Lecture 11: Signal Transduction II: Receptors Flashcards
signal receptors
-7TM
-GPCR
-LGIC
-kinases
Ligand-gated ion channels (LGIC)
-2 domains
-involved in neuronal signaling
LGIC mechanism
-first messenger (ligand) binds the channel receptor
-channel opens (gating) to allow ions to cross membrane
ions
Na+, K+ Ca2+
LGIC extracelllular domain
binds first messenger
LGIC transmembrane domain
pore through which ions flow
LGIC in neuronal signaling
-neurotransmitter ligands released from presynaptic neuron into synaptic cleft
-NT binds to channel, induces ion flow
-leads to quick post synaptic signal by changing the potential across the membrane
LGIC first messengers
-serotonin
-y-aminobutyric acid (GABA)
-nicotinic acetylcholine
-glutamate
-glycine
LGIC clinical relevance
-site at which anaesthetic agents act
-involved in BP regulation and cardiovascular disease
Nicotinic acetylcholine receptor
-Gating: binding to extracellular LBD triggers structural change to widen channel
-opening: sodium ions flow through open channel down gradient into cells
-depolarize post-synaptic membrane
Receptor tyrosine kinases
-ligands bind EC domains
-induce dimerization of receptor
-activates IC activity of receptor
-activated cytoplasmic domain phosphorylate on tyrosine to form specific binding sites
-leads to phosphorylation of other proteins
-termination by internalization with ligand dissociation and degradation
kinases examples
-insulin receptor
-growth factor receptors (epidermal, platelet-derived)
Kinase receptors
-many families
-various EC domains
-cell growth
-dysfunction=cancer
Besides receptor internalization, another way to terminate the signaling from receptor tyrosine kinases could be:
protein phosphatase as part of a protein phosphorylation cycle
Ras/MAP kinase signal cascade
-growth factor receptor binds growth factor ligand and initiates mitogen-activated protein kinase (MAP kinase) cascade
Ras/MAP kinase signal cascade mech
-activated Ras binds and activates MAP3K which triggers cascade
-SLIDE 9-10 pic
Activation of G-protein Ras
-molecular switch to activate cell proliferation, migration, transformation, survival
-signal activation involves: adaptor protein (Grb2) and GEF (Sos)
Ras mutations
-permanent activation of Ras enzyme
-big in pancreatic cancer
-HRas, KRas, NRas
-meds lacking
Activated Ras effectors
-PLCe
-RalGDS
-Raf
-PI3K
-so many and so many pathways = very problematic
KRAS structure
-hypervariable region (HVR)
-G domain
-active when GTP bound
-inactive when GDP bound
hypervariable region
-localization to membrane
G-domain
-switch I and II
-P-loop
-slide 12 pic
activation of KRAS
when GTP bound
inactivation of KRAS
when GDP bound
Ras
-membrane bound
-monomeric G protein
-activated by GF or by T cell receptors
P loop
changes here cause most cancer
Switch
-conformation of 2 loops based on GTP or GDP bound
Active Ras
-GTP bound
-binds specific effectors
-activates multiple pathways
Hydrolysis of GTP to GDP
-GTP to GDP
-rate increased by GTPase-activating proteins (GAP)
Guanine nucleotide exchange factors (GEF)
-increase GDP dissociation
-slow hydrolysis
-prolong activation of Ras
-promotes cancer
Slide 14
slide 14
Mutations KRAS
-single-base missense mutations in KRAS
-many in P-loop
-site varies based on cancer type
-decrease GTPase activity
-increase affinity for GTP
-KRAS always active = cancer
KRAS inhibition
-very difficult
-very high affinity for GTP and GDP
-mutant structure binds GTP with increased affinity
-constitutively active
Target G12C KRAS mutant
-irreversible inhibitor
-allosteric pocket in switch II
-lead compound that covalently links to C12
-covalently bound inhibitor prevents GTP binding
G-protein-coupled receptors (GPCRs)
-1000 different in human genome
-most common target of pharmaceuticals
-many hormone and NT receptors
-structural similarity
-signal via proteins
-no enzyme activity
-no scaffolding
GPCR structure
-7 a-helical transmembrane regions
-conformational change upon receiving signal
G-protein cycle (trimeric G protein)
-release of GDP is slow
-transient association w an agonist bound GCPR increases GDP release from Ga
=GEF activity
-one agonist bound GPCR can activate 10-100 G proteins
=BIG amplification
-intrinsic GTPase activity converts on to off form
-sometimes facilitated by regulators of G-protein signaling, RGS proteins
Desensitization
phosphorylation of GPCR residues in THIS region by kinase SLIDE 19
SLIDE 19
SLIDE 19
Heterotrimeric G-proteins that couple to GPCRs
-3 subunits Ga, GB, Gy
-association with agonist-bound GPCR induces dissociation of GDP and GTP binding
Ga
-GTPase activity
-20 subtypes
-dissociates from By complex and stimulates/represses effector protein when activated
