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Cell Signaling AP Chapter 11
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Evolution of cell signaling
Similarities in pathways in bacteria, protists, fungi, plants, and animals suggest an early evolution of signaling pathways
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Bacteria communication “bacteria talking to each other”
Quorum sensing- concentration of signaling molecules allows bacteria to sense their local density Ex- Vibrio – glowing bacteria (luciferase enzyme) give off auto inducers into their environment
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autoinducers
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Quorum sensing can lead to the formation of biofilms
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Slime molds – chemical signaling
Slime molds live as solitary amoebae. When slime mold cells begin to starve or dehydrate, they release a pheromone-like chemical called cyclic AMP. This messenger molecule alerts other slime mold amoebae. They detect the cAMP and follow the scent to join forces with the troubled amoebae forming a large mass of cells. Other slime mold amoebae detect the cAMP and follow the scent to join forces with the troubled amoebae.
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cAMP is an important chemical word in the language of cells and seems to be understood and made by all cells, even our own.
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Fruiting body formation in fungi chemical signaling
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Local and long-distance signaling
Direct cytoplasmic connections: - gap junctions or plasmodesmata in plant cells - contact of surface molecules (cell-to- cell recognition via receptors
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Plasmodesmata in plant cells
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Gap junctions in animal cells
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Immune cells – direct contact
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Local regulators – nearby cells
paracrine signaling – only includes cells of a particular organ synaptic signaling – between neurons
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Long distance endocrine signaling nerve transmission
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3 stages of cell signaling
Reception Transduction Response
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Plasma membrane 1 Reception Receptor Signaling molecule 1
Fig EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception Receptor Figure 11.6 Overview of cell signaling Signaling molecule
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Plasma membrane 1 Reception Transduction Receptor Signaling molecule 1
Fig EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception 2 Transduction Receptor Relay molecules in a signal transduction pathway Figure 11.6 Overview of cell signaling Signaling molecule
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Plasma membrane 1 Reception Transduction Response Receptor Activation
Fig EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 Reception 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Figure 11.6 Overview of cell signaling Signaling molecule
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Reception Ligand – the signal molecule, fits like a lock and key to receptor Most ligands bind to cell surface receptors; some bind to intracellular receptors Usually induces a shape change in receptor protein’s shape
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Types of receptors Bind with water-soluble molecules on membrane:
G-Protein-linked Receptor Tyrosine Kinase Receptor Ligand-gated Ion Channel Bind with hydrophobic receptors: Intracellular Receptors
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G- Protein-Linked Receptors
7 protein helices that span the membrane Binding of the ligand to the G-protein receptor, activates a specific G protein located on the cytoplasm side. How - GDP becomes GTP. The activated G-protein activates a membrane-bound enzyme which continues on its pathway. The GTP goes back to GDP. Animation: Membrane-Bound Receptors that Activate G Proteins
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Signaling-molecule binding site
Fig. 11-7a Signaling-molecule binding site Figure 11.7 Membrane receptors—G protein-coupled receptors, part 1 Segment that interacts with G proteins G protein-coupled receptor
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Figure 11.7 Membrane receptors—G protein-coupled receptors, part 2
Fig. 11-7b Plasma membrane G protein-coupled receptor Inactive enzyme Activated receptor Signaling molecule GDP G protein (inactive) Enzyme GDP GTP CYTOPLASM 1 2 Activated enzyme Figure 11.7 Membrane receptors—G protein-coupled receptors, part 2 GTP GDP P i Cellular response 3 4
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How important is the G-protein system?
