lecture 22- other protein kinases and protein phosphatases

Question 1

protein kinases activated by cyclic GMP

Answer 1

protein kinase G

Question 2

other protein kinases activated by increase in calcium

Answer 2

protein kinase C
calcium/calmodulin dependent protein kinase
protein kinase B and protein tyrosine kinases (phosphorylate tyrosine)

Question 3

cGMP signalling pathway

Answer 3

GPCRs are not involved
cGMP is generated by guanylyl cyclase (GC)
there are to types of GC
1. soluble form activated by NO
2. plasma membrane bound form activated by small number of peptide agonists (unlike AC which has longs of agonists)
cGMP binds to protein kinase G to activate it
cGMP is broken down by cGMP dependent PDEs

Question 4

cGMP in smooth muscle causes

Answer 4

relaxation

Question 5

NO (which stimulates soluble guanylyl cyclase to make cGMP and activate PKG and cause a response) to is made by

Answer 5

NOS (type e,n or i)
calcium can stimulate NOS

Question 6

cGMP in health and disease

Answer 6

NO is release from endothelial cells and activates sGC in smooth muscle cells, leading to vasodilation and decrease in BP

Question 7

NO generating drugs often used to treat

Answer 7

treat angina

Question 8

LPS (toxin from gram negative bacteria)

Answer 8

stimulates expression of the iNOS causing excessive NO production which can lead to clinical shock and severe drop in BP

Question 9

viagra

Answer 9

cGMP phosphodiesterase inhibitor
produces smooth muscle relaxation in certain tissues

Question 10

protein kinase c - 3 groups

Answer 10

cPKC, nPKC, aPKC
single polypeptide, has regulatory domain and catalytic domain
all require phospholipid binding to be active
pseudosubstrate (PS) motif on the R domain keeps the kinase inactive by binding to the substrate binding site on the catalytic domain until there until there is a rise in calcium

Question 11

PKC

Answer 11

agonist activates phospholipase c
then you get IP3 and DAG
IP3 causes calcium increase
calcium binds to domain on C2 on the R domain
this changes C1 domain which now adheres with DAG (translocate to plasma membrane)
PKC then can phosphorylate substrates as the PS motif has disengaged from catalytic (C4 domain)

Question 12

calcium/calmodulin dependent protein kinases

Answer 12

2 main types
- those that show narrow substrate specificities E.g phosphorylase kinase, only phosphorylates phosphorylase
- those with broad substrate specificities
e.g. multifunctional CaM kinase II

Question 13

when calcium levels go back down you still have CaMKII

Answer 13

inactive kinase cant bind to anything as the catalytic domain is bound to the autoinhibitory domain
rise in calcium, it can bind to calmodulin, calmodulin changes shape and it can interact with the CaMKII
conformation change and the catalytic domain can interact with substrate and can phosphorylate it
autophosphorylation - catalytic subunit can phosphorylate one next to it, it then traps calcium calmodulin meaning its not released so the CaMKII can continue to phosphorylate after calcium goes down

Question 14

protein phosphatases (PPs)

Answer 14

remove the phosphate groups from phosphorylated proteins
4 major classes - 1,2A-C
2B requires Ca/CaM for activity
PPs are themselves regulated by inhibitory proteins

Question 15

chemical inhibitors of protein phosphatases

Answer 15

okadaic acid - blocks PP1 and PP2A
cyclosporin A

Question 16

inhibitory proteins

Answer 16

PKA phosphorylates phosphorylase kinase which phosphorylates phosphorylase which begins the process of glycogen breakdown
as this happens PKA also switches on phosphatase inhibitory proteins by phosphorylating it causing it to bind to phosphatases and block their activity

Question 17

cAMP and calcium in skeletal muscle synergy

Answer 17

glycogen breakdown from cAMP pathway provides ATP for muscle contraction from calcium release

Question 18

phosphorylase kinase

Answer 18

PKA phosphorylation of alpha and beta subunits on the phosphorylase kinase increases the calcium sensitivity
need more energy for muscles to contract so systems are integrated