Lecture 12: Signal Transduction III Flashcards
GPCR molecular level
-difficult to work with bc integral membrane protein
-hard to isolate to study bc no like water
-difficult to crystallize
bovine rhodopsin
-1st GCPR structure determined in 2000
-binds retinol
-responds to light in eye
-one of easiest GPCR to work with
B2 adrenergic receptor structure
-took 7 years after bovine rhodopsin
GPCR timeline (GPCRdb)
-bovine first
-B2 7 years later
-now we have a lot more (1,102)
GPCR family
-largest class of btransmembrane proteins conserved thru evolution
Human GPCRs (not including olfactory)
~360
~120 orphans (ligand unknown)
~700 (~35%) drugs target > 135 GPCRs
*not targeting olfactory ones with drugs
Heterotimeric G-protein signaling
SLIDE SMTH
G-protein cycle
-association with agonist bound GPCR increases GDP release from Ga
-one agonist-bound GPCR can activate 10-100 G proteins
-intrinsic GTPase activity converts GTP to GDP
G-protein cycle Steps
- RESTING (GDP and Ga, GB, Gy)
- Ligand binding & nucleotide exchange
- Ga-dissociation (GB and Gy)
- ACTIVE (GTP on Ga on effector) = SIGNALING
- GTPase
- GTP hydrolysis
- Ligand-dissociation and trimer formation (Ga, GB, Gy)
Association with AGONIST bound GPCR INCREASES
DISSOCIATION OF GDP from Ga
Why does GTP bind
-lots of GTP inside the cell
-protein work is getting rid of GDP
guanine-nucleotide exchange (GEF) activity
-dissociation of GDP from Ga by agonist-bound GPCR
GTPase activity
converts GTP to GDP
one agonist-bound GPCR can activate
10-100 G proteins
GPCR is the GEF
true
monomeric vs trimeric?
-Ga, GB, Gy in trimeric?
Mechanism of GPCR activation of timeric G protien
- agonist binding
- G protein coupling and nucleotide exchange (GTP to GDP)
- activated G protein subunits regulate effector proteins (ATP to cAMP)
- GTP hydrolysis (lose phosphate) and inactivation of Ga protein
- Reassembly