Lecture 11: Signal Transduction II: Receptors

Question 2

signal receptors

Answer 2

-7TM
-GPCR
-LGIC
-kinases

Question 3

Ligand-gated ion channels (LGIC)

Answer 3

-2 domains
-involved in neuronal signaling

Question 4

LGIC mechanism

Answer 4

-first messenger (ligand) binds the channel receptor
-channel opens (gating) to allow ions to cross membrane

Question 5

ions

Answer 5

Na+, K+ Ca2+

Question 6

LGIC extracelllular domain

Answer 6

binds first messenger

Question 7

LGIC transmembrane domain

Answer 7

pore through which ions flow

Question 8

LGIC in neuronal signaling

Answer 8

-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

Question 9

LGIC first messengers

Answer 9

-serotonin
-y-aminobutyric acid (GABA)
-nicotinic acetylcholine
-glutamate
-glycine

Question 10

LGIC clinical relevance

Answer 10

-site at which anaesthetic agents act
-involved in BP regulation and cardiovascular disease

Question 11

Nicotinic acetylcholine receptor

Answer 11

-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

Question 12

Receptor tyrosine kinases

Answer 12

-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

Question 13

kinases examples

Answer 13

-insulin receptor
-growth factor receptors (epidermal, platelet-derived)

Question 14

Kinase receptors

Answer 14

-many families
-various EC domains
-cell growth
-dysfunction=cancer

Question 15

Besides receptor internalization, another way to terminate the signaling from receptor tyrosine kinases could be:

Answer 15

protein phosphatase as part of a protein phosphorylation cycle

Question 16

Ras/MAP kinase signal cascade

Answer 16

-growth factor receptor binds growth factor ligand and initiates mitogen-activated protein kinase (MAP kinase) cascade

Question 17

Ras/MAP kinase signal cascade mech

Answer 17

-activated Ras binds and activates MAP3K which triggers cascade
-SLIDE 9-10 pic

Question 18

Activation of G-protein Ras

Answer 18

-molecular switch to activate cell proliferation, migration, transformation, survival
-signal activation involves: adaptor protein (Grb2) and GEF (Sos)

Question 19

Ras mutations

Answer 19

-permanent activation of Ras enzyme
-big in pancreatic cancer
-HRas, KRas, NRas
-meds lacking

Question 20

Activated Ras effectors

Answer 20

-PLCe
-RalGDS
-Raf
-PI3K

-so many and so many pathways = very problematic

Question 21

KRAS structure

Answer 21

-hypervariable region (HVR)
-G domain
-active when GTP bound
-inactive when GDP bound

Question 22

hypervariable region

Answer 22

-localization to membrane

Question 23

G-domain

Answer 23

-switch I and II
-P-loop
-slide 12 pic

Question 24

activation of KRAS

Answer 24

when GTP bound

Question 25

inactivation of KRAS

Answer 25

when GDP bound

Question 26

Ras

Answer 26

-membrane bound -monomeric G protein -activated by GF or by T cell receptors

Question 27

P loop

Answer 27

changes here cause most cancer

Question 28

Switch

Answer 28

-conformation of 2 loops based on GTP or GDP bound

Question 29

Active Ras

Answer 29

-GTP bound -binds specific effectors -activates multiple pathways

Question 30

Hydrolysis of GTP to GDP

Answer 30

-GTP to GDP -rate increased by GTPase-activating proteins (GAP)

Question 31

Guanine nucleotide exchange factors (GEF)

Answer 31

-increase GDP dissociation -slow hydrolysis -prolong activation of Ras -promotes cancer

Question 32

Slide 14

Answer 32

slide 14

Question 33

Mutations KRAS

Answer 33

-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

Question 34

KRAS inhibition

Answer 34

-very difficult -very high affinity for GTP and GDP -mutant structure binds GTP with increased affinity -constitutively active

Question 35

Target G12C KRAS mutant

Answer 35

-irreversible inhibitor -allosteric pocket in switch II -lead compound that covalently links to C12 -covalently bound inhibitor prevents GTP binding

Question 36

G-protein-coupled receptors (GPCRs)

Answer 36

-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

Question 37

GPCR structure

Answer 37

-7 a-helical transmembrane regions -conformational change upon receiving signal

Question 38

G-protein cycle (trimeric G protein)

Answer 38

-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

Question 39

Desensitization

Answer 39

phosphorylation of GPCR residues in THIS region by kinase SLIDE 19

Question 40

SLIDE 19

Answer 40

SLIDE 19

Question 41

Heterotrimeric G-proteins that couple to GPCRs

Answer 41

-3 subunits Ga, GB, Gy -association with agonist-bound GPCR induces dissociation of GDP and GTP binding

Question 42

Ga

Answer 42

-GTPase activity -20 subtypes -dissociates from By complex and stimulates/represses effector protein when activated