Cell Signalling - Chapter 15 PDF

Cell signalling - Chapter 15 Prof. Dr. Anika Nagelkerke 01-10-2024 🤯 TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-depend...

Cell signalling - Chapter 15 Prof. Dr. Anika Nagelkerke 01-10-2024 🤯 TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview 🤔 EXTRACELLULAR ENVIRONMENT INTRACELLULAR ENVIRONMENT WHAT IS HAPPENING CELLULAR RESPONSE INSIDE AND OUTSIDE? INTRACELLULAR ENVIRONMENT CHANGES EXTRACELLULAR ENVIRONMENT CHANGES 🤓 extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 SELF STUDY - know and understand this terminology: EXTRACELLULAR SIGNAL MOLECULE (a.k.a. ligand): Secreted or surface- bound chemical signal that binds to a receptor and regulates cell activity. Can be a protein, small peptide, amino acid, nucleotide, steroid, retinoid, fatty acid derivative, and even a dissolved gas (e.g. nitric oxide and carbon monoxide). RECEPTOR: Protein that binds a specific signal molecule (ligand) and initiates a cellular response. Some are on the cell surface, others are inside the cell. INTRACELLULAR SIGNALLING MOLECULES: Enzymes and small molecules that relay the signal from the receptor to the effector protein. EFFECTOR PROTEINS: The final targets of the signalling pathway. They are altered by the signal and execute the response of the cell. SIGNAL TRANSDUCTION PATHWAY: A chain of reactions by which signals from the cell surface are transmitted to a variety of intracellular targets.  EXAM(PLE) QUESTION You are asked to put the following items in the right order, from first in the sequence to last. Which one is correct? I. intracellular signalling molecules II. receptor protein III. effector proteins IV. extracellular signal molecule V. cellular response a. IV - II - I - III - V. b. V - I - IV - II - III. c. IV - I - II - III - V. d. II - I - III - V – IV.  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 🤔 RESPONSE TO AN EXTRACELLULAR SIGNAL CAN BE SLOW OR RAPID extracellular signal molecule intracellular cell-surface signalling pathway receptor protein nucleus FAST DNA ALTERED SLOW (less than a PROTEIN RNA (minutes to second to FUNCTION hours) minutes) ALTERED PROTEIN SYNTHESIS plasma membrane ALTERED CYTOPLASMIC MACHINERY ALTERED CELL BEHAVIOUR see also figure 15-14  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling proteins effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling proteins n s t e ps? act i vat io A ll NO! effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 🤔 MOST SIGNALLING PATHWAYS CONTAIN INHIBITORY STEPS inactive transcription regulator protein P kinase inhibitor protein GENE EXPRESSION see also figure 15-9  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview 🤔 POSITIVE AND NEGATIVE FEEDBACK LOOPS stimulus A B + B acts back to increase the activity of A positive feedback stimulus C D - D acts back to decrease the activity of C negative feedback see also figure 15-18 🤔 POSITIVE AND NEGATIVE FEEDBACK LOOPS  EXAM(PLE) QUESTION Consider the following pathway: A Which of the following represents negative feedback? a. A. b. B. B III c. I. I II d. II and III. C  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 ONLY ONE AT A TIME?! extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling proteins effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 🤔 INTEGRATION OF MULTIPLE EXTRACELLULAR SIGNALS A B SURVIVE C A GROW & DIVIDE B C E D A DIFFERENTIATE B C G F I apoptotic cell (more on this in chapter 18) J DIE K see also figure 15-4  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 ONLY ONE OUTCOME PER SIGNAL?! extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 🤔 ONE SIGNAL, MULTIPLE OUTCOMES (CELL TYPE-DEPENDENT) CH3 O H3C N+ O CH3 H3C Acetylcholine heart pacemaker cell salivary gland cell skeletal muscle cell acetylcholine receptor protein DECREASED RATE OF FIRING SECRETION CONTRACTION see also figure 15-5  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 🤓 TWO CLASSES OF RECEPTORS CELL SURFACE RECEPTORS INTRACELLULAR RECEPTORS plasma membrane small, hydrophobic signal molecule cell-surface receptor protein target cell carrier protein hydrophilic signal intracellular receptor protein nucleus molecule target cell see also figure 15-3 🤓 TWO CLASSES OF RECEPTORS INTRACELLULAR RECEPTORS nucleus DNA receptor-binding element TRANSCRIPTION OF TARGET GENE Take a look at Figure 15-65 for examples of extracellular signals - STEROIDS! (small and hydrophobic)  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview 🤓 CONTACT DEPENDENT PARACRINE signalling cell signalling cell target cell target cells soluble signal membrane-bound receptor protein molecule signal molecule (local mediator) endocrine cell SYNAPTIC ENDOCRINE target cell synapse soluble signal cell body