G-Protein-Coupled Receptor (GPCR): G-Protein-Coupled Receptor (GPCR): Structure and Function Structure and Function

Yun HuangYun Huang

The largest family of integral

membrane protein involved in

many biological process and p

athologies; 50% of all modern drugs and

25% of the top 200 best selling

drugs are estimated to target G

PCRs; Transduce the signals media

ted by diverse signaling molec

ules, such as ions, peptides,

lipids and photons, to induce di

fferent 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

G-Protein-Coupled Receptor (GPCR)G-Protein-Coupled Receptor (GPCR)

GPCR-GGPCR-Gαα Fusion Protein Fusion Protein

Nat Rev Drug Discov. 2004 Jul;3(7):575, 577-626. Review.

Upper: Schematic of a G-protei

n-coupled receptor (GPCR)-Gα fu

sion protein;

Left: G-protein cycling. Rate-lim

iting receptor-promoted GDP diss

ociation;

Three Families of GPCRThree Families of GPCR

Nat Rev Drug Discov. 2004 Jul;3(7):575, 577-626. Review.

Ligands: neurotranmitters (dopamine and serotonin)

Ligands: hormones (glucagon, secretin, PTH) Example: mGluR, CaR

Family 1 GPCRs: Rhodopsin-like ReceptorsFamily 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.

Rod cell specific visual pigment prot

ein found in the vertebrate retina Responsible for achromatic vision u

nder dim light conditions 348 amino acids, 7-TM, 11-cis-retin

aldehyde (chromophore, derived from

Vit A) Posttransliational modifications: ace

tylation (M1), N-Glycosylation (N2, N1

5), S-palmitoylation (C322, C323) Prosthetic group retinaldehyde moie

ty covalently attached to K296 Functions as oligomers (dimers?)

11

33

22

44

55 66

77

1U191U19

N

C

RhodopsinRhodopsin

Current Opinion inStructural Biology, 2005, 15:408-415; Experimental Eye Research, 2005, 81: 366-367

Visual Signal TransductionVisual Signal Transduction

http://www.biocarta.com/pathfiles/m_gpcrPathway.asp

Family 2 GPCRs: Secretin-like ReceptorsFamily 2 GPCRs: Secretin-like Receptors

15 peptide-binding receptors in human; Relatively long N-terminus (~100-160 residues) and a juxtamembrane doamin of 7 m

embrane-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.

Drug Discovery today, 2005: March;10(3):417-427. Review.

Family 2 GPCRs: Secretin-like ReceptorsFamily 2 GPCRs: Secretin-like Receptors

Corticotropin-Releasing Factor Receptor (CRF)Corticotropin-Releasing Factor Receptor (CRF)

PNAS, 2004;101: 12836-12841.

Related to human stress r

esponse; NMR structure of ECD1-C

RF-R2β; Clustered in the cleft regio

n between the tip of the first

β-sheet and the edge of the

“palm” of the second β-sheet;

The central core contains

a salt bridge sandwiched bet

ween aromatic side chains;

Binding Model of Family 2 GPCRsBinding Model of Family 2 GPCRs

Peptide interaction (two-domain model)

Non-peptide interaction

Drug Discovery today, 2005: March;10(3):417-427. Review.

Drug Discovery today, 2005: March;10(3):417-427. Review.

Comprise a central core: a “top” side chain and a

“bottom” aromatic ring; Developed by Janssen Pharmaceuticals NY & N

eurocrine Biosciences; Phase II clinical trials for treating depression and

anxiety

Drug Design Based on Protein StructureDrug Design Based on Protein Structure

Family 3 GPCRs: mGluR-like ReceptorsFamily 3 GPCRs: mGluR-like Receptors

Very long N-terminus; Ligand-binding domain is located in N-terminus and is thought to resemble a Ven

us 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 CaRStructure of mGluR and CaR

Glutamate is a neurotransmitter in CNS a

nd functions in long-term potentiation, learnin

g and memory; Metabotropic glutamate receptor (mGluR)

mediate excitatory transmission on the cellul

ar surface through initial binding of glutamate

Calcium sensing receptor (CaR) shares 2

7% sequence identity with (mGluR); Response to [Ca2+]o, L-amino acids, polya

mines, ionic strength and pH; Parathyroid CaR plays a central role in sy

stemic PTH level and Ca2+ homeostasis;

Nature 2006, 407: 971-977; Current Opinion in Neurobiology 2003, 13: 271-278

??

Structure of mGluR and CaRStructure of mGluR and CaR

mGluRmGluR

CaRCaR

Nature 2006, 407: 971-977; Current Opinion in Neurobiology 2003, 13: 271-278

Extracellular Calcium Sensing Receptor (CaR)Extracellular Calcium Sensing Receptor (CaR)

Cell calcium. 2004 35: 217-228. Review;

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;

http://www.casrdb.mcgill.ca/?Topic=CasrMutation

Familial hypocalciuric hy

percalcemia (FHH), Neonatal severe hyperpa

rathyroidism (NSHPT), Autosomal dominant hyp

oparathyroidism (ADH)

Disease Related Disease Related Natural-OccurrinNatural-Occurring Mutations on Cg Mutations on C

aRaR

Drug Design Based on Protein StructureDrug Design Based on Protein Structure

Calcimimetics: Mimic or potentiate the action of extracellular Ca2+ at the Ca2+ rec

eptor; 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 sBig questions remain for GPCRs at the structure/function interfacetructure/function interface

Determine the structures corresponding to the various

states of GPCRs, especially in the active state;

Understand how GPCRs interact with and activate het

erotrimeric 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.

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 G-pro

tein-coupled receptors. Drug Discov Today. 2005 Mar 15;10(6):417-27. NMR structure and peptide hormone binding site of the first extracellula

r 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 glut

amate receptor. Nature. 2000 Oct 26;407(6807):971-7. Extracellular Ca2+-sensing receptors--an overview. Cell Calcium. 2004

Mar;35(3):183-96.

ReferenceReference