WHAT A LADD Flashcards
(1) Structure of GPCRs
- 7 transmembrane domains
- Exoplasmic N-terminal binds ligand
- Cytoplasmic loop 3 interacts with G protein
- Cytoplasmic C-terminal tail involved in regulating GPCR
(1) 3 main mammalian GPCR subfamilies
A: Rhodopsin-like group (most of GPCRs)
B: Secretin receptor family
C: Venus fly trap: Metabotropic gluatmate and GABAa receptor family
(1) VAS IS DAS Orphan receptors
GPCRs that are identified which family they are in by homology cloning but unknown activating ligand
(1) What are RGS
Regulators of G protein signalling
(1) G proteins and 2nd messenger
Gs = mediated by alpha (adenylyl cyclase + Ca2+ channels) Gi = alpha = inhibits adenylyl cyclase Gq = alpha = activates phospholipase C-B
(1) G-protein cycle thingy
1) Resting (GDP-bound) state
2) Ligand binding and nucleotide exchange in Ga (GDP to GTP)
3) Active (GTP-bound state)
Ga dissociates and binds effector
GB and Gy bind other effector (Internal signalling occurs
4) GTPase activates
RGS binds Ga (GTP to GDP)
5) Ligand dissocaition, G-protein timer formation
(1) Common experimental tools used to study GPCRs
1) Cholera toxin
-Causes ADP ribsoylation of Gas
-Prevents GTP hydrolysis
-ALWAYS activating adenylate cyclase
-Lots of cAMP
DEATH
2) Pertussis Toxin (PTX)
- Causes ADP ribosylation of Gai
- Prevents release of GDP. INACTIVE
- Prevents inhibition of adenylate cyclase
- Same as cholera
(1) RGS proteins function
Negative regulators of G protein signalling
-Enhance Ga proteins intrinsic GTPase activity
(1) Regulation of GPCR function
1) De/resensitisation: Decrease in responsivness during continous drug application (right-shift in drug dose response curve)
- Long term desense: Changes in G protein levels, mRNA expression
- Rapid desense: Receptor phos, arrestin binding, receptor internalisation
(1) 2 types of densensitisation
Heterologous desense: 2nd messneger kinase (PKA/PKC) = Then arrestin bindig
Homologous desense: G-protein coupled receptor kinase (GRK)
B-arresting binding to phos GPCR is required to decrease GTPase activity prior to densense
(1) Arrestin mechanisms
- Promotes uncoupling of G protein
- Desense by binding to clathrin and calthrin adaptor protein AP2
- Promotes G-protein independent signalling
(1) GPCR heterodimers
Family C GPCRs
ALSO Rhodopsin homodimers
(e.g. Vasopressin and OT Rs)
(1) VAS IS DAS Orthosteric site
The site where agonists and antagonists bind to on a GPCRs
PAM: Positive allosteric modulator
NAM: Negative allosteric modulator
(1) VAS IS DAS Signal bias
GPCRs have a preference and higher affinity for certain ligands over other and produce a greater response to them.
(2) Diabetes
A metabolic disorder of multiple aetiology characterised by chronic hyperglyceamia with disturbances of carbohydrate, fat and protein metabolism resulting from defects in insulin secretion or action or both.