Phosphorylation – kinases and phosphatases Flashcards
(59 cards)
What does phosphorylation central to and what does it mean
Phosphorylation is central to cell signal transduction
This is the transfer of a phosphate group (PO4) to another biological molecule
What does the phosphorylation of enzymes do
Phosphorylation of enzymes could enhance or decrease its ability to catalyse reactions
The 3D shape changes due to different charges present on different amino acids – opposite charges attract which could cause the shape of the protein to change
This can activate or inactivate enzymes
These reactions are reversible – a key part of any signalling pathway
What type of modifications are phosphate groups
Covalent
Where to the phosphate group come from
The phosphate comes from ATP – Gibbs free energy makes ATP losing its outer most phosphate group favourable
What can change during signal transduction
Protein conformation
Ionic concentration
Phosphorylation
The level of cAMP – and other endogenous chemical signals
Redox potentials
A change in protein conformation can be accomplished in various ways with phosphorylation being a key example
What are the 3 targets of phosphorylation
Serine
Threonine
Both of these have a terminal hydroxyl group which is the target
Tyrosine
Also has a terminal hydroxyl group on the end of its aromatic ring
What phospharylates serine and threonine
Serine and threonine share a similar Ser/Thr kinase
What phosphorylates tyrosine
Tyrosine is aromatic so has a different shape – Tyr kinase
What is the target in protein prokaryotes
In prokaryotes, histidine is the target
The nitrogen of the imidazole ring is the target of phosphorylation
This is catalysed by the His kinase
Why is conformation changes important in cell signalling
Change can open membrane channel proteins
Change can expose interaction sites – like SH2 or SH3
Motifs/ domains exposed
Change may alter enzyme activity negatively or positively
What are the features of a good signal
Specific
Small
Can be mobilised or altered quickly
Is reversible (can be switched off)
What are phosphorylation motifs
Reversible phosphorylation is ubiquitous in signal transduction cascades
Consensus sequence (motifs) direct the target of phosphorylation
What are the different types of kinases
AGC = PKA, PKG and PKC
CMGC = MAP kinases & CDK’s
PTK = Tyrosine Kinases
CaMK = Ca2+/calmodulin dependent kinase
Others = Phosphorylase kinase, hexokinase…..
What are important types of Ser/Thr kinases
PKA = cyclic-AMP dependent protein kinase
PKG = cGMP dependent protein kinase
PKC – controlled by cleavage and multiple second messengers (IP3, DAG, Ca2+ etc)
CaM kinase – caslcium / calmodulin dependent protein kinase
All the above are Ser/Thr kinases, however they are activated by different second messengers
What are the features of PKA (or cAPK)
is widespread in eukaryotes
Is controlled by intracellular cAMP levels
PKA is found as a tetramer when inactive which contains 2 catalytic subunits and 2 regulatory units
Once activated PKA can phosphorylate the next component in the signal transduction cascade
What are the features of PKG
Is activated by cGMP
PKG is therefore activated under different circumstances and its downstream effects are different to PKA
The activation of PKG is central to vasculature tone
Is abundant in the heart, lung and smooth muscle
What are the features of PKC
one of the most important
Is a family of kinases which contains many different isotypes
Deferent versions arise from different genes but also mRNA alternative splicing
PKC activity is regulated in numerous ways
What important domain does PKC have
a regulatory domain – this is a target for a number of different second messengers which include IP3 and DAG
What are the features of CaM kinase
calcium ions are central to cell signalling processes due to it altering the function of numerous proteins through ionic interactions
One target for intracellular Ca2+ is a class of proteins known as Ca2+ / calmodulin dependent kinases - CaM kinase
What happens once CaM kinase is activated
Once activated through calcium ion binding, calmodulin can interact with a number of different proteins
What CaM kinase is ubiquitous and what’s its shape
Many classes of CaM kinase – the best characterised is CaMK-II or just kinase-II
This is ubiquitous but is most abundant in the brain
It is a dumbbell shape which contains four EF hand motifs
What does the consensus sequence for tyrosine kinase contain
The target phosphorylation consensus sequence for Tyr kinase contains an N-terminal “acidic” amino acid (Asp or Glu) 3-4 residues from the Tyr-PO4- target
What groups are RTKs in
RTKs are split into 14 groups which all carry the same topology/structural patterns
What does phosphorylation of RTKs do
Phosphorylation of this kinase leads to intracellular signal transduction
