activators of the receptor;

Calcilytics:
 Ca2+ receptor antagonists;
Selective and does not affect the
activity of mGluRs;
Increase [Ca2+]i and inhibits PTH
secretion;
Treatment of HPTH;
Drug Discovery today, 2005: March;10(3):417-427. Review.
Big questions remain for GPCRs at the
structure/function interface

Determine the structures corresponding to the various
states of GPCRs, especially in the active state;

Understand how GPCRs interact with and activate
heterotrimeric G proteins;

Gain a molecular understanding of the mechanism of
action of allosteric modulators, therefore, leads for drug
development;
Nat Rev Drug Discov. 2004 Jul;3(7):575, 577-626. Review.
Reference
 The state of GPCR research in 2004. Nat Rev Drug Discov. 2004
Jul;3(7):575, 577-626.
 Structure of rhodopsin and the metarhodopsin I photointermediate.
Curr Opin Struct Biol. 2005 Aug;15(4):408-15.
 Mechanisms of peptide and nonpeptide ligand binding to Class B Gprotein-coupled receptors. Drug Discov Today. 2005 Mar 15;10(6):417-27.
 NMR structure and peptide hormone binding site of the first
extracellular domain of a type B1 G protein-coupled receptor. Proc Natl
Acad Sci U S A. 2004 Aug 31;101(35):12836-41.
 Structural basis of glutamate recognition by a dimeric metabotropic
glutamate receptor. Nature. 2000 Oct 26;407(6807):971-7.
 Extracellular Ca2+-sensing receptors--an overview. Cell Calcium. 2004
Mar;35(3):183-96.