Signal Transduction Flashcards

Question

Answer 1

Discriminator domain -tells what ligand it is effector domain -part which transduces the signal -many divergent ways transition btwn inactive and active frequently an example of allosteric regulation (most?) receptors found in inactive conformation when no ligand present if it is active without ligand then problems

Answer 2

ligands which stabilise the inactive conformation

Answer 3

the actual signal stabilises the receptor's active conformation

Answer 4

some have intrinsic enzymatic activity involved in signalling the others that do not instead co-opt other proteins with enzymatic activity to signal

Answer 5

-large class of receptors that are coupled with G-protein -receptor kinases, RKs: >more ancient serine/threonine >Receptor tyrosine kinases found in animals (higher eukaryotes)

Answer 6

many different types no clear classification -ion channel coupled receptors -Adhesion (ECM) sensing (includes integrins)

Answer 7

includes steroid hormone receptors. Are often transcription factors

Answer 8

either: -ligand activated -ligand inhibited Monomeric proteins consisting of two domains -DNA motif recognition domain -signal binding domain

Answer 9

require ligand to dimerise from monomers in cytoplasm -requires sufficient signalling molecule conc inside cell -due to symmetric nature of dimer - needs to bind divergent identical sequences that are palindromic on the DNA -can be activators or inhibitors of transcription -need to bind ligand to dimerise -need to dimerise to bind DNA eg TraR: bacterial quorum sensing TF:

Answer 10

opposite of ligand activated ones -structurally similar to activated ones -DNA binding motif -ligand binding motif -form stable dimer in absence of ligand eg TetR Tetracycline binds receptor dimer doesnt dissociate but loses DNA affinity when bound to ligand

Answer 11

nuclear receptors DNA binding motif ligand binding motif sense small molecules that penetrate membrane -Steroid hormones: >cortisol >retinoic acid >thyroxine principle similar to bacteria BUT can be Monomeric OR Dimeric also can coopt a lot of coactivators and coinhibitors - form complexes w other TFs in eukaryotic nucleus

Answer 12

Based on serine threonine receptor kinases sense important growth horomones that are also important morphogens

Answer 13

Large protein Dimer 2 identical subunits - antiparallel dimer

Answer 14

Class II: Constitutively active TM kinases -Recognise the antiparallel dimer ligand -2 Type II receptors bind across the ligand -now have affinity to recruit the Type I receptor -enables protein-protein interaction btwn type I and II receptors -Type II is constitutively active kinase that phosphorylates and activates Type I

Answer 15

Type I receptor is the Effector part of receptor complex responsible for further signalling SMADs -recognise phosphorylated type I receptor -the phosphorylation allows them to bind type I -Type I phosphoryaltes SMAD on c terminal tail (2 serines) -changes SMAD conformation, comes off receptor complex

Answer 16

after phosphorylation by Type I receptor and coming off the receptor complex: -3 SMADs to form signalling complex -phosphorylation allows them to assemble assemble into heterotrimer: -2 SMADs -1 CoSMAD heterotrimer exposes on its surface a nuclear localisation signal -imported -in nucleus it can bind resident TFs and influence gene expression

Answer 17

phosphatases in the nucleus remove the phosphate from SMADs individual SMAD monomers exported out of nucleus this process of SMAD activation - nucleus - phosphatase - export cycles as long as there is signalling from receptor phosphatase disassembles all the SMAD complexes eventually when signalling stops

Answer 18

important factor in signalling -receptors in eg class II system are clustered by binding the ligand -this complex is endocytosed by clathrin coated pits: -pathway where complexes signal and receptors get recycled back to PM -maintains sensitivity by continuously recycling receptors by Caveolin pathway: -receptors endocytosed -go to degradation pathway -cell can downregulate signalling by removing receptors into degradation pathway -drops sensitivity to ligand (adaptation)

Answer 19

evolutionarily novel large extracellular domain involved in ligand sensing: -discriminator beneath membrane is kinase domain: -tyrosine kinase -C terminal tail has role in signalling

Answer 20

though to not be present at first idea that binding ligand brough kinase domains of two receptors close enough to cross-phosphorylate but this is not true even tho both kinases are identical -one serves as allosteric regulator of other -only one gets kinase activity activated -then this Kinase phosphorylates BOTH c terminal tails to activate receptors -Each pY on these tails is a binding slot for a protein with an SH2 domain allows complex to grow and grow creating almost a solid phase of protein underneath membrane that connect individual receptors through multivalent binders

