Cyclic GMP Flashcards
What are the two types of guanylyl cyclase?
Soluble GC (cytosolic and NO sensitive) Particulate GC (membrane bound)
How many isoforms of pGC exist?
7 (A-G)
What domains does pGC have?
Extracellular Ligand binding domain Regulatory domain Catalytic domain Dimerisation domain (pGC exists as homodimers)
There are 3 groups of pGC what are they based on?
Their ligands
PGC A+B = bind to natriuretic peptides such as BNP which decrease TPR and increase diuresis
PGC C = binds to intestinal peptides
PGC D,E,F,G are orphan receptors
What is sGC formed from?
Hetrodimers of 1 alpha and 1 beta subunit
Multiple isoforms of the subunits exist
Catalytic activity of sGC is dependant on what?
The presence of both and alpha and beta subunit
SGC contains a heme group…why is this important?
NO (or CO) can bind here which increases endure activity by 100-200 fold
What are some functions of NO?
SM relaxation Neurotransmission Platelet aggregation Stimulates sGC Nitrosylation of proteins Neurotoxicity Induction of protein ADP ribosylation
How is NO formed?
Via Nitric oxidase synthase (nNOS, eNOS, iNOS)
This is a homodimeric protein
Why is calcium calmodulin important for NOS function?
Needed to aid/ complete the electron transport chain in the enzyme important for conversion of arginine + O2 -> citrulline +NO
What does PKG do?
Phosphorylates serine/threonine
Dependant on upstream amino acid sequence
Is PKG a monomeric protein?
No it is a homodimer
What are the types of PKG?
Type 1 (cytosolic) Type 2 (membrane bound)
What are the isoforms of type 1 PKG?
1alpha
1beta
Formed from alternative splicing
Structure of PKG monomer
N terminus
Regulatory domain - contains site of leucine zipper, cGMP binding and pseudosubstate
Hinge
Catalytic domain - contains ATP binding site and kinase area
C terminus
What does the pseudo-substrate of PKG do?
Autoinhibition via bind to kinase domain in catalytic domain area
What is the importance eof the leucine zipper?
Allows dimerisation for from PKG homodimer
What happens when cGMP binds to PKG?
4 cGMP bind to PKG dimer (2 for each regulatory domain)
Causes conformational change which releases pseudo-substrate from kinase area as monomers unfold.
Allows substrates to enter kinase domain and be phosphorylated
Name come PKG functions
Cardiac protection
Endothelial permeability
Smooth muscle relaxation
Neuronal plasticity
How does NO modulate vascular smooth muscle?
NO is made in endothelial cells in response to endogenous ligands such as bradykinin an d shear stress NO diffuses into VSMC Activates sGC Makes cGMP which activates PKG Relaxation
How does PKG mediate relaxation?
Phosphorylates myosin light kinase phosphatase which activates it and promotes dephosphorylation of myosin light chain (relaxation)
Inhibits RhoA. Since RhoA activates ROCK which intern inhibits MLCP PKG releases MLCP from inhibition
PKG activates RGS proteins which attenuate Gaq signalling via increasing their intrinsic GTPase activity thus decreasing calcium release
Phosphorylates IRAG which regulates the IP3 R on the SER = inhibits calcium release
Where is cGMP important for cycling nucleotide regulated ion channels?
Retinal rod cells
CGMP bound channels are open
Occurs during the dark state current
What isoforms of PDE degrade cGMP?
Specifically 5,6, and 9
Non specifically 1,2,3,10,11
How does cGMP regulate phosphodiesterase?
Alter rate of hydrolysis via competition for active site (PDE 1,2 and 3)
Allosteric modulation of activity (2,5, and 6)
