lecture 23 Flashcards
what are the ways protein kinases are activated by?
-cyclic GMP (activation of protein kinase G)
-increase in Ca2+ (PKC and Ca2+/calmodulin dependent PK)
what are the features of the cyclic GMP signalling pathway?
-GPCRs NOT involved
-cGMP generated by guanylyl cyclase (GC)
what are the two types of guanylyl cyclase?
- soluble form (sGC) - activated by nitric oxide
- plasma membrane bound form (pGC) -activated by small number of peptide agonists
what does cGMP do?
-binds to protein kinase G to activate it
what does PKG phosphorylate?
serine and threonine residues
what is cGMP broken down by?
cGMP dependent phosphodiesterases
how is NO produced?
made by enzyme nitric oxide synthase (NOS)
made by epithelial cells
what is the summary of NO pathway?
-NO gets into cell and activates the soluble GC to make cGMP
-goes on to activate PKG and phosphorylate target proteins to get a response
how is pGC used to produce cGMP?
-able to bind to a variety of peptides (ANP)
-activates GC to make cGMP pathway
-built in activation as no G proteins
how is nitric oxide used in health and disease?
-released from endothelial cells
-activates soluble GC
-vasodilatation and increases blood flow
-used to treat angina (chest pain caused by too little blood flow to heart)
-helps with blood pressure control
how is LPS (endotoxin) used in health and disease?
-gram negative bacteria gotten from systemic infection
-stimulates expression of iNOS (inducible NOS)
-causes excessive NO production
-can lead to clinical shock as severe drop in BP- gets so low the body shuts down resulting in death
how is viagra (sildenafil) used in health and disease?
-type 5 cGMP PDE inhibitor
-produces smooth muscle relaxation in certain tissues
-treats erectile problems and pulmonary hypertension
how is CFTR used in health and disease?
-in intestine
-heat stable enterotoxin from E.coli
-switches on pGC
-cGMP activates PKG which phosphorylates CFTR
-overstimulation of cells
-cholera toxin - irreversible changes
-leads to secretory diarrhoea
what are the 3 groups of protein kinase C?
-conventional (need increase in calcium and bind to lipids to be activated)
-novel
-atypical
what is the structure of protein kinase C?
single polypeptide
regulatory and catalytic domains
11 different isoforms
require phospholipid binding to be active
what is a pseudo substrate motif (PS)?
-in R domain
-keeps kinase inactive by occupying the substrate binding site on the C4 domain
-keeps in OFF position until needed to be activated
what is the process of the activation cycle for cPKC?
- Ca2+ binds to C2 domain, PKC translocates to plasma membrane - binds to DAG via C1 domain
- causes PS motif to disengage from catalytic (C4) domain, so substrates can bind and get phosphorylated
what chemicals can artificially activate?
phorbol esters -plant alkaloids that are tumorigenic
bind directly to PKC
what are the two broad types of Ca2+/calmodulin dependent protein kinases?
- have narrow substrate specificities eg. phosphorylase kinase only phosphorylates phosphorylase
- with broad substrate specificities eg. multifunctional CaM kinase ll (CaMKll)-phosphorylates many
what are the functions of CaMKll?
- associates with NMDA receptors
- enhances InsP3 formation
- plays role in frequency decoding of calcium signals
- phosphorylates phospholamban to control pumping of SERCA2 pump
what do protein phosphatases do (PP)?
-remove phosphate groups from phosphorylated proteins (serine/threonine/tyrosine)
what are the 4 major classes of Set/Thr protein phosphatases?
1, 2A, 2C = broad and overlapping substrate specificity
2B (CaN) = restricted specificity - requires Ca2+/CaM for activity
what are PPs regulated by?
inhibitory proteins
what are the chemical inhibitors of protein phosphatases?
-okadaic acid = blocks PP1 and PP2A
-cyclosporin A = specific for calcineurin (2B) - used for immunosuppression via effects on T cells