Answer 21

soluble cytoplasmic proteins can still interact w PM eg SFK - Src Family Kinases viral protein co-opted for cellular use

Answer 22

SH1: Tyrosine kinase domain SH2: Binds phosphorylated Tyrosine SH3: Binds PXXP kink strucrture SH4: N-terminal lipidated fragment allowing binding to PM

Answer 23

Tyrosine residue at C terminal domain phosphorylated in inactive form SH2 domain loops back to bind this puts protein in "latched" closed conformation closing in on itself inhibiting the phosphorylation this c terminal phosphate needs to be removed to activate Src kinase activity this allows protein to open up SH2 and SH3 domains can also find external ligands now (SH2 - pY, SH2 - PXXP) complex stage wise activation process which eventually leads to phosphorylation at activation loop of kinase Src plays big role in signalling of many receptors

Answer 24

Phosphorylate C terminal tail dephosphorylate activation loop let molecule fold back in on itself and diffuse back into cytoplasm

Answer 25

Src kinase -SH2 and SH3 domains -recognise pY in on RTK and contribute to phosphorylating other proteins in vicinity ZAP70 -similar organisation kinase -2 SH2 domains, can bind 2 pY residues -carries tyrosine kinase so can contribute to making more pY in the complex Grb2 -scaffold -has SH2 and SH3 domains PI3 kinase: -lipid kinase -generates PIP3 - a second messenger (adds another phosphate to PIP2

Answer 26

lipid kinase generates PIP3 second messenger from PIP2 is a complex of 2 diff proteins >P110 -catalytic >P85 - regulatorty if this complex is not bound to pY then the regulatory subunit inhibits the caralytic one inhibited conformation 2 SH2 domains - binding pY on c terminal tails of RTK: de inhibits the catalytic subunit can start generating PIP3 lipid connects RTK signalling to 2nd messenger PIP3 generation

Answer 27

eg cytokine receptors (erythropoietin receptor eg) looks similar to RTK -EC discriminator -TM region -C terminal tail that can be phosphorylated 1st part of complex activation is different requires specific class of non-receptor TKs that recognise active bound receptors (allosteric regulation :0) These kinases are JAKs recognise active receptor bind it they themselves are allosterically activated by this then similar to RTK activated JAKs can phosphorylate C-terminal tails generate lots of pY proteins eg Src can bind

Answer 28

requires signal transducer: STATs also are transcription activators has SH2 domain binds pY on receptors C terminal tail STAT is phosphorylated by JAKs unbinds C terminal tail two STAT subunits complex by binding each others' pY with their SH2 domain -dimerisation exposes their nuclear localisation signal -go to nucleus -then are disassembled by phosphatase in the nucleus -in some cases: after the STATs are dephosphorylated the nuclear localisation signal becomes an export signal, exported by CRM1 protein cycling continues as long as receptor active

Answer 29

Fast negative feedback: -cytoplasmic tyrosine phosphatases (SHP1/2) -recruited into signalling complex -while the ligand is present activation prevails over inactivation -overall signalling of complex -once signal is removed -phosphatases prevail, quickly remove phosphate from the pY residues -signalling complex disassembles in seconds

Answer 30

requires change in gene expression (transcription and translation takes time) phosphorylated STATs transcriptional target is a molecule called SOCs has SH2 domain and a domain that recruits SOC to signalling complex ubiquitinates complex resulting in endocytosis of receptors and depletion of signal

Answer 31

sense adhesion of cells to environment -integrin binds ECM -alpha and beta integrins -different kinds in each class so can generate diff dimer combos normally in inactive conformation folded over inside out signalling and outside in signalling

Answer 32

cell making itself adhesive to environment ECM on request eg leukocytes sensing signal from inflammation site activates integrins

Answer 33

eg talin, kindlin, vinculin adapters between cytoskeleton and c terminal tails of integrin receptors integrin opens up and can now grab ECM also causes them to cluster on cell surface eg focal adhesions

