disorders associated with gprs
DESCRIPTION
Disorders Associated with GPRs. Members: 王建博、秦涛、李中印、王宇. The structural and signal transmit mechanism of the class-C G-protein-coupled receptors. First. What is this? One of the five classes GPCRs How does the GPCRs classified? Based on sequence similarity. - PowerPoint PPT PresentationTRANSCRIPT
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LOGO
Disorders Associated with GPRsMembers:王建博、秦涛、李中印、王宇
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The structural and signal transmit mechanism of the class-
C G-protein-coupled receptors
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First
What is this? One of the five classes GPCRs
How does the GPCRs classified? Based on sequence similarity. class-A:Rhodopsin( 视紫红质 )-like receptors class-B:secretin( 分泌素 )-like receptors class-C:mGlu-like receptors
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What are class-C GPCRs include? neurotransmitters receptors glutamate( 谷氨酸盐 ) receptors GABA receptors the calcium-sensing receptor sweet taste receptors pheromone( 信息素 )receptors
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Difference
A large extracellular domain——VFTVFT : Venus Flytrap (bilobate 双叶形 )
Can be regulared by allosteric modulator (变构调节剂)
Dimer ——homo or heter
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The structural
Four parts1.VFT(Venus Flytrap): the agonist
binding site2.CRD(cysteine-rich domain)3.HD(heptahelical domain) C-term
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VFT
Tow parts:Lobe-I&Lobe-II
Two conformations : Open(inactive) & Closed(active)
antagonist & agonist ( 抑制剂 ) ( 激动剂 )
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Lobe-I
Lobe-II
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CRD
The structure and function are unknown
absent CRD:GABA receptor
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HD ( Heptahelical domain )
Heptahelical
long C-terminal tail
Activity site positive & negative allosteric modulators
independency
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How is the signal transduced from one domain to the other?
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Homodimeric receptors mGlu receptor
A disulfide-linked dimer Cys-residues
Class-C GPCRs are constitutive dimers
Lobe-I
Lobe-II
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Heterodimeric receptors GABAB receptor
Absent disulfide bridge no covalent( 共价的 ) linkage
May have interaction between intracellular tail
ER retention signal (GABAB1)
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Activation mechanism of class-C GPCRs
interaction between the VFTs
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www.themegallery.comLOGO
On mGlus receptor
(Roo, resting-open-open) (Aco, active-closed-open) (Acc, active-closed-closed)
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Are both Aco & Acc conformations lead to similar properties?
Mutated mGlu VFT composed of two distinct binding sites
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Roo, none activity Aco, half activity Acc, full activity(Ca2+)
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Why?Roo state: This interface revealed major charge
repulsion
Aco state: the interface consists of a number of
ionic interactions
Acc state: four acidic side chains are facing each
other, creating a cationbinding site
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Only have two conformations A signal agonist can fully activate a
receptor
Surprisingly GABAB receptor in which GABA binds
in the GABAB1 VFT only
On GABAB receptor
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But
GABAB2 is necessary for GABAB
only those possessing both the GABAB1 and GABAB2 VFTs display agonist-induced activity
Why Unknown
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Allosteric coupling between the extracellular and HD within the
dimer
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On GABAB receptor
HD of GABAB2 is a important part
Experiment IMutations into either the i2 or i3 loop
of GABAB2 suppressed G-protein activation.
The equivalent mutation in GABAB1 had a minor effect
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Experiment II
GABAB1
VFTGABAB2
VFT
GABAB2 HD GABAB2 HD
Demonstrating that the HD of GABAB2 possesses enough of the molecular determinants required for G-protein coupling
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GABAB2 HD expressed alone can be activated by CGP7930, a positive allosteric modulator of the GABAB receptor.
So.. trans-activation occurs in the GABAB
receptor
Experiment III
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Another Experiment
GABAB1 VFT +GABAB2 HD =can not be activated
(GABAB1 VFT + GABAB2 HD) +(GABAB2 VFT + GABAB1 HD)
= can be activated
In this combination subunits cis-activation occurs
GABAB1
VFT
GABAB2 HD
GABAB2
VFT
GABAB1 HD
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In a word, dimer conformation takes a very important part in GABAB receptors
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On mGlu receptor
Both cis- and trans-activation occur in mGlu receptors
Because the homodimeric structure
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Allosteric functioning of the HD of class C GPCRs
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HD can exist in three states
HDg states:totally inactive state
HD states:Low active efficiency state
HD* states:High active efficiency state
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HD can be regulared by positive & negative allosteric modulators ( 变构调节剂 )
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Allosteric modulators are compounds able to regulate
the activity of a receptor by binding at a site distinct from that where endogenous ligands bind
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Classification negative allosteric modulators inhibit constitutive activity of the receptor
positive allosteric modulators activate the receptor , can enhance either the
potency (力量) or the efficacy (效力) , or both
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DifferenceNegative ——directlyPositive——indirectly(with agonist)
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SO…
the action of negative allosteric modulators is less dependent on the concentration of endogenous ligand(agonist)
But positive allosteric modulators is highly dependent on agonist
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Experiment
Bay 7620:negative allosteric modulators Ro01-6128: positive allosteric modulators
EC50 :value of glutamate
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Why we intrested in allosteric modulators?
Both positive & negative modulators are highly receptor subtype selective.
less side effect , long effect Hydrophobic, allowing them to cross the
blood brain barrier more easily