molecule (hormone) axon soluble signal molecule target cell neuron blood stream (neurotransmitter) target cell see also figure 15-2  AUTO CONTACT DEPENDENT PARACRINE signalling cell target cell signalling & target cell soluble signal membrane-bound receptor protein molecule signal molecule (local mediator) see also figure 15-2 SELF STUDY - know and understand this terminology: CONTACT-DEPENDENT SIGNALLING: Form of intercellular signalling in which signal molecules remain bound to the surface of the signalling cell and influence only cells that contact it. PARACRINE SIGNALLING: Short-range cell-cell communication via secreted signal molecules that act on neighbouring cells. The signalling molecule is released into the extracellular space and influences target cells in close proximity via a specific protein receptor. AUTOCRINE SIGNALLING: Short-range cell-cell communication via secreted signal molecules where the signalling cell is also the target cell. NEUROTRANSMITTER: Small signal molecule secreted by the pre-synaptic nerve cell at a chemical synapse to relay the signal to the postsynaptic cell. Examples include acetylcholine, glutamate, GABA, glycine and many neuropeptides. SELF STUDY - know and understand this terminology: SYNAPTIC SIGNALLING: Intercellular signalling performed by neurons that transmit signals electrically along their axons and release neurotransmitters at synapses, which are often located far away from the neuronal cell body. Signal transduction from neuron to neuron, or neuron to effector cell (muscle, secretory, …). ENDOCRINE CELL: Specialised animal cell that secretes a hormone into the blood. Usually part of a gland, such as the thyroid or pituitary gland. HORMONE: Signal molecule secreted by an endocrine cell into the bloodstream, which can then carry the signal to distant target cells. ENDOCRINE SIGNALLING: Long range cell-cell communication where the signal molecules (hormones) are secreted by specialized endocrine cells. The signal molecules are carried through the circulation to act on target cells at distant body sites. The response is often relatively slow. Examples include insulin signalling.  EXAM(PLE) QUESTION Consider the following signalling pathway: This is an example of? a. contact-dependent signalling b. paracrine signalling c. synaptic signalling d. endocrine signalling  EXAM(PLE) QUESTION Some tumours can produce their own growth factors. What is this called? a. autonomous stimulation. b. autocrine stimulation. c. paracrine stimulation. d. endocrine stimulation.  EXAM(PLE) QUESTION What are the most important characteristics of an endocrine signal? a. The signal is noticed by other cells at a short distance and there is no need for cell-to-cell contact. b. The signal is noticed by other cells at a long distance and cell-to- cell contact is necessary. c. The signal is noticed by other cells at a short distance and cell-to- cell contact is necessary. d. The signal is noticed by other cells at long distance and there is no need for cell-to-cell contact.  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 🤔 extracellular signal molecule FIRST MESSENGERS CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules 1. ENZYME 2. SECOND MESSENGERS (3. ENZYME) effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein (4. SECOND MESSENGERS) altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 SELF STUDY - know and understand this terminology: SECOND MESSENGER (SMALL INTRACELLULAR MEDIATOR): Small intracellular signalling molecule that is formed or released for action in response to an extracellular signal and helps to relay the signal within the cell. Examples include cyclic AMP, cyclic GMP, IP3, Ca2+, and diacylglycerol (DAG). generated in large amounts in response to receptor activation diffuse away from their source, spreading the signal to other parts of the cell some (e.g. cyclic AMP, cyclic GMP, IP3 and Ca2+) are water soluble and diffuse in the cytosol others (e.g. diacylglycerol) are lipid soluble and diffuse in the plane of the plasma membrane pass on the signal by binding to and altering the behaviour of selected signalling or effector proteins  EXAM(PLE) QUESTION Many signal transduction pathways use second messengers to… a. transport a signal through the lipid bilayer of the plasma membrane b. relay a signal from the inside to the outside of the cell c. relay the message from the inside of the membrane throughout the cytoplasm d. amplify the message by phosphorylating proteins  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  extracellular signal molecule FIRST MESSENGERS CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules 1. ENZYME 2. SECOND MESSENGERS (3. ENZYME) effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein (4. SECOND MESSENGERS) altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1  extracellular signal molecule TH ES E EINS FIRST MESSENGERS P RO T E D T O BE NE C H E D ONCYTOSOL SWI T plasma membrane of target cell N D O FF)! (A SIGNAL TRANSDUCTION PATHWAY intracellular signalling molecules 1. ENZYME 2. SECOND MESSENGERS (3. ENZYME) effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein (4. SECOND MESSENGERS) altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1  MOLECULAR SWITCHES SIGNALLING BY PHOSPHORYLATION SIGNALLING BY GTP BINDING  MOLECULAR SWITCHES SIGNALLING BY PHOSPHORYLATION SIGNALLING BY GTP BINDING 🤓 SIGNALLING BY PHOSPHORYLATION intracellular signalling protein SIGNAL OFF IN P ATP protein protein kinase phosphatase ADP ON OFF P SIGNAL OUT see also figure 15-7 🤓 SIGNALLING BY PHOSPHORYLATION intracellular signalling protein SIGNAL OFF IN P ADP protein protein phosphatase kinase ATP P ON s i g n all ing So m e e r ot e i ns ar p y te d b SIGNAL act i va h o r y lat io n OUT sp de p ho an by e r t h rat h ! o r y l at i o n h p ho sp SELF STUDY - know and understand this terminology: PHOSPHORYLATION: reaction in which a phosphate group is covalently coupled to another molecule. PROTEIN KINASE: enzyme that transfers the terminal phosphate group of ATP to one or more specific amino acids (serine, threonine, or tyrosine) of a target protein. SERINE/THREONINE KINASE: enzyme that uses ATP to phosphorylate specific proteins on serine or threonine residues. TYROSINE KINASE: enzyme that phosphorylates specific proteins on tyrosine residues (found primarily in multicellular animals; not present in e.g. yeast). KINASE CASCADE: intracellular signalling pathway in which one protein kinase, activated by phosphorylation, phosphorylates the next protein kinase in the sequence, and so on, relaying the signal onward. PROTEIN PHOSPHATASE: enzyme that catalyzes phosphate removal from amino acids of a target protein.  EXAM(PLE) QUESTION Consider the following pathway: The components labelled with ‘X’ are also known as … X X a. protein kinases b. second messengers c. intracellular receptors d. carrier proteins  MOLECULAR SWITCHES SIGNALLING BY PHOSPHORYLATION SIGNALLING BY GTP BINDING  MOLECULAR SWITCHES SIGNALLING BY PHOSPHORYLATION SIGNALLING BY GTP BINDING 🤓 SIGNALLING BY GTP BINDING GTP binding protein OFF SIGNAL IN GDP P GDP GTP GTP binding hydrolysis GTP ON GTP SIGNAL OUT see also figure 15-7 🤓 SIGNALLING BY GTP BINDING INACTIVE MONOMERIC GTPase OFF SIGNAL IN GDP P GDP GTP GTP binding hydrolysis GTP ON GTP SIGNAL OUT see also figure 15-7 🤓 SIGNALLING BY GTP BINDING INACTIVE MONOMERIC GTPase OFF SIGNAL IN GDP P GDP GTP GTP binding hydrolysis GTP ON GTP ACTIVE MONOMERIC GTPase SIGNAL OUT see also figure 15-7 🤓 SIGNALLING BY GTP BINDING INACTIVE MONOMERIC GTPase OFF SIGNAL IN GDP P GDP GTP GEF hydrolysis GTP ON GTP ACTIVE MONOMERIC GTPase SIGNAL OUT Guanine nucleotide exchange factors (GEFs) activate the inactive protein by stimulating it to release its GDP; because the concentration of GTP in the cytosol is 10 times greater than the concentration of GDP, the protein rapidly binds GTP and is thereby activated. see also figure 15-8 🤓 SIGNALLING BY GTP BINDING INACTIVE MONOMERIC GTPase OFF SIGNAL IN GDP P GDP GEF GAP GTP ON GTP ACTIVE MONOMERIC GTPase SIGNAL OUT GTPase-activating proteins (GAPs) inactivate the protein by stimulating it to hydrolyse its bound GTP to GDP, which remains tightly bound to the inactivated GTPase. see also figure 15-8 SELF STUDY - know and understand this terminology: GTP-BINDING PROTEIN: an enzyme that converts GTP to GDP, usually has intrinsic GTPase activity. MONOMERIC GTP-BINDING PROTEIN: a single-subunit enzyme that converts GTP to GDP (also called monomeric GTPase). Cycles between an active GTP-bound form and frequently acts as a molecular switch in intracellular signalling pathways. GTPase-ACTIVATING PROTEIN (GAP): protein that binds to a GTPase and inhibits it by stimulating its GTPase activity, causing the enzyme to hydrolyze its bound GTP to GDP. GUANINE NUCLEOTIDE EXCHANGE FACTOR (GEF): protein that binds to a GTPase and activates it by stimulating it to release its tightly bound GDP, thereby allowing it to bind GTP in its place.  EXAM(PLE) QUESTION GTPase Activating Proteins (GAPs) a. Help turn small GTPases ON by promoting GDP/GTP exchange. b. Help turn small GTPases ON by inhibiting GTP hydrolysis. c. Help keep small GTPases OFF by inhibiting GDP/GTP exchange. d. Help turn small GTPases OFF by promoting GTP hydrolysis.  