Signal Transduction II Flashcards
What does an agonist do?
It mimics the physiological ligand- it turns on a receptor
Synonyms for GCPR
heptahelical, serpentine (due to topography in the membrane)
How many transmembrane segments do GCPR have?
7 (sit as a helical bundle)
What sits down in the middle of a GCPR bundle?
catacholamine
G proteins that interact with GCPR are of what conformation?
triheteromeric
What does triheteromeric mean?
Three subunits that are not identical (a, B, y)
In the basal state, what is bound to the a subunit of G proteins?
GDP
In the basal state, are the a,b, and y subunits complexed together?
Yes
Which subunit has intrinsic GTPase activity?
a
Which subunit has lipid modification?
a and y
Is the y subunit hydrophobic or hydrophilic?
hydrophobic
What do lipid modifications do on G protein subunits?
tether them to the membrane (thus, only a and y are tethered to the membrane because b does not have lipid modification)
How does GCPR signal transduction begin?
An agonist comes in and binds to a receptor, promotes a conformational change in the receptor, and begins to interact with the G protein
What is the rate limiting step in GCPR signal transduction?
GDP release from the a subunit
When is GDP released from the a subunit?
When the GCPR binds to the G protein
What happens after GDP is released from the a subunit?
GTP (at high conc in the cell) and immediately binds to the empty GDP binding site on the a subunit- this process is unidirectional