G PROTEIN COUPLED RECEPTORS

MANJU K M MSC PLANT SCIENCE

• Guanosine nucleotide binding protein• Serpentine receptor• 7 transmembrane protein

• Ligand binding causes a change in receptor conformation that activate a particular

G Protein• A portion of activated G protein binds to a

target protein there by altering targets activity• Eg: Olfactory receptors Norepinephrine receptors Hormone receptors

G-protein-coupled receptors (7-TM receptors) Structure - Single protein with 7 transmembrane regions

Transmembranehelix

C-Terminal chain

G-Proteinbinding region

Variableintracellular loop

Extracellularloops

Intracellular loops

N-Terminal chain

HO2C

NH2

VII VI V IV III II IMembrane

Structure of G protein

7 transmembrane helices connected by alternating cytosolic and extra cellular loop

C terminal: inside the cellN terminal : extra cellular regionExtra cellular portion has unique messenger

binding siteCytosolic loop allow receptor to interact with G

protein

G protein contain 3different subunitsG AlphaG BetaG Gamma

G alpha – largest , binds to GTP or GDPG beta & G gamma permanently bound together

Act like MOLECULAR SWITCHESON – when bind to GTPOFF – when bind to GDPWhen G alpha bind to GTP it detaches from beta and gamma complex

• When a messenger bind to GPCR the receptor change its conformation

• G alpha releases its bound GDP and acquires a new molecule of GTP

• G alpha detaches from G beta & G gamma complex

• Either the GTP-G alpha subunit or G beta gamma can initiate signal transduction

Activity of G Protein persists as long as• GTP is bound to G alpha subunit • G alpha and g beta –g gamma complex remain

separated This feature allows the signal transduction

pathway to shutdown when the messenger is utilized

• RGS –Regulators of G Protein signaling Protein

Cyclic AMP production is regulated by G protein

CALCIUM ION RELEASING & GPCR

• The beta & gamma subunits can also trnsduce signals

• Eg: muscarinic acetylcholine receptors

Nobel prize for chemistry 2012 for studies of GPCR

ROBERT J. LEFKOWITZ BRIAN K . KOBILKA

THANK YOU