EXAM(PLE) QUESTION What is a TRUE statement about GTPases? a. GTPases are in an active conformation when they are bound to GDP. b. When GTPases are bound to GTP, GEF proteins can hydrolyse GTP to GDP, which changes the conformation of the GTPase. c. When GTPases are bound to GDP, GEF proteins can add a phosphate group to the GDP, thereby creating a GTP molecule. d. When GTPases are bound to GDP, GEF proteins can cause them to drop the GDP, opening up their nucleotide binding site for a new GTP to bind.  MOLECULAR SWITCHES SIGNALLING BY PHOSPHORYLATION SIGNALLING BY GTP BINDING  PRACTICE MAKES PERFECT!? INACTIVE INACTIVE GDP P P ATP A B GDP C D ADP GTP ACTIVE ACTIVE P GTP  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  extracellular signal molecule receptor protein CYTOSOL plasma membrane of target cell SIGNAL TRANSDUCTION PATHWAY intracellular signalling proteins effector proteins metabolic transcription cytoskeletal enzyme regulatory protein protein altered altered cell altered cellular response gene shape or metabolism expression movement see also figure 15-1 🤓 INTRACELLULAR SIGNALLING COMPLEXES FORM AT ACTIVATED CELL-SURFACE RECEPTORS PREFORMED SIGNALLING COMPLEX ON A SCAFFOLD PROTEIN ASSEMBLY OF SIGNALLING COMPLEX ON AN ACTIVATED RECEPTOR ASSEMBLY OF SIGNALLING COMPLEX ON PHOSPHOINOSITIDE DOCKING SITES 🤓 PREFORMED SIGNALLING COMPLEX ON A SCAFFOLD PROTEIN inactive receptor signal molecule CYTOSOL plasma membrane activated receptor 1 1 inactive activated scaffold 2 intracellular 2 intracellular protein signalling proteins signalling proteins 3 3 downstream signals see also figure 15-10 🤓 ASSEMBLY OF SIGNALLING COMPLEX ON AN ACTIVATED RECEPTOR inactive receptor signal molecule 1 P activated intracellular 2 P signalling 1 proteins 3 P inactive intracellular signalling 2 proteins activated receptor 3 downstream signals see also figure 15-10 🤓 ASSEMBLY OF SIGNALLING COMPLEX ON PHOSPHOINOSITIDE DOCKING SITES specific phospholipid signal molecule molecules (phosphoinositides) hyperphosphorylated phosphoinositides P P P P P P P P P P 2 1 2 1 activated intracellular downstream inactive intracellular signalling proteins signals signalling proteins see also figure 15-10 🤓 INTERACTION DOMAIN CYTOSOL plasma membrane 1 2 scaffold 2 protein 3 3 1 🤔 INTERACTION DOMAIN Examples: Src homology 2 (SH2) domains and phosphotyrosine-binding (PTB) domains 1 bind to phosphorylated tyrosines in a particular peptide sequence on activated receptors or intracellular signalling proteins. Src homology 3 (SH3) domains 2 bind to short, proline-rich amino acid sequences. Pleckstrin homology (PH) domains 3 bind charged head groups of specific phosphoinositides in the plasma membrane; enable their protein to dock on the membrane and interact with other signalling proteins. 🤓 ADAPTOR PROTEIN signal molecule plasma membrane CYTOSOL P P downstream relays signal protein downstream adaptor protein adaptor protein 🤓 ADAPTOR PROTEIN signal molecule plasma and What is the difference between a scaffold protein membrane an adaptor protein? CYTOSOL P P downstream relays signal protein downstream adaptor protein adaptor protein 🤔 FORMATION OF LARGE RECEPTOR CLUSTERS BY MULTIVALENT INTERACTIONS AMONG SIGNALLING PROTEINS could enhance cross-linking of extracellular the matrix to the membrane signal molecule proline-rich region plasma membrane activated CYTOSOL receptor P P P P P P P P P P P P P P P SH2 SH3 adaptor proteins see also figure 15-12 SELF STUDY - know and understand this terminology: SIGNALLING COMPLEX: Protein cluster that facilitates the processing of signals acting through signalling cascades. SCAFFOLD PROTEIN: Protein that binds groups of intracellular proteins into a complex, often anchoring the complex at a specific location in the cell (larger). INTERACTION DOMAIN: Compact protein module, found in many intracellular signalling proteins, that binds to a particular structural motif (for example, a short peptide sequence, a covalent modification, or another protein domain) in another protein or lipid. ADAPTOR PROTEIN: Protein that links typically two other proteins together in an intracellular signalling pathway or protein complex (smaller).  SELF STUDY - know and understand this terminology: Src homology 2 (SH2) domains and phosphotyrosine-binding (PTB) domains 1 bind to phosphorylated tyrosines in a particular peptide sequence on activated receptors or intracellular signalling proteins. Src homology 3 (SH3) domains bind to short, proline-rich amino acid 2 sequences. Pleckstrin homology (PH) domains bind charged head groups of specific 3 phosphoinositides in the plasma membrane; enable their protein to dock on the membrane and interact with other signalling proteins.  