L10 Intracellular Signalling Flashcards
What cannot cross the lipid bilayer?
Proteins, peptides and charged molecules
What are integral membrane proteins?
Transmit signal into the cell and span the membrane
Ligand may interact directly or indirectly
How are signalling molecules controlled?
Post Translational Modification - phosphorylation
Regulating G protein’s GDP or GTP
Provision of activators - calcium ions
What is kinase?
An enzyme that phosphorylates proteins
What is phosphatase?
An enzyme that dephosphorylates proteins
What do protein kinases and phosphates act on?
OH group of serine, threonine and tyrosine (free hydroxyl groups)
Serine/Threonine kinases examples
Ca2+/calmodulin-dependent protein kinases or CaM kinases Protein Kinase A (PKA) Protein Kinase B (PKB) Protein Kinase C (PKC) Mitogen-activated protein kinases (MAPK)
Tyrosine kinases examples
Non receptor tyrosine kinases e.g. Src family kinases -
Receptor tyrosine kinases (RTKs) –
e.g. Insulin receptor
Epidermal growth factor receptor (EGFR
What are GTP binding proteins?
Many GTP binding proteins are individual proteins (small GTPases)
Used by heterotrimeric G proteins
Hydrolyse GTP-GDP by intrinsic GTPase activity (act as molecular switch)
What do ion channels do? [4]
Transport Na+, K+, Ca2+, Cl- Ions along an electrochemical gradient
Specificity of the channel is defined by the amino acids lining the channel
Fast regulated opening/closing mechanism (mSec)
Channels are formed of protein subunits
What are voltage gated ion channels?
Voltage gated ion channels open in response to a change in voltage
The alpha-subunit of the Na+ channel contains the pore and has 4 homologous domains, each with 6 TM regions
Region 4 of the alpha-subunit contains amino acids with positive R-groups which sense the voltage across the membrane causing movement of region 4 which opens the channel
What are ligand gated ion channels?
Transmembrane proteins consisting of a receptor part and a channel which traverses the membrane
Open in response to binding of a ligand
Receptors are often classified based on which agonists they bind
What events are regulated by calcium ions? [4]
Secretion of enzymes, hormones and neurotransmitters
Changes in some transcription factor activities
Skeletal muscle contraction
Development of an egg upon fertilisation with sperm
What mediates calcium ion effects?
Calmodulin which binds Ca2+ and activates other proteins
CAM kinases calmodulin-dependent protein kinases
Calcineurin Ca2+-dependent protein phosphatase
How many transmembrane domains do GPCRs usually have?
7
GPCR initiation of signalling
Action of the receptor causes GDP attached to alpha subunit to be replaced by GTP
G-protein splits up in beta-gamma complex an α-subunit
Both complexes then initiate further cell signalling
GTP is then hydrolyzed to GDP and beta-gamma recombines with alpha ready to associate with another GPCR
Adenylate cyclase and cAMP
Adrenaline + GPCR
Activated adenylyl cyclase
cAMP activates PKA
Gs
Phospholipase C Activation
Phosphorykates inositol phospholipid tp form inosition 1,4,5-triphosphate and diacylglycerol -> PKC
Gq
GPCRs and K+
Muscarinic ACh receptor in heart
ACh bind GPCR and activate beta-gamma unit, which binds potassium channel = open
Hyperpolerisation
Cholera
Cholera toxin
Inhibits the GTPase activity of the
subunit Gαs (stimulates adenylyl cyclase)
Prolonged signal causes water and Cl- to
move out of the cells lining the intestine
Results in diarrhoea, dehydration and death
Whooping Cough
Pertussis toxin
Renders Gαi inactive (inhibits adenylyl cyclase)
Prevents Gαi from associating with GPCRs
Prolonged signal that stimulates coughing
Enzyme receptors
The cytoplasmic enzymes that induce signalling are normally protein tyrosine kinases
These receptors usually have a single membrane spanning domain
Receptor tyrosine kinases
Ligand binding activates an enzyme activity associated with the cytoplasmic domain
The response usually requires receptor dimerisation
Pairs of tyrosine residues in the intracellular domains are
auto-phosphorylated in response to the signal
JAK-STAT
In the JAK-STAT pathways a ligand binding to its receptor activates an associated protein tyrosine kinase, which directly phosphorylates and thus activates a STAT transcription factor
