Mechanisms of Cell Signalling Flashcards
Response types and examples
Reversble-become motile/change shape
Irreversible-divide, differentiate/remain undifferentiated, die
Cells sense environment bye
Specialized receptor proteins
Ligands+specificity
Molecule that triggers signal by binding to receptor
-specificity governed by tertiary structure and non-covalent bonds between AA groups
Agonists vs antagonists
agaonists-induce receptor activation
-occupies ligand binding site and stimulates receptor activity
antagonists-block receptor activation
-occpies ligand binding sites and exclusde agonists /change conformation of receptor
where do drugs act
either receptors or enzymes
Ion channels
Pore forming protein that allow flow of ions across membranes down electrochemical gradient
Ligand gated channel
Bind ligand to open channel to allow flow of ion across membrane-or close to slop flow
Basis for nerve transmission and muscle contraction
Channels are oligomeric (can form groups that do not let anything through)
CFTR
Cystic fibrosis transmembrane conductance regulator
- recessive disease-loss of function mutation
- abnormal salt transport-mucous buildup
- ligand=ATP
GOF mutations to ion channels
Domnant inheritance-create defects in other ion channels b/c oligomeric bonding
-only 1 bad receptor fucks up others
Mutations in voltage=dependnent Na” channels
GOF
Results in defective inactivation and late Na+ currents
Tetrodotoxin
Pufferfish toxin
-Na+ channel blocker-blocks action potentials in nerves
Nucelar Steroid hormone receptors
Derived from cholestorl-control gene expression
Hydrophobic hormones-cross cell membrane
Bind to receptors in cyto or nuc
Chaperone may help prior to ligand binding
Estrogen
Enter cell, binds to chaperone, binds to receptor, receptor causes estrogen dissociation from chaperone and exposes nuclear import signal=homodimerizaiotn and nuclear entry occur
Bind to ERE (dna promoter) to activate gene trx
Estrogen receptors are overexposed in breast cancer cells
Endocrine therapy for breast cancer
Use selective estrogen receptor antagonists-tamoxifen
Protein Kinase receptors Pathway
Ligand binds to extra cellular domain
Subunits dimerize-cytosolic protein kinase domains are now in proximity
Kinases phosphorylate each other (usually multible P’s)
Additional cytosolic proteins recruited to receptors (bind to phosphorylated tails)
Phosphorylation
Reversible
On/Off switch
Can turn hydrophobic portion of a protein into hydrophilic
Conformational change-facilaitate interaction
Grb
G-protein receptor binding
Binds to phosphylated g receptors
Constains SH2-doman that recognizes phosphorylated kinase (tyr-P)
Tyr-P
AA that gets phosphorylated in protein receptor kinase cascade
SoS
GEF=son of sevens
-bnds to grb and activates small G-prtoeins such as Ras
Ras
Monomeric small g=protein, activated by SoS
GEFs
Guanine nucleotdie exchange factors
Activate G proteins (like RAS) by catalyzing exchange of GDP for GTP
GAPs
GTPase activating proteins
Promote inactivation o G prpteins by cleaving phosphate group from GTP to make GDP
G-proteins
Bind guanine nucleotides and act as molecular switch during signalling
DRAW-NUCLEOTIDE EXCHANGE REACTION AND G PROTEIN=SLIDE 30
SoS recruited to actiate protein kinase receptor-induce exchange of GDP for GTP on Ras
- Ras is inactive with GDP bound
- SoS is ras GEF
- Ras is now activated-weak gap function, hydrolyzes GTP to GDP slowly (weak gap function) there is also gap proteins that push process along wit proper timing to allow inactivation of as from GTP to GDP
- intrinisic and other proteins push along GTP to GDP
Ras-MAPK pathway
DRAW
ras stimulates phosphrylation cascade
- MAPK, KK, KKK etc.
- target is TF in nucellus-activate it and allow regulation of gene expression
- result=cell division
Ras functions
Cell growth/dividion, cytoskeleton, membrane traffic-many more
Depends on what is downstream
Oncogenic mutations in Ras
Turn all downtstream pathways on
- two position-gl-12/13 or gln-61
- abolish weak intrinsic function of as to dephosphorylate self
- cant hydrolyze GTP to GDP
Neurofibromatosis Type 1
Mutation in NF1 gene
- Encodes a Ras GAP
- catalyizes converson of GTP to GDP
- overactive Ras if can’t
Noonan Syndrome
Mutation in PTPN11 gene which encodes SHP2
-GOF which leads to hyperactive ras
7 alpha helix receptors
Must abundant -7 transmembrane alpha helixes with large extra cellular domains (also have intracellular part) -Most drugs target at these -Coupled to large G-proteins
Roles of 7 a helix receptors
vision, smell, mood, autonomic nerve system
7 alpha helix receptor pathway
Ligand binding causes exhchange of GDP by GTP and activates G-protein
-alpha domain has GTP whhile beta and gamma spread away
Functions of gsalpha, go-alpha, and gpalpha
Stem from G-alpha
Gs-stimulating pathway downstream
Gi-inhibiting pahtway
Gs/Gi-function through adenylate cyclase-target PKA
Gq-alpha-actviates and targets PKC
B andrenergic receptor (DRAW)-42/43
7-alpha helix receptor
-binds to epinephrine and norepinephrne
-ligand bound receptor is substrate of BARK
- Phosphorylated receptor is bound by beta arresting
- terminates signal even in presence of ligand
- BETA ARRESTIN BINDS ONTO THE B ANDREGENIC RECEPTOR-no alpha, beta, gamma subunits recombine to resend signal
Blocks interaction with Gs
DESENSITIZATION PATHWAY
Gs alpha/Gi-alpha DRAW-44
Target is protein kinase a (PKA)
- blocks reaction of inactive adenylate cyclase to active adenylate cyclase
- cuclic amp then goes on to activate protein kinase a
- regulates untra cellular calium
- gsalpha and gi alpha antagonistically work to regulate PKA activity
AC/PKA induced Ca 2+ signalling
Cyto Ca 2+ is maintained at very low concentration by calium pumps in PM and SER
- receptor mediated calium influx triggers many events in cell
- ligand/recepptor doesn’t really matter-depends on what g protein is linked
Gq proteins acticate PKA via Ca2+ and PLC
Regulate PKC
- PLC on cell membrane
- hydrolyze Pip2-make DAG and IP3
- DAG goes to activate PKC directly-allows Ca 2+ to go in
- IP3 in presence of Ca goes into cell, allows more calum from lumen of SER to go to sit
- DAG plus calcium from IP3 regulate protein kinase C
Why need calcium and ligand for protein kinase c (DRAW 48)
PKC is inactive b/c active site is filled with N=terminal psuedosubstrate peptide held in place by C1 and C2 domains
- C1 domain binds DAG in membranes
- Presence of Ca2+ in C2 domain binds phosphatidyl serine-found in inner leaflet of PM
- This removes psuedosubstrate from active site and PKC becomes active
- Can then be cleaved and kinase now is permanently active
Calmodulin
Binds to Ca2+ (4 at once) and regulates activity of many proteins
-activates calmodulin-activated protein kinase (CAMK)
CAMK
Calmodulin with 4 Ca2+ bind to it, active site is not accessible
-linked to learning, memory, cancer, and musculoskeletal diseases