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview 🤓 TWO CLASSES OF RECEPTORS CELL SURFACE RECEPTORS INTRACELLULAR RECEPTORS plasma membrane small, hydrophobic signal molecule cell-surface receptor protein target cell carrier protein hydrophilic signal nucleus molecule target cell intracellular receptor protein see also figure 15-3  TWO CLASSES OF RECEPTORS CELL SURFACE RECEPTORS INTRACELLULAR RECEPTORS plasma membrane small, hydrophobic signal molecule cell-surface receptor protein target cell carrier protein hydrophilic signal nucleus molecule target cell intracellular receptor protein i) ION-CHANNEL-COUPLED RECEPTORS ii) G-PROTEIN—COUPLED RECEPTORS / GPCRs iii) ENZYME-COUPLED RECEPTORS see also figure 15-3  i) ION-CHANNEL-COUPLED RECEPTORS ions receptor signal molecule protein plasma membrane see also figure 15-6  i) ION-CHANNEL-COUPLED RECEPTORS ions receptor signal molecule protein plasma membrane s e d as s Dis cu f par t o p t e r 11. C ha see also figure 15-6  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview  ii) GPCRs largest and most versatile family of LIGAND N cell-surface receptors EXTRACELLULAR SPACE largest protein family encoded by the human genome mediate most responses to external and internal signals C CYTOSOL numerous ligands plasma membrane (one of) the most successful GPCR therapeutic target families! see also figure 15-22 (S)-alpha-methyl-4-carboxyphenylglycine, Abaloparatide, Acamprosate, Acebutolol, Acetophenazine, Acetylcholine, Acetylholine, Aclidinium, Acrivastine, Adomeglivant, Agomelatine, Albiglutide, Alcaftadine, Alfuzosin, Alimemazine, Alipiprazole, Almotriptan, Alosetron, Alverine, Amantadine, Amiodarone, Amisulpride, Amitriptyline, Amitrriptyline, Amoxapine, Amphetamine, Amytriptyline, Angiotensin II, Anisotropine methylbromide, Antazoline, Apomorphine, Apraclonidine, Arbutamine, Arformoterol, Aripiprazole, Aripiprazole lauroxil, Asenapine, Astemizole, Atenolol, Atropine, Azatadine, Azelastine, Azilsartan medoxomil, Baclofen, Benzatropine, Benzphetamine, Bepotastine, Betahistine, Betaxolol, Betazole, Bethanechol, Bethanidine, Bevacizumab, Bilastine, Biperiden, Bisoprolol, Brexpiprazole, Brimonidine, Bromocriptine, Bromodiphenhydramine, Brompheniramine, Buclizine, Bupropion, Buspirone, Butriptyline, Butylscopolamine, Cabergoline, Cabozantinib, Calcium citrate, Candesartan, Cannabidiol, Carbamoylcholine, Carbinoxamine, Cariprazine, Carteolol, Carvedilol, Celiprolol, Cetirizine, Cevimeline, Chlorcyclizine, Chlordiazepoxide, Chloroprocaine, Chlorpheniramine, Chlorpromazine, Chlorprothixene, Cimetidine, Cinacalcet, Cinnarizine, Cisapride, Cisplatin, Citalopram, Clemastine, Clenbuterol, Clidinium, Clofedanol, Clomipramine, Clonidine, Clozapine, Cocaine, Colestipol Hydrochloride, Conivaptan, Corticorelin ovine triflutate, Cryptenamine, Cyclizine, Cyclobenzaprine, Cyclopentolate, Cycrimine, Cyproheptadine, Dapiprazole, Darifenacin, Desipramine, Desloratadine, Dexbrompheniramine, Dexchlorpheniramine maleate, Dexfenfluramine, Dexmedetomidine, Dextroamphetamine, Dicyclomine, Dihydro- alpha-ergocryptine, Dihydroergocornine, Dihydroergocristine, Dihydroergotamine, Dimenhydrinate, Dimetindene, Diphemanil, Diphenhydramine, Diphenidol, Diphenylpyraline, Dipivefrin, Disopyramide, Disulfiram, DL-Methylephedrine, Dobutamine, Dolasetron, Domperidone, Donepezil, Dopamine, Dosulepin, Doxacurium, Doxazosin, Doxepin, Doxidopa, Doxylamine, Dronedarone, Droperidol, Droxidopa, Dulaglutide, Edrophonium, Eletriptan, Emedastine, Ephedrine, Epicriptine, Epinastine, Epinephrine, Eprosartan, Eptinezumab, Erenumab, Ergoloid, Ergoloid mesylate, Ergometrine, Ergotamine, Escitalopram, Esmolol, Etafedrine, Etelcalcetide, Ethanol, Etomidate, Exenatide, Ezetimibe, Famotidine, Fenfluramine, Fenoldopam, Fenoterol, Fesoterodine, Fexofenadine, Fimasartan, Flavoxate, Flibanserin, Flucinonide, Flunarizine, Fluoxetine, Flupentixol, Fluphenazine, Fluspirilene, Forasartan, Formoterol, Frovatriptan, Gallamine triethiodide, Gamma-Aminobutyric acid, Gilteritinib, Glasdegib, Glucagon, Glutamic acid, Glycopyrronium, Granisetron, Guanabenz, Guanfacine, Halcinonide, Haloperidol, Hexocyclium, Histamine, Homatropine, Hydroxyzine, Hyoscyamine, Iloperidone, Imipramine, Indacaterol, Indigotindisulfonic acid, Indoramin, Ipatropium, Irbesartan, Isoetharine, Isometheptene, Isoprenaline, Isopropamide, Ketamine, Ketanserin, Ketotifen, Labetalol, Lamotrigine, Lasmiditan, Lenalidomide, Levobetaxolol, Levobunolol, 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Ziprasidone, Zolmitriptan, Zotepine, Zuclopenthixol; doi.org/10.1038/s41392-020-00435-w  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview 🤓 ii) GPCRs signal molecule inactive inactive inactive activated receptor receptor G protein enzyme and G protein activated enzyme activated G protein see also figure 15-6 🤓 G PROTEINS ARE HETEROTRIMERIC GTP-BINDING PROTEINS G proteins: composed of three subunits (α, β, and γ) α β γ GDP covalently attached lipid molecules (anchorage