turning signals on and off

Question 1

Which kinase is the exception when it comes to turning on mechanism?

Answer 1

RAF

Question 2

What is the standard method of turning on a kinase?

Answer 2

the kinase has 2 domains, one holds ATP and the other holds the substrate by positioning with the activation loop.
This activation loop is only in the correct orientation if phosphorylated

Question 3

How can a kinase be further inactivated beyond activation loop positioning?

Answer 3

Further inactivated by a pseudosubstrate loop which blocks the active site

Question 4

Which protein is important in the turning on of RAF?

Answer 4

14-3-3

Question 5

In the resting state, what conformation would you find RAF in?

Answer 5

In the resting state, RAF is phosphorylated at residues S259 and S621.
These 2 residues are clamped shut by 14-3-3

Question 6

What happens when activated RAS comes into contact with resting RAF?

Answer 6

activated RAS binds to RAF displacing one end of 14-3-3.

This allows phosphatase PP2 to dephosphorylates S259

Question 7

Which residue is phosphorylated to create fully active RAF protein?

Answer 7

Y341

Question 8

How is RAF deactivated?

Answer 8

residue S259 is rephosphorylated and 14-3-3 clamps the protein shut again.

Question 9

What are the three key ways in which a kinase is switched off?

Answer 9

1= internalisation of the ligand-bound receptor
2= phosphatases which are linked to scaffold proteins
3 = key parts of systems can be ubiquitinated and degraded

Question 10

How is SMAD signaling turned off?

Answer 10

SMURF ubiquitination complex transcribed by SMAD3/4 complex

Phosphatase dephosphorylates SMAD

Question 11

How is adrenaline signaling turned off in hepatic cells?

Answer 11

BARK phosphorylates ligand bound b-adrenergic receptor. Causes B-arrestins to bind and ligand/receptor complex to be endocytosed.
Protein kinase A also phosphorylates the receptor itseld = desensitises it. (this is feedback. PKA is main effector enzyme of the pathway)

Question 12

How is JAK STAT signaling turned off?

Answer 12

SOCS with SH2 domain bind the phosphorylated receptor - is a ubiquitin ligase.
Phosphatase with SH2 domain also binds

Question 13

How is rhodopsin signaling turned off?

Answer 13

Rhodopsin is phosphorylated by rhodopsin kinase to downregulate it

Question 14

How is nitric oxide signaling turned off?

Answer 14

Phosphodiesterase PDE5 converts cGMP back to GMP