Used by hormones, neurotransmitters, sensory reception, development…. Many bacteria produce toxins that interfere with with G-protein systems Up to 60% of medicines influence G-protein pathways
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Tyrosine kinase receptors
Receptor tyrosine kinases are membrane receptors that attach phosphates from ATP to tyrosines (Remember kinase…ATP.) Once the receptors are activated, relay proteins bind to them and become activated themselves. A receptor tyrosine kinase can trigger multiple signal transduction pathways at once
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Fully activated receptor tyrosine kinase
Fig. 11-7c Signaling molecule (ligand) Ligand-binding site Signaling molecule Helix Tyr Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins Dimer CYTOPLASM 1 2 Activated relay proteins Figure 11.7 Membrane receptors—receptor tyrosine kinases Cellular response 1 Tyr Tyr P Tyr Tyr P Tyr Tyr P P Tyr Tyr P Tyr Tyr P Tyr Tyr P P Cellular response 2 Tyr Tyr P Tyr Tyr P Tyr P Tyr P 6 ATP 6 ADP Activated tyrosine kinase regions Fully activated receptor tyrosine kinase Inactive relay proteins 3 4
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Tyrosine Kinase Receptors
Binding of the signal molecules causes the two polypeptides to join.
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They are activated and act as enzymes to phosphorylate the tyrosines in the tails.
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The receptor protein is now recognized by relay proteins, triggering different effects.
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Ligand-gated ion channel
A ligand-gated ion channel receptor acts as a gate When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor Ex- in neurotransmitters and nervous signal transmission
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1 Signaling molecule (ligand) Gate closed Ions Plasma membrane
Fig. 11-7d 1 Signaling molecule (ligand) Gate closed Ions Plasma membrane Ligand-gated ion channel receptor 2 Gate open Cellular response Figure 11.7 Membrane receptors—ion channel receptors 3 Gate closed
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Ligand-Gated Ion Channels
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Intracellular Receptors
Some receptor proteins are intracellular, found in the cytosol or nucleus of target cells Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors Examples of hydrophobic messengers are the steroid and thyroid hormones of animals An activated hormone-receptor complex can act as a transcription factor, turning on specific genes
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Hormone (testosterone) Plasma membrane Receptor protein Hormone-
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein Hormone- receptor complex DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor mRNA NUCLEUS New protein CYTOPLASM
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Intracellular Receptors
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Signal Transduction Allow for amplification of signals
Signal coordination and regulation Involves 1) second messengers (cAMP and Ca+2) 2) relay proteins such as protein kinases
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How does epinephrine work?...an example of cAMP messenging
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Epinephrine acts via cyclic AMP (cAMP) as a second messenger.
An activated G protein activates the enzyme adenylyl cyclase (THINK CYCLING!) which turns ATP to cAMP. Then cAMP can activate other inactive molecules to reach the desired product. action of epinephrine Video | DnaTube.com - Scientific Video Site
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Figure 11.10 Cyclic AMP Adenylyl cyclase Phosphodiesterase
Pyrophosphate P P i ATP cAMP AMP Figure Cyclic AMP
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First messenger Adenylyl cyclase G protein GTP G protein-coupled
Fig First messenger Adenylyl cyclase G protein G protein-coupled receptor GTP ATP Second messenger cAMP Figure cAMP as second messenger in a G-protein-signaling pathway Protein kinase A Cellular responses
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cAMP second messenger systems
Membrane Structure
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Calcium ions also act as second messengers.
One example is activating an enzyme phospholipase C to produce two more messengers which will open Ca channels. The signal receptor may be a G protein or a tyrosine kinase receptor.
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EXTRA- CELLULAR FLUID Signaling molecule (first messenger) G protein
Fig EXTRA- CELLULAR FLUID Signaling molecule (first messenger) G protein DAG GTP G protein-coupled receptor PIP2 Phospholipase C IP3 (second messenger) IP3-gated calcium channel Figure Calcium and IP3 in signaling pathways Endoplasmic reticulum (ER) Various proteins activated Cellular responses Ca2+ Ca2+ (second messenger) CYTOSOL
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RELAY PROTEINS Enzymes called protein kinases are also important links in transduction. A protein kinase catalyzes the transfer of PHOSPHATE GROUPS from ATP to another protein to activate it. Amplification is possible in these type of pathways.
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Phosphorylation cascade
Fig. 11-9 Signaling molecule Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP Phosphorylation cascade ADP Active protein kinase 2 P PP P i Inactive protein kinase 3 Figure 11.9 A phosphorylation cascade ATP ADP Active protein kinase 3 P PP P i Inactive protein ATP ADP P Active protein Cellular response PP P i
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This can get pretty complicated!