to plasma membrane) inactive G protein unstimulated: GDP is bound see also figure 15-23 🤓 UPON ACTIVATION GPCR ACTS AS A GEF - α SUBUNIT RELEASES BOUND GDP ALLOWING GTP BINDING signal molecule α β γ α β γ GDP inactive inactive GDP receptor G protein α β γ GTP downstream signalling activated G protein see also figure 15-23 🤓 HETEROTRIMERIC GTP-BINDING PROTEINS HAVE INTRINSIC GTPase ACTIVITY signal molecule α β γ α β γ GDP inactive inactive GDP receptor G protein α is a GTPase can hydrolyse its α β γ bound GTP to GDP GTP (inactivation) downstream signalling activated G protein see also figure 15-23 🤓 GTP HYDROLYSIS CAN BE ENHANCED BY A REGULATOR OF G PROTEIN SIGNALLING signal molecule α β γ α β γ GDP inactive inactive GDP receptor G protein α β γ RGS GTP downstream signalling α-subunit-specific GAP activated G protein aids in terminating G-protein-mediated responses see also figure 15-23 🤯 FOUR MAJOR FAMILIES OF HETEROTRIMERIC G PROTEINS SUBUNITS EXAMPLES OF MEDIATING FAMILY EXAMPLES OF FUNCTIONS FAMILY MEMBERS ACTION I Gs α Activates adenylyl cyclase; activates Ca2+ channels Golf α Activates adenylyl cyclase in olfactory sensory neurons II Gi α Inhibits adenylyl cyclase βγ Activates K+ channels Go βγ Activates K+ channels; inactivates Ca2+ channels α and βγ Activates phospholipase C-β Gt (transducin) α Activates cyclic GMP phosphodiesterase in vertebrate rod photoreceptors III Gq α Activates phospholipase C-β IV G12/13 α Activates Rho family monomeric GTPases (via Rho GEF) to regulate the actin cytoskeleton 🤓 FOUR MAJOR FAMILIES OF HETEROTRIMERIC G PROTEINS SUBUNITS EXAMPLES OF MEDIATING FAMILY EXAMPLES OF FUNCTIONS FAMILY MEMBERS ACTION I Gs α Activates adenylyl cyclase; activates Ca2+ channels Golf α Activates adenylyl cyclase in olfactory sensory neurons II Gi α Inhibits adenylyl cyclase βγ Activates K+ channels Go βγ Activates K+ channels; inactivates Ca2+ channels α and βγ Activates phospholipase C-β Gt (transducin) α Activates cyclic GMP phosphodiesterase in vertebrate rod photoreceptors III Gq α Activates phospholipase C-β IV G12/13 α Activates Rho family monomeric GTPases (via Rho GEF) to regulate the actin cytoskeleton SELF STUDY - know and understand this terminology: G-PROTEIN COUPLED RECEPTOR (GPCR): A seven-pass cell-surface receptor that, when activated by its extracellular ligand, activates a G protein, which in turn activates either an enzyme or ion channel in the plasma membrane. G PROTEIN (HETEROTRIMERIC GTP-BINDING PROTEIN): A heterotrimeric GTP-binding protein with intrinsic GTPase activity that couples GPCRs to enzymes or ion channels in the plasma membrane. REGULATOR OF G PROTEIN SIGNALLING (RGS): A type of GAP protein that binds to a trimeric G protein and enhances its GTPase activity, thus helping to limit G-protein-mediated signalling.  TODAY’S MENU what is cell signalling? concepts in cell signalling response time positive and negative feedback signal integration cell-dependent responses cell surface and intracellular receptors types of cell signalling second messengers molecular switches signalling complexes types of cell surface receptors G-protein-coupled receptors G-proteins enzyme activation signal amplification desensitisation nitric oxide signalling enzyme-coupled receptors enzyme activation signalling pathway overview ii) GPCRs: the next step SIGNALLING BY SIGNALLING BY ADENYLYL CYCLASE PHOSPHOLIPASE C AND cAMP AND Ca2+ ii) GPCRs: the next step SIGNALLING BY SIGNALLING BY ADENYLYL CYCLASE PHOSPHOLIPASE C AND cAMP AND Ca2+  signal molecule inactive inactive activated receptor receptor G protein and G protein activated G protein see also figure 15-6  signal molecule inactive inactive inactive activated receptor receptor G protein enzyme and G protein activated enzyme activated G protein see also figure 15-6  signal molecule inactive inactive inactive activated receptor receptor G protein enzyme and G protein activated enzyme activated G protein see also figure 15-6 🤓 ADENYLYL CYCLASE IS A MEMBRANE-BOUND ENZYME THAT CATALYSES FORMATION OF CYCLIC AMP (cAMP) FROM ATP signal molecule inactive inactive inactive activated receptor receptor G protein adenylyl and G protein cyclase activated adenylyl cyclase activated G protein see also figure 15-6 🤓 cAMP = CYCLIC ADENOSINE MONOPHOSPHATE P + P NH2 NH2 N N pyrophosphate P P N N O O O N N N N CH2 O O P O P O P O CH2 O O O O adenylyl ATP cyclase O cAMP O P O OH OH OH O NH2 H2O N N cyclic AMP O N N phosphodiesterase O P O CH2 O O 5’-AMP OH OH see also figure 15-26 🤓 cAMP EXERTS EFFECTS THROUGH ACTIVATION OF CYCLIC-AMP-DEPENDENT PROTEIN KINASE (PROTEIN KINASE A; PKA) cyclic AMP inactive PKA and (tetramer) regulatory inactive active catalytic subunit catalytic subunits subunit activity of intracellular signalling