GPCRs Flashcards
What are the 3 superfamilies of transmembrane receptors?
ligand-gated ion channels
GPCRs
Kinase-linked receptors
What are the 5 main Human GPCR families and some of their features?
Adhesion - look like adhesions but don’t act as such
Secretin - sm. amino terminus
Glutamate - extracellular binds to ligands
Frizzled/TAS2 - Wnt receptors control cell fate, proliferation
Rhodopsin - large group with alpha, beta, gamma and delta
What do the a, b and delta relate to in the rhodopsin family?
a - prostaglandins, dopamine, muscarinic receptors, opsin
b - peptide receptors
delta - olfactory receptors
How can GPCR chimeras be used to identify their functional regions? Give examples
with a FSH extracellular region and a LH intracellular region the expressed signalling pathway is LH.
the transmembrane domain is not important, it is the 3rd intracellular loop onwards which determines its interaction with the G-Protein
What are the subunits involved in a G Protein?
a, b, gamma
How is GDP exchanged for a GTP?
the active receptor acts as a guanine nucleotide exchange factor stimulating the exchange of GDP in the a-subunit and allowing a subunit dissociation from the beta-gamma subunit
How does GTP activate the G-Protein?
within the G-protein a short loop is held on the surface, which interacts with the terminal phosphate on the GTP. This causes subunit dissociation. When GDP is there, the phosphate cannot interact with the loop allowing the subunits to associate
How does GTP hydrolysis occur?
by nucleophilic attack by a water molecule
How is switch domain II involved in GTP hydrolysis?
it contains a conserved glutamine molecule which positions the attacking water molecule next to the GTP active site
How does the b-subunit help provide a stable support unit for the a-GDP subunit?
it has a WD repeat sequence that binds Ga in the GDP bound form
Why is Mg usually an essential co-factor for GTPase activity?
It helps form salt bridges as the +Mg and -PO group allowing the phosphate to be cleaved
Cholera toxin can render this useless
What are the G Protein families and their associated actions?
Gs - B adrenoceptors/olfactory - increase AC
Gi - a2 adrenoceptors/5HT/taste - decrease AC/cAMP
Gq - a1 adrenoceptors/5HT2 - increase PLC
What are the key players in the signalling cascade and their function?
AC - adenylyl cyclase - enzyme creating cAMP
cAMP - signal modulator for other molecules such as PKA
RGS - inhibits the Ga and therefore the signalling mechanism
PDE - breaks down cAMP
CREB - makes changes to gene expression from PKA signalling
What are the four components of AC?
receptors for hormones that regulate cAMP synthesis
regulatory G proteins
Adenylyl cyclises responsible for synthesis of cAMP
PDE enzymes responsible for cAMP hydrolysis
What does cAMP interact with?
PKA
Epac
cyclic gated nucleic ion channels