Answer 34

integrins have no tyrosine kinase domains require help of non receptor tyrosine kinases -Src kinase -Focal adhesion kinase different mechanisms of engaging them based on integrin class but idea is same activated integrins clustering results in formation of bound kinases which cross phosphorylate due to being at high density

Answer 35

Ras small GTPases can bind GTP - use as fuel for work involved in allosteric regulation have switch I and II mobile elements position of these elements depends on if bound to GTP or GDP

Answer 36

nucleotide cycles active when bound to GTP can bind effectors that they activate effectors have high affinity for GTP form low for GDP form GEFs and GAPs activate and deactivate them

Answer 37

G protein exchange factors stabilise free of nucleotide conformation and release GDP GTP can then bind to nucleotide free state and releases the GEF

Answer 38

G protein deactivators activate hydrolysis of GTP by the GTPase

Answer 39

GDP dissociation inhibitors certain families of GTPases possess them proteins that transport the GTPases through the cytoplasm through various membrane compartments

Answer 40

Gamma phosphate of GTP stabilises interactions with G protein folds in switch I and II GAP has arginine residues with +ve charge force open switches now H2O can get in and hydrolysis of GTP is sped up 1000x from GTP on its own Gamma phosphate removed from GTP -> GDP causes inactive conformation -switches open up due to no negative charge from phosphate group -conformation no longer recognised by effectors GEF can bind residues open up the switches - allosteric regulation lets GDP unbind from protein -lots of GTP in cytoplasm much 10x GDP conc -GTP much more likely to come in and bind -Grabs the switches and pulls them back in -G protein no linger has affinity for GEF back to beginning of cycle

Answer 41

GTPases play 2 roles -recruit effectors - GTPases usually membrane bound so bring enriches effectors from cytoplasm to membrane -providing biological work for the reaction -enzymes -scaffolds

Answer 42

inactive scaffold conformation only has one open site for GTPase small GTPase binds in active form allosteric regulation of scaffold effector can now bind its interaction partners (eg kinases in cascades) GTPase allows the chemical reaction on the scaffold to take place

Answer 43

most of them are functional as membrane proteins except Ran -- plamitoylated (ingolgi) = reversible -- prenylated = permanent increase strength of interaction with membrane - can no longer dissociate from it are packed in vesicles transported to PM on cytoskeleton GTPases end up on PM activated here by upstream receptors at enzyme there is enzyme that cleaves Palmitoyl - allows dissolving into cytoplasm can float around until reach golgi again cycles

Answer 44

Heterotrimeric complexes 3 subunits Alpha - Binds and hydrolyses GTP Beta - one large fold - tangled up with small peptide: the Gamma subunit beta and gamma assembled at time of protein translation - unbreakable interaction until they are both disassembled together later on Alpha and gamma attached directly to membrane relationship with beta subunit is more dynamic coupled to receptors receptors play the role of GEFs for Small GTPases they activate the Alpha subunit

Answer 45

assembled as trimer when inactive alpha sub is bound to GDP high affinity of alpha for beta/gamma receptor activation: -receptor acts like GEF -widens GTPase domain cleft -GDP falls out -GTP now binds (10x GDP conc) -3 things happen when EC signal binds receptor: >exchange of nucleotide in G-alpha subunit >as a result - Beta/gamma and G-alpha subunit complex breaks up >both dissociate from receptor active G alpha and Beta/gamma subunits can signal by binding partners but only G-alpha has GTPase activity - can provide work

Answer 46

RGS proteins - Regulators of G-protein Signalling have affinity for large G-proteins help them hydrolyse GTP quickly once inactivated - reverse process -inactive G-alpha rebinds beta/gamma -rebind receptor (alpha only bit that interacts w it)

Answer 47

7 pass strand membrane proteins 7 alpha helices incorporated into PM 3 loops in extracellular part 3 loops intracellular N terminus - V diverse - usuallly EC C teminus - IC G proteins bind the intracellular loops interact w G-alpha subunit

Answer 48

either at N terminus or with the EC loops or woth the alpha helices alpha helices conformational change key part of transmitting signal C terminal tail can be phosphorylated to interact with signalling molecules

Answer 49

eg opioid receptor Binding pocket for ligand ligand sinks into hole btwn alpha receptors causes conformational change have 100s conformations - varying levels of activity GPCRs unusual as can have base level of activity without ligand binding ligand binding increases or decreases this agonist - high binding ligand - activity goes higher -partial agonists dont activate as much - usually pharmaceuticals - real molecule is full agonist inverse agonist shuts down the basal activity