and effector kinase activity proteins see also figure 15-27 🤓 PKA-MEDIATED RESPONSES CAN BE SLOW OR RAPID activated adenylyl cyclase signal molecule activated α subunit of CYTOSOL stimulatory G plasma protein (Gs) membrane NUCLEUS CYTOSOL nuclear pore activated PKA GTP activated GPCR activated, phosphorylated CREB ATP inactive CREB CREB-binding P protein (CBP) cyclic AMP activated target gene cyclic AMP response element (CRE) GENE TRANSCRIPTION inactive PKA activated PKA PROTEIN ACTIVITY see also figure 15-28 SELF STUDY - know and understand this terminology: ADENYLYL CYCLASE: Membrane-bound enzyme that catalyses the formation of cyclic AMP from ATP. CYCLIC AMP (cAMP): Nucleotide that is generated from ATP by adenylyl cyclase in response to various extracellular signals. It acts as a small intracellular signalling molecule, mainly by activating cAMP-dependent protein kinase (PKA). It is hydrolyzed to AMP by a phosphodiesterase. CYCLIC AMP PHOSPHODIESTERASE: Specific enzyme that rapidly and continually destroys cyclic AMP, forming 5’-AMP. PROTEIN KINASE A (PKA): Enzyme that phosphorylates target proteins in response to a rise in intracellular cyclic AMP. Amongst others, one of its targets is the nuclear factor CREB. CRE-BINDING (CREB) PROTEIN: Transcription regulator that recognises the cyclic AMP response element (CRE) in the regulatory region of genes activated by cAMP. On activation by PKA, phosphorylated CREB recruits a transcriptional coactivator (CREB-binding protein; CBP) to stimulate transcription of target genes.  EXAM(PLE) QUESTION Caffeine is a phosphodiesterase inhibitor. Based on what you know of cAMP flux in the cell, which of the following might you see as a result of excessive caffeine intake by a pharmacy student cramming for the MBOCII exam? a. cAMP levels will increase. b. AMP levels will increase. c. Adenylyl cyclase activity will increase. d. Protein kinase A activity will decrease.  EXAM(PLE) QUESTION The activity of protein kinase A (PKA) is regulated by cAMP. Which statement correctly describes the role of cAMP in this activation? a. cAMP binds to the active site of PKA, promoting its association with its substrates. b. PKA needs cAMP to act as a source of energy for the catalytic reaction. c. cAMP binds to the catalytic subunit of PKA, promoting association of the pseudosubstrate and activating it. d. cAMP binds to the regulatory subunit of PKA, promoting its dissociation from the catalytic subunit and activating it. 🤓 A STIMULATORY GPCR ACTS VIA A STIMULATORY G PROTEIN (Gs), WHOSE ACTIVATED α SUBUNIT ACTIVATES ADENYLYL CYCLASE. signal molecule inactive inactive inactive activated receptor receptor G protein enzyme and G protein STIMULATORY G PROTEIN (Gs) ATP activated enzyme activated G protein cAMP see also figure 15-6 🤓 AN INHIBITORY GPCR ACTS VIA AN INHIBITORY G PROTEIN (Gi), WHOSE ACTIVATED α SUBUNIT INHIBITS ADENYLYL CYCLASE. signal molecule inactive inactive inactive activated receptor receptor G protein enzyme and G protein INHIBITORY G PROTEIN (Gi) ATP activated enzyme activated G protein cAMP see also figure 15-6 SELF STUDY - know and understand this terminology: STIMULATORY G PROTEIN (Gs): Heterotrimeric G protein that, when activated, activates the enzyme adenylyl cyclase and thus stimulates the production of cyclic AMP. INHIBITORY G PROTEIN (Gi): Heterotrimeric G protein that, when activated, inhibits the enzyme adenylyl cyclase and thus inhibits the production of cyclic AMP. 🫣 A STIMULATORY GPCR ACTS VIA A STIMULATORY G PROTEIN (Gs), WHOSE ACTIVATED α SUBUNIT ACTIVATES ADENYLYL CYCLASE. signal molecule inactive inactive inactive activated receptor receptor G protein enzyme and G protein in ra tox C ho le e s Gs : u l a t tim o vers t i ve e d ’ in ac lo ck Gsα ‘ s t i m u la te s - s tate ATP c y c la se activated y l y l ad e n i n i te l y enzyme i n d ef activated G protein cAMP see also figure 15-6 🫣 AN INHIBITORY GPCR ACTS VIA AN INHIBITORY G PROTEIN (Gi), WHOSE ACTIVATED α SUBUNIT INHIBITS ADENYLYL CYCLASE. signal molecule inactive inactive inactive activated receptor receptor G protein enzyme and G protein ts x i n inh ibi o ssis t f Pe r t u i b i t io n o h Gi (in tio n inh ibi ): t i m u lat io n = s ve ’ i n inact i d lo cke s tate - Giα ‘ e r i c ) ATP ot r i m ed activated ( h eter i ng b lo ck l l sig na enzyme activated G protein cAMP see also figure 15-6  EXAM(PLE) QUESTION A GPCR signals through a stimulatory G-protein, which in turn signals through adenylyl cyclase. What will happen to adenylyl cyclase upon activation of the receptor? a. Adenylyl cyclase will be activated. b. Adenylyl cyclase will be inhibited. c. Activity of adenylyl cyclase will remain the same. d. Adenylyl cyclase will be proteolytically degraded. 