COVALENT: cAMP, PKA, and glycogen metabolism

Question 1

covalent mod is related to

Answer 1

2ndary messengers/hormones

Question 2

PKA

Answer 2

protein kinase A, PKA gets activated by cAMP in response to glucagon, which is the lower BS hormone.

Also known as cAPK cAMP dep. protein K)

Question 3

concentration of cAMp intracellularly,

Answer 3

will determine fraction of active PKA… (refer to cycles diagram at the top)
Will control +Pi of serine and threonine in PKA’s substrates: PhK, GS, PPi1

Question 4

How does cAMp affect both +Pi and -Pi

Answer 4

affecting phosphorylation of phK and GS, and affecting phos of PPi1 which will affect dephospho system (If inhibitor is not phosphorylated, not inhibiting the dephospho process… if +Pi, then is inhibiting)

Question 5

no cAMP present

Answer 5

PKA is inactive tetramer with four subunits… R and C subunits… (R2C2)
R = b and a domains, on reg subunit, which affect the ability of reg subunit to keep catalytic sub inhibited or not inhibited. …. has autoinhibitory segment.
These are known as AI
This AI of R (segment) will bind to C SU active site, which will be a CI.

Question 6

When cAMP bind to PKA

Answer 6

4 cAMPS will bind, cause two C SU’s to become independent and exist on their own which is why it is 2C…. and a regulatory SU is staying stuck together with cAMP sticking out, which means reg SU cannot inhibit anymore due to presence of cAMP.

Question 7

Domain B and domain A with helix

Answer 7

like earmuffs when opening and closing.
2 cAMP will bind cooperativly to two domains (A and B) in each R SU, each ear muff pop off, helix bend and will close. (when cAMP bound)

WHY? so cAMP can bind (also to release C)

Question 8

cAMP binding cooperativity

Answer 8

binds to the R subunit’s B domain first, causing a change in conf which opens up R subunits A domain (cooperativity) so cAMP can bind easier now .
C subunits now released and can operate independently. For this to occur, the helix between B and A domains bend into 2 helical segments.
This will unwrap the “open ear muffs” (R subunit from large lobe of C) and breaks all interactionswith C SU, removing AI segment.

Open ear muffs: A nd B domains must lose cAMP binding sites, so cAMP

Question 9

Open ear muffs losing cAMP binding site

Answer 9

Open ear muffs: A nd B domains must lose cAMP binding sites, so:

cAMP will have phosphate and adenine binding pockets, which should be close together, so have to separate these. Want to get rid of these pockets through conf selection.
conf: will remove or align the AI from the AS or into the AS cleft. For AI to remove, bilobal (catalytic) SU is active. Deep cleft between the subunits, Mg and target sequence both bind here.

Target seq:
has serine or threonine that can phosphorylated.

Question 10

C subunits threonine

Answer 10

permanently phosphorylated as threonine 197 phosphate, (post trans mod) at the mouth of the cleft, and will orient the AS AA’s via ion pairng with Arg (known as a lock up)
This ensures orientation of Asp 166, which will locate target seq and get rid of a H on serine in PhK, or PPi-1 so O- can do a nuc attack on phosphate.