Answer 50

Rhodopsin GPCR detects photons has no chemical ligands -Retinal is bound already -2 conformations of Retinal >Cis - arms folded >Trans - Arms open Photon absorbed by Cis-retinal changes conformation to trans-retinal physically pushes on alpha helix transfers conformational change to GPCR a-helices -activates G protein Transducin -active transducin activates cGMP phosphodiesterase -which hydrolyses the cGMP in the cell -causes cGMP activated ion channels to stop working -causes membrane hyperpolarisation -initiates nervous pulse

Answer 51

Variety of G-alpha subunits defines it 960 combinations of alpha, beta, gamma from different isoforms Gs - adenyl cyclase activator Gi - adenyl cyclase inhibitor Gq,11 - activates PLC-Beta G12,13 - activate signalling via RhoA - specifically function upstream of small GTPases, in active conformation recruit GEFs for them - causes cascade of action

Answer 52

integration of many signals provides additional flexibility eg adenyl cyclase generates cGMP from GTP Gs-alpha subunits act upstream of it (from receptors receiving stimulatory hormones) activates adenyl cyclase inhibitory pathways activated by other hormones compete for activation/inhibition of adenyl cyclase integrates many signals into one response

Answer 53

intracellular signalling molecules of a non-protein nature most are made intracellularly and are then free to diffuse in cytoplasm (hydrophilic) or in the membrane (hydrophobic)

Answer 54

gases - NO, CO2 H2S reactove oxygen species ROI Ca2+ ion !! cyclic nucleotides !! inositol triphosphate !!

Answer 55

diffuse in membrane (PM, Golgi) glycerol phosphotidic acids phosphoinositides

Answer 56

Sphygnolipids Glycerophospholipids

Answer 57

processed from Sphygnomyelin Sphygnoid base 2 lipid tails Has positive choline attached to negative phosphate at head

Answer 58

Sphygnomyelinase (a signalling enzyme) processes sphygnomyelin to remove the phosphocholine ceramide molecule remains -precursor for two diff signalling molecules >tail at bottom: Arachidonic acid, precursor for others >Sphignosine - poor affinity for lipid bilayer, is phosphorylated by sphignosine kinase to make Sphignosine-1-Pi (soluble in cytoplasm), so can diffuse between and within cells

Answer 59

Phosphatidic acid - range of effectors, negative charge diaglycerol - basic part of Phospholipids, can be dephosphorylated/phosphoryolated neutral charge - binds and activates protein kinase C

Answer 60

generates 8 v important lipids (phosphoinositides) produced out of Phosphatidylinositol by sequential PI kinase and phosphate action

Answer 61

strongly negatively charged lipids eg PIP = -3 PIP2 = -4 PIP3 = -5 nonspecifically interact v strongly and non-specifically with positively charged proteins esp with lipid binding domains many actin polymerisation regulator proteins recognise them in the membrane and bind them

Answer 62

Glycerol as base of lipid 3C with 3 OH groups all 3 OH attached to something -2 with carboxylic acids -other one with a phosphate - importanf for connecting glycerol to head group Head group is a sugar, inositol -- carbons are numbered -- C number one is attached to the phosphate -- 23456 around rest of ring -- different numbered carbons (3 4 or 5) phosphorylated to give diff Phosphotidylinsoitol eg phosphorylate carbon 3 - PI3P then carbon 5 to give - PI3,5P2 continuous flux of these molecules being modified into different ones by phosphorylation/phosphatases

Answer 63

the most important 3 diff ones PI3,4P2 PI3,5P2 PI4,5P2 produced in small bursts

Answer 64

PI3,4,5P3 produced in small bursts by Phosphatidylinositol triphosphate kinase (PI3 kinase - important with RTKs) binds and is involved in activation of PKB kinase important for cell survival deregulation of this signal resuslts in cancer cells quickly degraded by P10 phosphatases

