Theresa Filtz, PhD
Phar 735, Winter 2005
G protein-coupled Signal Transduction
Main Objectives (the big chunks)
•Describe in molecular detail the cascades of events in a generalized G protein-coupled signaling pathway
函授是什么意思•Describe the structure of a GPCR and how it relates to function
•List the four major class of G a subunits and the effects of toxins on their activity
•List the major, proximal cond mesngers produced by adenylyl cycla and PLC-b
•Describe GPCR densitization and supernsitization and discuss the conquences for drug action
topspeed
•Compare the effects of changing cyclic AMP and calcium levels in cardiac cells and in smooth muscle cells
G protein coupled receptors (GPCR)organic food
•Function
The receptor subtype mediating the actions
of hundreds to thousands of
endogenous and exogenous substances
Couple to a guanine nucleotide binding
protein (G protein)
G proteins activate effectors to initiate
signaling cascades
广州烘焙培训•Examples of drug acting through GPCRs
Bronchodilators-albuterol (Ventolin®, etc) Stimulants- Ritalin®, ephedra
Decongestants-Sudafed®
Antipsychotics-haloperidol, Zyprexa®, Geodon®Antihistamines-Benadryl®, Claritin®, Allegra®Pain medication-morphine and opioid analgesics Labor inducing agents-pitocin
Anti-hypertensives-b-blockers
Cardiac stimulants -atropine, dopamine, epinephrine, adenosine Epinephrine for vere allergic reaction
•Structure
One of the most abundant protein
families
At least a thousand different genes for GPCR in the human genome
Potentially a unique GPCR for every
dectectable odor
梦想dream
Seven transmembrane a helices
External NH 2 terminus and internal C tail
Binding pocket
Inside the a helices for small molecules and at the NH 2 terminus for larger peptides Intracellular loops
gripperBinding of activators to a helices affects configuration of the intracellular loops 2nd and 3rd loops and C tail interact with G proteins
Guanine nucleotide binding proteins (G Proteins)
• Structure and Function
Turn on effector enzymes
Heterotrimer--compod of three protein subunits—G a , G b , and G g
Other families of G proteins exist which rve other intracellular functions Bound by lipid chains to the intracellular surface of the plasma membrane G a subunit
Binds GDP and associates with G bg in the resting state Binds GTP and dissociates from G bg in the active state
Upon activation by receptor, releas GDP and picks up GTP Dissociates from G bg upon binding GTP
Activates effector enzymes when bound to GTP Intrinsic GTPa activity
Self-Hydrolyzes GTP back to GDP
Rejoins with G bg when bound to GDP to turn itlf off G bg subunit雅思口语练习网站
Exists mainly as a non-dissociable dimer Active when dissociated from G a subunit
Activates different effector enzymes when parated from G a Inactivated by binding G
a
•Subtypes
G a subtypes
Four major families, multiple subtypes
G a s
nuclear waste
Predominantly activates adenylyl cycla
Constitutively activated by cholera toxin
G olf olfactory G a subunit, activates ion channels in nasal epithelia
G a i
Inhibited by pertussis toxin
Predominantly inhibits adenylyl cycla
G a t, tranducin-the retinal light transduction subunit
activates cyclic GMP phosphodiestera in respon to light
G a o
inhibits some types of Ca++ channels
G a12,13
Involvement with growth regulatory pathways still being experimentally confirmed
G a q
Activates phospholipa C-b enzymes
G bg subtypes
Multiple subtypes of each subunit
Activate many enzymes including phospholipa C-b, cation channels, GPCR kinas,
subtypes of adenylyl cycla, among other signaling proteins
Which combination of subtypes activate which effectors is still being investigated
Effector enzymes
•Phospholipa C-b
library的音标Activated by G a q subunits OR G bg subunits (depending on isoform)
Hydrolyzes a low abundance membrane phospholipid, PIP2 (phosphatidylinositol 4,5-bisphosphate) into two products, IP3 (inositol trisphosphate) and DAG (diacylglycerol)
IP3
IP3 is water soluble and diffus through the cytoplasm to bind to receptors on the endoplasmic reticulum (ER)
IP3 receptor activation releas Ca++ from the ER into cell cytosol
Cells are exquisitely nsitive to changes in cytosolic Ca++ concentration
Ca++ activates Ca++/calmodulin-dependent kinas (CaM kinas)
CaM kinas activate multiple phosphorylation cascades
Lithium carbonate inhibits inositol recycling back into PIP2, causing a build-up of IP3 and
depletion of PIP2
DAG
Membrane bound lipid
Activates protein kina C (PKC)
PKC initiates multiple phosphorylation cascades
Phorbol esters are tumor promoters that mimic DAG and activate PKC
Activation of PLC-b leads to many physiologic respons including smooth muscle contraction, learning and memory, and cell growth and differentiation
•
GPCR = G protein coupled receptor PKC = protein kina C
PLC-b = phospholipa C-b
CaM = calmodulin
Adenylyl Cycla
Activated by G a s subunits Inhibited by G a i subunits Transforms ATP into cyclic AMP
cyclic AMP
Increas and decreas in cyclic AMP levels lead to different effects Activates cyclic AMP-dependent protein kina (PKA)Hydrolyzed by phosphodiesteras (PDE)
PDE is inhibited by theophylline (bronchodilator), caffeine, sildenafil (Viagra®), etc Involved in the classic glycogen metabolism pathway to liberate gluco for energy
PKA phosphorylates glycogen syntheta to inhibits activity PKA activates phosphoryla kina
phosphoryla kina converts glycogen phosphoryla b to glycogen phosphoryla a glycogen phosphoryla a promotes glycogen metabolism cyclic AMP also activates transcription factors
cyclic AMP respon element binding protein (CREB)
G a s
Adenylyl Cycla
G b g
PKA
GPCR
P P P
Stimulatory Hormone GPCR = G protein coupled receptor
PKA = cyclic AMP regulated protein kina PDE = phosphodiestera
G a i
anaesthesia
G b g
GPCR
Inhibitory Hormone +
-
ATP cyclic
AMP
AMP
PDE