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Cell Responses Alteration of metabolism Rearrangement of cytoskeleton
Modulation of gene activity
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Modulating Gene Activity Growth factor Reception Receptor
Fig Growth factor Reception Receptor Modulating Gene Activity Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor Figure Nuclear responses to a signal: the activation of a specific gene by a growth factor Response P DNA Gene NUCLEUS mRNA
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Alteration of Metabolism Reception Transduction Inactive G protein
Fig Reception Binding of epinephrine to G protein-coupled receptor (1 molecule) Transduction Inactive G protein Active G protein (102 molecules) Alteration of Metabolism Inactive adenylyl cyclase Active adenylyl cyclase (102) ATP Cyclic AMP (104) Inactive protein kinase A Active protein kinase A (104) Figure Cytoplasmic response to a signal: the stimulation of glycogen breakdown by epinephrine Inactive phosphorylase kinase Active phosphorylase kinase (105) Inactive glycogen phosphorylase Active glycogen phosphorylase (106) Response Glycogen Glucose-1-phosphate (108 molecules)
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Rearrangement Of cytoskeleton RESULTS CONCLUSION
Fig RESULTS Rearrangement Of cytoskeleton Wild-type (shmoos) ∆Fus3 ∆formin CONCLUSION Mating factor 1 Shmoo projection forming G protein-coupled receptor Formin P Fus3 Actin subunit Figure How do signals induce directional cell growth in yeast? GTP P GDP 2 Phosphory- lation cascade Formin Formin P 4 Microfilament Fus3 Fus3 P 5 3
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Fine-Tuning of the Response
Multistep pathways have two important benefits: Amplifying the signal (and thus the response) Contributing to the specificity of the response Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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The Specificity of Cell Signaling and Coordination of the Response
Different kinds of cells have different collections of proteins which allow cells to detect and respond to different signals. Even the same signal can have different effects in cells with different proteins and pathways
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Fig Signaling molecule Same signal - different effects in cells with different proteins and pathways Receptor Relay molecules Response 1 Response 2 Response 3 Cell A. Pathway leads to a single response. Cell B. Pathway branches, leading to two responses. Pathway branching and “cross-talk” further help the cell coordinate incoming signals Figure The specificity of cell signaling Activation or inhibition Response 4 Response 5 Cell C. Cross-talk occurs between two pathways. Cell D. Different receptor leads to a different response.
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Signaling Efficiency: Scaffolding Proteins and Signaling Complexes
Scaffolding proteins are large relay proteins to which other relay proteins are attached Scaffolding proteins can increase the signal transduction efficiency by grouping together different proteins involved in the same pathway
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Signaling Plasma molecule membrane Receptor Three different protein
Fig Signaling molecule Plasma membrane Receptor Three different protein kinases Figure A scaffolding protein Scaffolding protein
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Apoptosis is programmed or controlled cell suicide
Apoptosis (programmed cell death) integrates multiple cell-signaling pathways Apoptosis is programmed or controlled cell suicide A cell is chopped and packaged into vesicles that are digested by scavenger cells Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells Apoptosis is important in shaping an organism during embryonic development
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Ced-9 (inactive) Cell forms blebs Death- signaling molecule Active
Fig b Ced-9 (inactive) Cell forms blebs Death- signaling molecule Active Ced-4 Active Ced-3 Other proteases Nucleases Figure Molecular basis of apoptosis in C. elegans Activation cascade (b) Death signal
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Apoptotic Pathways and the Signals That Trigger Them
Caspases are the main proteases (enzymes that cut up proteins) that carry out apoptosis Apoptosis can be triggered by: An extracellular death-signaling ligand DNA damage in the nucleus Protein misfolding in the endoplasmic reticulum Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Apoptosis evolved early in animal evolution and is essential for the development and maintenance of all animals Apoptosis may be involved in some diseases (for example, Parkinson’s and Alzheimer’s); interference with apoptosis may contribute to some cancers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Interdigital tissue 1 mm
Fig Interdigital tissue 1 mm Figure Effect of apoptosis during paw development in the mouse
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