Answer 65

some G-protein effectors are phospholipases chop off the phosphatidylinositol phosphates several classes PLA (Phosphatidyl lipase A) chops off the tails of the glycerol' liberates the arachidonic acid making it a freely diffusible signalling molecule PLC chops the phosphate off the glycerol releases the inositol sugar bound to the phosphates a biphosphate would release inositol sugar with 3 phosphates -- results in IP3, v important signalling molecule as it activates calcium channels in ER and releases calcium from ER -- connects extracellular signals to release of intracellular calcium from ER

Answer 66

Inorganic ion cell cannoth create or destroy it can only manipulate by sequestration/release Ca2+ is very naturally abindant conc in environment - 1mM cytoplasmic Ca2+ only 100nM (10,000x less) -cells spend lots of energy pumping Ca2+ out -no energy required for influx, just open channels

Answer 67

in 2 types of organelle >the ER, 0.1-1mM large conc gradient w cytoplasm >mitochondria can store higher conc than extracellular environment, 10mM

Answer 68

extracellular stimulus on PM receptor activates Phospholipase C PLC -PLC processes phosphatidylinositol lipids -releases Inositol triphosphate IP3 signalling molecule -This opens Ca2+ channel -Ca2+ floods cytoplasm >low Ca2+ cellular conc - activates channels >high Ca2+ cellular conc - inhibits channels >excitable system - add a little - increases release even more >then later they close down Biphasic dynamics creating a wave of Ca2+ propagating in the cell either: >small flashes >or complex wave patterns causes quick violent reaction from cell Ca2+ con decreases from active pumping out of Ca2+ (to mitochondria, extracellular, ER)-

Answer 69

Ca2+ is toxic to cell if too much in cytoplasm for too long because it activates so many signalling molecules also activates ancient response of ocean cells for breaking of the PM -activates PM healing response in cells

Answer 70

By Calmodulin main Ca2+ sensor Ca2+ binds to the EF-hand motif via negative charged residues EF-hand can coordinate many Ca2+ ions (up to 4) one EF-hand on each end of Calmodulin responds to changing Ca2+ conc via allosteric regulation 2 diff spatial conformations Ca2+ binds changes Calmodulin conformation then can bind other proteins that have an IQ motif/domain that affects conformation of downstream protein

Answer 71

Ca2+ floods into cell binds calmodulin calmodulin wraps around IQ motifs in GEF GEF then changes to bind PM where they activate Ras GTPase

Answer 72

All Ca2+ channels autoregulated by Ca2+ PM channel has calmodulin near it -channel opens -Ca2+ floods in from EC environment -immediately binds calmodulin molecules nearby -Bound calmodulin binds the channel and causes it to close -only lets the channel signal for ~1sec -around 1million ions let in fast negative feedback on channel

Answer 73

Receptor operated -respond to Extracellular agonist ligand (eg neurotransmitters) cyclic nucleotides -second messenger operated allows cell to let in calcium based on intracellular activity machinery for complex feedback loops voltage operated -voltage across membrane generates pulse stretch activated mechanosensory channels Piazza 1 and 2 -like bath plug -bent in a way -membrane stretches -their conformation changes to open up -lets Ca in allows cell to sense mechanical tension in PM Ca release activated channels CRACs -Ca in ER drops -RI sensor protein -forms membrane binding cluster -interacts w Steam channnels -steam/RI permits input of calcicum in response to Ca depletion in ER

Answer 74

Calmodulin kinase Calcineurin Phosphatase - PP2B

Answer 75

Shuriken structure 2 hexamer layers of molecules 6 upper 6 lower 12 kinase domains overall all independent - no cooperativity all are autoinhibited : -locked on something that resembles substrate but cannot be acted on so is stuck -IQ motif on each kinase -calmodulin binds it -deinhibits -kinase unfolds and can perform phosphorylation to activate neighbour domains -other proteins dephosphorylate activation loop and inactivate kinase domains again

Answer 76

can sense the frequency of the Ca2+ signal pulses infrequent pulses activate fewer kinase domains (1-2) more frequent pulses cause the kinase to keep activating -every new pulse allows a new kinase domain to open up -activity of the kinase grows proportionally to eg frequency of neural pulses allowing info processing in neuron cells

Answer 77

Heterodimer 2 peptides - A and B subunit autoinhibited in signal absence B subunit binds Ca directly via EF-hand motifs A subunit has flexible domain called the B subunit binding helix

