protein pathways

RAS/MAPK pathway

1. RAS binds to GTP and gets activated

2. RAS interacts with RAF (S/T kinase)

3. RAF phosphorylates MEK (S/T kinase)

4. MEK phosphorylates ERK/MAPK (S/T kinase)

5. MAPK activates transcription factors

RAS/MAPK pathway is the what pathway

cell growth/proliferation pathway

RAS/MAPK pathway mutations are bad because…

• cell growth/proliferation is out of control

• causes tumors/cancer

MAPK

mitogen-activated protein kinase

second messengers

• small so they move/diffuse fast

• amplify original signal

• created/destroyed quickly

• noncatalytic-activation is through physical interactions

hydrophobic second messengers

• diacyglycerol (DAG)

  • created through catalytic process

• phosphatidylinositols

• diffuse from plasma membrane

• regulate membrane-associated effector proteins in the intermembrane space

hydrophilic second messengers

• located in cytosol

• cAMP

  • created through catalytic process

• Ca 2+

• IP₃

  • created through catalytic process

gases (second messengers)

• NO

• CO

• H2S

• diffuse through cytosol and plasma membrane

G_s protein pathway

1. GPCR and ligand bind together

2. GPCR gets activated

3. GPCR stimulates exchange of GDP for GTP in the alpha subunit of the protein and the rest of the G-protein activates

4. alpha subunit of G_s protein and adenylyl cyclase interact w eo

5. adenylyl cyclase gets activated and interacts with ATP to create cAMP

6. cAMP binds with protein kinase A (PKA) inhibitory subunits and it causes 2 active kinase catalytic subunits to get activated and break away

7. activated PKA subunits go into the nucleus to make changes in gene expression

• overall goal is increased protein phosphorylation

what is adenylyl cyclase

membrane bound enzyme

what is cAMP

a second messenger

what is protein kinase A

• has 2 inhibitory subunits and 2 active subunits

• requires 4 cAMP molecules to active

• 2 active subunits break away once active (conformational change)

• adenaline ad epinephrine stimulates PKA activation

• mediates fight/flight response

G_i protein pathway

1. GPCR and ligand bind together

2. GPCR gets activated

3. GPCR stimulates exchange of GDP for GTP in the alpha subunit of the G-protein and the rest of the G-protein gets activated

4. G_i protein and adenylyl cyclase react with eo

5. G_i protein inhibits adenylyl cyclase from working

• no cAMP is made

• protein phosphorylation decreases

G_q protein pathway

1. GPCR and ligand bind

2. GPCR gets activated

3. GPCR stimulates exchange of GDP for GTP in the alpha subunit and the rest of the G-protein activates

4. activated G_q protein activates phospholipase-C

5. phospholipase-C breaks down a phosphoinostiside into DAG and IP₃

6. IP₃ binds to an IP₃ ligand gated channel in the ER

7. channel opens and Ca²⁺ floods the cytosol

8. protein kinase C gets activated by…

• Ca²⁺ binding

• diacylglycerol (DAG) binding

• phosphotidylserine binding (phospholipids in the membrane)

9. active PKC stimulates secretory vesicle fusion to the plasma membrane

• protein phosphorylation increases and so does the activation of Ca²⁺ binding proteins (like calmodulin)

phospholipase-C

phospholipid enzyme

calmodulin

• small protein

• turned on by Ca²⁺ binding (4)

• binds and activates additional proteins like CaM kinase

• important effector to Ca²⁺ signaling

G-protein inactivation and negative feedback loop

• G-proteins quickly inactivated following interactions with other proteins —- happens naturally

• negative feedback loop

  • activated GPCR stimulates GRK (GPCR kinase) to phosphorylate it

  • phosphorylated GPCR attracts arrestin (inhibitory protein) and arrestin binds to it

    • GPCR is inactivated/inhibited