BLOCK 5 Lecture 1

during exercise - overview

AMPK overall

So then when you stop using ATP the leves will go back up and this will switch off AMPK

ATP inhibits AMPK because AMP gone down enough

activation of AMPK

So other than ATP kinases can also act on AMPK to maintain balance in cell

There are 4 of these:

LKB is constitutively active and can P AMPK

At the same time there is a dephosphorylase PP2Ca which de phosphorylates at the same site

AMP is a negative regulator of phosphorylase (PP2Ca) activity so get more P of AMPLN than dephosphorylation

In some cells also have different activators - specific to the cell type

AMPK has 3 subunits

AMPK structure

 

P happens at the alpha subunit at a specific tyrosine residue

This is within the kinase domain - the domain which phosphorylates other proteins

Also has an AID and beta binding domain - needed for binding to beta subunit

Bta subunit has glycogen binding - important in liver and alpha binding domain - mostly is just there to hold the alpha and beta together

Gamma senses the amount of AMP vs ATP in the cell

Has 4 CBS domains which can each bind AMP or ATP

All bound to AMP leads to activation of AMPK as long as upstream kinases have also P the alpha domain

Depending on what combo of alpha beta and gamma you have a in specific cell, that can change the activation state and whether stuff upstream can activate

Can have 12 different potential combos which will all suubtely change the activity

Because it changes the conformation when bound at all of these sites

AID is the inhibitory domain - change in conformation makes it move away so that kinase domain can be activated

AMPK in contracting muscle

When AMP is high we want catabolidm - want to use more glucose and more ATP - want glycolysis

Hexokinase and phosphofructokinase in the glycolysis pathway are activated by P by AMPK

So pushes more glucose down this pathway

 

Also first to get the glucose need to activate the glycolysis pathway

getting fatty acid into the mitochondria

once fatty acids are in the muscle need to get to mitochondria for fatty acid oxidation

Fatty acids need to be moved into the matrix of the mitochondria in order to be made into ATP

But cant get through the inner membrane without a transporter - need a carnitine shuttle

AMPK can block ACC2 which activastes malonyl-CoA which usually inhibts this pathway - so overall ends up activating CPT1 - allows more fatty acids to be transported into the matrix of the mitochondria so more beta oxidation can occur

switching off anabolic pathways

AMPK overall diagrams

First need to get fatty acids out of the bloodstream and into the muscle cells - 2 different transporters

GLUT4 for glucose

CD36/FAT receptor for fatty acids

GLUT4 can be stimulated at the expression level by AMPK signalling so get more made in muscle cells

Also stimulates the transloaction of GLUT4 into the membrane to transport glucose into the cell

FAT receptors also sit in intracellular vesicles and when they are required AMPK stimulates translocation into membrane through P

Both allows icnreased transport into the cell

Then fatty acids have to get into the mitochondria - metnioned above how it is also regulated by AMPK

Can also limit protein synthesis by blocking TOR

AMPK exam pathways

Shows how complex these pathways are

Somewhat simplified but still complex

E.g. insulin

Insulin ligand binds to the receptor and activates PI3K

Then have a couple steps which leads to activation of Akt then mTOR

mTOR can activate or inhibit various components

Inhibits protein synthesis

Akt can also inhibit AMPK by blocking PI3K which would usually promote protein synthesis

Basically saying you can use this diagram to go thrrough the various pathways

So don’t need to menorise just interpret