Answer 78

under normal circumstances A subunit bound to B subunit via the B subunit binding helix in Ca2+ presence Calmodulin wraps around the helix and prevents it from binding B subunit activation of this phosphatase requires both directly binding Ca2+ and binding Ca bound calmodulin

Answer 79

cAMP - organic molecule signalling done by rapid generation and degradation of the molecule generated by adenyl cyclase family of proteins

Answer 80

by adenyl cyclase proteins take molecule of ATP hydrolyse the beta and gamma phosphates together as a pyrophosphate remaining alpha phosphate ends up bound to 2 groups on the same sugar creating cyclic molecule

Answer 81

by phosphodiesterases many of them present in cell on lookout for cAMP gives v short range of cAMP signalling gives v sharp spatial maxima if inhibit phosphodiesterases - whole cell floods with cAMP makes it useless for signalling by giving uniform distribution

Answer 82

only know 3 nucleotide gated Ca2+ channels protein Kinase A GEF Epac - cAMP binding changes conformation so that it can bind Rab GTPase

Answer 83

PKA heterotrimer 2 kinase domains - catalytic sububits dimer of regulatory subunits each reg subunit has 2 cAMP binding slots when cAMP binds allosteric regulation makes them release the catalytic kinase domains as free floating molecules cAMP molecules in fast equilibrium with regulatory site binding so cAMP degradation in cytoplasm by phosphodiesterases: -causes conforation of regulatory subunits to change back so that catalytic subunits are sequestered again

Answer 84

Mitogen activated protein kinases

Answer 85

consist of 3 kinases that sequentially activate each other via phosphorylation MAP3K - Serine/Threonine MAP2K - Double specificity: Tyrosine and Serine/threonine MAPK - usually the effector - goes to nucleus and phosphorylates targets cascade used for signalling

Answer 86

by a variety of input signals controlled by various pathways including: -receptors -small GTPases -G-proteins... all MAP3K require activation by an upstream kinase sometimes called MAP4K BUT these ones belong to all sorts of classes of kinase so not so consistent to call them that

Answer 87

needs both a serine and threonine phosphorylation sites near each other on activation loop

Answer 88

each phosphorylation step in the cascade is opposed by phosphatases without the opposition o phosphatases the cascade would flare up one time and stay up all the time - useless for signalling

Answer 89

-MAPK phosphorylated by upstream kinases -detaches from the cascade (suggests some allosteric regulation - change in affinity for scaffold proteins) MAPK can phosphorylate cytoplasmic targets eg p90 RSK but generally signal by being imported into nucleus >have no DNA binding domain >but instead phosphorylate resident factors >can do this via parallel pathways: activates two diff factors that work together to bind DNA and change gene expression

Answer 90

in budding yeast a produces chemoattractant for alpha binds GPCR receptor: -beta/gamma subunit of G-protein signals -active b/g subunit binds and recruits scaffold from cytoplasm - Ste5 -recruits the three MAPKs: >Ste11 -MAP3K >Ste7 -MAP2K >Fus3 -MAPK effector >phosphorylates Ste12 TF MAP4K initiator is Ste20 - phosphorylates Ste11 Ste20 activated by small GTPase Cdc42 Fus3 inhibits Tec1 binding to Ste12 in filamentous growth pathway

Answer 91

thought before that MAPKs phosphorylated each other in cytoplasm but in reality it occurs on scaffold that recruits necessary components and enriches them near receptor scaffold originally thought to be one big protein that combines all the components together like a holder -keeps them on the same structure so changes dynamics as no longer need to randomly bump into each other however Ste5 (and other scaffolds) operate a bit differently: -Ste7 MAP2K already coupled w Ste5 scaffold -Fus3 (MAPK) is allosterically activated by Ste5 scaffold, its activation loop is revealed upon binding Ste5, allows access by Ste7 (MAP2K) -phosphorylated Fus3 then released to nucleus basically - all kinases dont simultaneously bind the scaffold

Answer 92

1. Pheromone pathway (Ste/Fus stuff) 2. Filamentous growth pathway

Answer 93

non sexual growth doesnt result in fusion instead produces protrusion that grows like Hypha (isnt one tho) -shares elements w pheromone pathway -difference is whether or not Ste5 (scaffold) is present -Ste20 activated by Cdc42 small GTPase in both pathways -filamentous growth pathway skips Ste5 -activates ONLY Kss1 protein (pheromone pathway activates both Fus3 and Kss1 MAPKs) -because Fus3 requires binding to Ste5 to reveal activation loop for phosphorylation by Ste7 -changes Kss1 activity (also no Fus3 direct activity present either) -so get different response reuse of proteoins in diff context to give diff response