🫣 THE MORPHINE RECEPTOR IS A GPCR morphine inactive inactive inactive activated receptor receptor G protein adenylyl and G protein cyclase inactive adenylyl cyclase activated G protein 🫣 THE MORPHINE RECEPTOR IS A GPCR morphine inactive inactive inactive activated receptor receptor G protein adenylyl and G protein cyclase Ca2+ K+ open K+ channel inactive closed Ca2+ channel adenylyl cyclase RELEASE OF NEUROTRANSMITTERS activated G protein GENE TRANSCRIPTION 🫣 THE MORPHINE RECEPTOR IS A GPCR displaces morphine from the GPCR naloxone (antagonistic) morphine (agonist) inactive inactive inactive activated receptor receptor G protein adenylyl and G protein cyclase Ca2+ K+ open K+ channel Giα inactive closed Ca2+ channel adenylyl cyclase RELEASE OF NEUROTRANSMITTERS activated G protein GENE TRANSCRIPTION 🫣 THE MORPHINE RECEPTOR IS A GPCR displaces morphine from the GPCR naloxone (antagonistic) morphine (agonist) inactive inactive inactive activated receptor receptor G protein adenylyl and G protein cyclase Ca2+ K+ open K+ channel o r p h in e M es Giα re d u c inactive closed Ca channel t i c sy nap 2+ adenylyl i g n all i ng cyclase s RELEASE OF NEUROTRANSMITTERS activated G protein GENE TRANSCRIPTION ii) GPCRs: the next step SIGNALLING BY SIGNALLING BY ADENYLYL CYCLASE PHOSPHOLIPASE C AND cAMP AND Ca2+ ii) GPCRs: the next step SIGNALLING BY SIGNALLING BY ADENYLYL CYCLASE PHOSPHOLIPASE C AND cAMP AND Ca2+ 🤓 G PROTEINS CAN ALSO SIGNAL VIA PHOSPHOLIPIDS signal molecule activated GPCR activated phospholipase C-β α β γ GTP activated Gq protein see also figure 15-30 🤓 G PROTEINS CAN ALSO SIGNAL VIA PHOSPHOLIPIDS phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2, PIP2] signal molecule activated GPCR activated diacylglycerol phospholipase C-β (DAG) P α β P γ GTP P P P activated Gq protein P inositol 1,4,5- triphosphate (IP3) see also figure 15-30 🤓 phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2, PIP2] phosphatidylserine activated diacylglycerol phospholipase C-β (DAG) P targets P activated protein kinase C cleavage P P calmodulin P Ca2+ CaM inositol P 1,4,5-triphosphate CaM-kinase (IP3) open IP3-gated II Ca2+-release channel lumen of endoplasmic reticulum targets see also figure 15-30 SELF STUDY - know and understand this terminology: Gq-TYPE G PROTEIN (Gq): Heterotrimeric G protein that, when activated, activates the enzyme phospholipase C, and thus catalyses generation of inositol triphosphate (IP3) and diacylglycerol (DAG) from PIP2. PHOSPHOLIPASE C (PLC): Membrane-bound enzyme that cleaves inositol phospholipids to produce IP3 and diacylglycerol. PLCβ is activated by GPCRs via specific G proteins. INOSITOL 1,4,5-TRIPHOSPHATE (IP3): Small intracellular signalling molecule produced during activation of the inositol phospholipid signalling pathway. Acts to release Ca2+ from the endoplasmic reticulum. IP3 RECEPTOR (IP3-GATED Ca2+-RELEASE CHANNEL): Gated Ca2+ channel in the endoplasmic reticulum membrane that opens on binding cytosolic IP3, releasing stored Ca2+ in the cytosol. DIACYLGLYCEROL (DAG): Lipid produced by the cleavage of inositol phospholipids in response to extracellular signals. Composed of two fatty acid chains linked to glycerol, it serves as a small signalling molecule to help activate prtoein kinase C (PKC). SELF STUDY - know and understand this terminology: PROTEIN KINASE C (PKC): Ca2+-dependent protein kinase that, when activated by diacylglycerol and an increase in the concentration of cytosolic Ca2+, phosphorylates target proteins on specific serine and threonine residues. CALMODULIN: Ubiquitous intracellular Ca2+-binding protein that undergoes a large conformation change when it binds Ca2+, allowing it to regulate the activity of many target proteins. In its activated (Ca2+-bound) form, it is called Ca2+/calmodulin. Ca2+/CALMODULIN-DEPENDENT KINASE (CaM-KINASE II): Serine/threonine protein kinase that is activated by Ca2+/calmodulin. Indirectly mediates the effects of an increase in cytosolic Ca2+ by phosphorylating specific target proteins.  EXAM(PLE) QUESTION Mastoparan is a peptide toxin from wasp venom. It acts as an activator of the heterotrimeric Gq protein. What do you expect will happen in the cell? a. A rise in cAMP. b. A rise in IP3. c. A decline in Ca2+. d. An increase in adenylyl cyclase activity.  EXAM(PLE) QUESTION You are measuring Ca2+ levels in the cytosol of a cell using a Ca2+- sensitive dye. After adding an extracellular signal molecule, you see a rise in signal and therefore cytosolic Ca2+. Which of the following factors is most likely to have been activated by the extracellular signal? a. CaM-kinase II. b. adenylyl cyclase. c. phospholipase C-β. d. protein kinase C.  TODAY’S MENU what is cell signalling? concepts in cell signalling re