G Proteins Flashcards
Chapter 3
What are G proteins considered since they are controlled by two apposing enzymes?
conformational switches
Where do G proteins get their name?
G = guanine; named for their ability to bind to guanine nucleotides
In the conformational switch of G proteins, which “writer” switches GDP to GTP?
exchange
GEF
to ON state
In the conformational switch of G proteins, which “eraser” switches GTP to GDP?
hydrolysis
GAP
to OFF state
The binding of ____ to GTP triggers the GTP to form products.
effectors
Which phosphate on GTP plays a critical role in controlling G protein conformation?
gamma phosphate
it is typically the one that is hydrolyzed
On the molecular based of G protein conformation change, which two residues are held together by a third phosphate?
Gly (glycine) and Thr (threonine)
this forms GTP
How many G proteins does a typical eukaryotic cell contain?
~150
The G protein superfamilies consist of…
- small G-protein
- heterotrimeric G-proteins
What does GEF stand for?
Guanine-nucleotide exchange factor
What does GAP stand for?
GTPase-activating protein
The rate of the nucleotide exchange reaction and the nucleotide hydrolysis reaction are kinetically controlled by ____ and ____.
GEFs and GAPs
Study this figure
What factor controls the activity of GEFs and GAPs to control specific GTPase action?
upstream signaling inputs
What are the small G protein subfamilies and their respective function?
- Ras - cell proliferation/differentiation
- Rho - cell shape/movement
- Rab - vesicles
- Arf- vesicles
- Ran - nuclear import
Which small G protein is responsible for contraction in cell mobility?
Rho
RhoA - formation of actin-myosin contractile structure
Which small G protein is responsible for protrusion in cell motility?
Rac
Rac I - formation of actin-based protrusion
Which G protein is responsible for stress fibers?
Rho
Which G protein is responsible for lamellipodia?
Rac
Which G protein is responsible for filopodia?
Cdc42
What is this?
G-protein coupled receptor (GCPR)
What does this depict?
1) ligand binds to GCPR
2) Nucleotide exchange between alphaG by GCPR
3) Activated alphaG dissociates from betaG and gammaG
4) each binds to effectors to produce outputs
Activated GCPRs act as ____ to add phosphate to GDP.
GEF
Regulators of G protein Signaling (RGS) proteins serve as ____ to counteract the GCPR.
GAPs
Rho GEFs and GAPs serve as an ____ ____ that allows upstream inputs to plug into common G-protein mediated output responses.
adaptor layer
Many GEFs and GAPs are ____ and can dictate specific protein and lipid interactions.
modular
What does this depict?
GEF and GAP catalytic domain recruitment to the sites of G protein action
What does this depict?
Activiation by relief of auto inhibition via ligand binding or phosphorylation
What does this depict?
Activation of RhoGEF by ligand binding
Most G proteins bind both GTP and GDP with high affinity and have half-times for dissociation in ____ to ____.
minutes to hours
How do GEFs generally act in a mechanism?
They modify the structure of the nucleotide binding pocket, resulting in reduced affinity for the nucleotide binding.
How does GTP bind to the G protein after interacting with GEF?
It is driven by the much higher intracellular concentration of GTP
What is the mechanism of GAP?
GAP binds to active GTP and with the hydrolysis from a water molecule, causes the removal of a phosphate, creating GDP.
When GAP interacts with the G protein binding pocket, what is the the known structure that associates with GAP?
arginine finger
stabilizes the phosphate in the G protein pocket
Many G protein have ____ ____ attached at the C-termini for membrane localization and function.
lipid groups
Binds to specific G protein and shields the lipid group to maintain the G protein in the cytoplasm; locks in its GDP bound form and prevents their localization to the membrane.
guanine nucleotide dissociation inhibitors (GDIs)
Promotes the release of GDI from G protein, allowing G protein localization to membrane.
GDI displacement factors (GDFs)
permanent lipid attachment
integral protein
What does the MAP kinase cascade do?
After an input, the MAPKKK becomes phosphorylated, after entering a new cycle, it loses a K, MAPKK becomes phosphoylated, enters a cycle and loses a K, then finally MAPK is phosphorylated and produces an output.
How do scaffolds work with MAPK cascades?
They help to physically organize the MAPK components
What mechanism of scaffold proteins controlling information flow is being depicted below?
increasing the effective concentration of two interactive proteins through tethering and enhanced proximity
What mechanism of scaffold proteins controlling information flow is being depicted below?
preventing the protein from interacting with alternative partners and substrates
What mechanism of scaffold proteins controlling information flow is being depicted below?
the scaffold itself may serve as an allosteric regulator to make a pathway protein active upon binding to scaffold (inactive without scaffold interaction)