Answer 94

High osmolarity response cell wall integrity response

Answer 95

Sensors between cell membrane and cell wall -Hypertonic stress (eg salinity increase from drying puddle) -cess sense change in turgor pressure from water leaving cell, cell shrinking - sense mechanical change -activates Cdc42 -activates Ste20 (MAP4K) -This time Pbs2 protein is activated: is the MAP2K and Scaffold: -Cdc42 -then Ste20 MAP4K -Ste11 MAP3k -Pbs2 Scaffold + MAP2K -Activates Hog1 MAPK, activating its many nuclear factor targets HOG pathway

Answer 96

Sensors also betwenn membrane and wall -Rho1 small GTPase activated -an effector is Pkc1 -the MAP4K -MAP3,2,1Ks actiavted -MAPK activates factors that stop budding growth because as bud grows cell wall synth hasnt caught up fully - so is weaker at bud -pathway acts as frrdback in normal growth so it doesnt break the wall -can also act to stop cell cycle under stress

Answer 97

kinases at each step able to be replaced by diff homologues many kinases can do same step diff combos of kinases to make pathways many of these cascades require input from small GTPase the MAP4K is the effector of the small GTPase

Answer 98

mitogenic signals/growth factors eg the ERK pathway can be involved in cancers so many drug targets within

Answer 99

growth factor receptor is an RTK dimerises when ligand binds -Adapter Grb2 has SH2 domains binding the C-terminal pY residues on the RTK dimer -this adapter binds mSOS - a Ras GEF -causes Ras to be activated on the PM down stream of the Grb2/mSOS complex -Ras recruits the MAP3K - RAF -the MAP4K PAK2 is recruited by Rac, another GTPase many scaffolds involved MP1 scaffold holds MEK1 (MAP2K?) then MAPK ERK1 - has many targets in nucleus and on nuclear membrane activates early respnse genes

Answer 100

dysregulated in cancer can try to target RAF(MAP3K) or Ras GTPase Ras cant take small molecule inhibitors so instead artificially target it for degradation

Answer 101

why not just have one kinase autoamplifying scaffolds exist so not just a bunch of amplification in cytoplasm instead having 3 kinases allows having a Non-linear response: -eg Michaelis menten - describes a system where response is linear until a certain point -If the Hill coefficient is >1 then response begins to look more non-linear -as n gets bigger - more extreme non linear -basically sets a threshold after which activity jumps on a lot -allows the system to not respond to the small background noise in the simulus (as it would a small amount if response was linear proportionally) Will only give response after a significant stimulus threshold has been passed hill coefficient in MAPK pathway could be ~5

Answer 102

dynamics of the cascade shaped by feedback loops system has fast positive feedback for activation sharp rise followed by slower negative feedback for a drop back to pre-stimulus levels -called PERFECT ADAPTATION

Answer 103

Positive feedback helps to provide fast and strong activation many mechansims phosphatases that inactivate the kinase targets are found already bound to the MAPK protecting it from noise signal but activated MAPK phosphorylates the phosphatase and removes it since the inhibitor is removed - MAPK activity can go up MAPK also activates a GEF that gives the Small GTPases in teh response more GTPase activity

Answer 104

MAPK slowly phosphorylates other components of cascade incl. the scaffold protein After MAPK actovoty grows too high it disassembles the complex back down until the phosphatases have time to remove the phosphorylations so complex can reassemble for more activation

Answer 105

using the principles of MAPK cascades it is possible to control behaviour of signal transduction pathways at will: experimental example: -yeast pheromone pathway modified to encode Ste5 with a sticky bit and also additional proteins whose expression was controlled by Ste12 as either negative regulators (phosphatases with binding domain for the Ste5 sticky bit) or another version positive regulators (Ste50 with a binding domain) these experiments demonstrated that the pathway with additional feedback loop demonstrated Hill coefficient 2.4 vs 1.2 for the WT cascade

Signal Transduction Flashcards

(130 cards)