Lecture 15: Cell communication-signalling through G-protein coupled receptors Flashcards by Allie Skinkle

Why is intercellular communication necessary?

Cellular differentiation and specialization
Growth stimulation or termination
Tissue formation
Integration of metabolism

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General Signaling Pathway?

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What are the three types of effector proteins?

metabolic enzyme
transcription regulatory protein
cytoskeletal protein

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4 types of signal distribution?

contact-dependent
paracrine/autocrine
synaptic
endocrine

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What is the fast effect of signaling?

altered protein function

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What is the slow effect of signaling?

altered protein synthesis

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Endocrine signals are ___ in concentration and its receptors are ____ affinity

low conc

high affinity

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Synaptic signals are ___ in concentration and its receptors are ____ affinity

high conc

low affinity

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Chemical types of signaling molecules

Amino acid derivatives
Nucleotides
Lipids

– Steroids

– Arachidonic acid metabolites

-eicosanoids

– Retinoids

Peptides
Gases

– Nitric Oxide (NO)

– Carbon Monoxide (CO)

• Protons

– C. elegans muscle

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Amino Acid derived signals are ____

shorter lifespan, more paracrine-like

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Steroid signals are relatively ____ lasting

long

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Steroid signals are derived from ____’s structure

cholesterol

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Eicosanoids are derived from ___’s structure

arachodonic acid

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Peptide hormones include:

Pituitary hormones
hypothalamic hormones
thyroid hormones
digestive hormones
pancreatic hormones

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Nitric Oxide is a ____

vasodilator

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Nitric oxide synthase transforms ____ into NO and citroline

arginine

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NO diffuses out of the ____ cell into the ____ cell

endothelial to smooth muscle

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What is the name of the cytosolic intracellular receptor NO binds to?

guanyl cyclase

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Membrane soluble signals (those that bind to intracellular receptors) require ____ to navigate the aqeous environment outside the cells

carrier proteins

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Cell-surface receptors usually bind to ____ signals.

hydrophilic

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Intracellular receptors

Nuclear receptor superfamily
Steroid hormone receptors are ligand-activated transcription factors
They are modular in construction

– Ligand binding domain

– DNA-binding domain

– Variable region

• Generally function with other binding partners

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What are the three domains of a steriod receptor? where are they located?

N-terminus: transcription-activating domain

Middle: DNA-binding domain

C-terminus: ligand-binding domain

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Response induced by steroid hormone receptor activation

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The presence of a hormone or ligand is sensed by an ____

integral membrane protein receptor

• This information is communicated across the cell membrane and transmitted by intracellular signaling molecules.

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Small intracellular mediators are also referred to as \_\_\_\_

“second messengers”

Second messengers illicit various cellular responses:

- Activate or inhibit specific protein targets - Increase or decrease gene transcription

3 types of cell surface receptors?

* Ion channels coupled receptors * G-protein coupled receptors * Enzyme-linked receptors

A nicotinic acetylcholine receptor is\_\_\_

an ionictropic receptor

A muscarinic acetylcholine receptor is \_\_\_\_

a metabotropic receptor

Enzyme-linked receptors\_\_\_\_

dimerize to form catalytic domains

Common Second Messangers:

* cAMP * cGMP * DAG (diacylglycerol) * IP3 (inositol triphosphate)

cAMP

activates protein kinase A (PKA)

cGMP

Activates protein kinase G (PKG) and opens cation channels in rod cells

DAG

activates protein kinase c (PKC)

IP3

Opens ca2+ cannels in the ER

What are the two forms of molecular switches in singaling?

- signaling by phosphorylation - signaling by GTP binding

A intracelllular signaling protein is ON when it's ____ or bound to\_\_\_\_. It's OFF when it's ____ or \_\_\_\_

ON- phosphorylated or bound to GTP OFF- dephosphorylated or bound to GDP

protein kinases ___ a phosphate from \_\_\_

remove a phosphate from ATP and add it to the intracellular signaling protein

protein phosphatases ____ the intracellular signaling protein

dephosporylate (remove a phosphate)

GEF proteins-

-help GTP to bind by ejecting GDP

GAP

cuts of the terminal phosphate of GTP (Deposphorylates it to GDP)

Tyrosine Kinase receptors

-add phosphate from ATP to tyrosine residues

Which amino acid side chains get phosphorylated?

Tyrosine (Y), Serine (S), Threonine (T)

Signal integration

Multiple signals and their receptors can affect the same intracellular signaling molecule

What are the three types of intracellular signaling complexes?

* preformed signaling complex on a scaffold protein * assembly of signaling complex on activated receptor * assembly of signaling complex on phosphoinositide docking sites

What signaling pathway involves all three types of intracellular signaling complexes?

The insulin signaling complex

Receptor sequestration

Receptor down-regulation

receptor inactivation

Inactivation of signaling protein

Production of inhibitory protein

General G-protein activation

G-protein coupled receptors (GPCRs)

* Seven transmembrane domains * Responds to very diverse ligands – Photons – Peptide hormones – Eicosanoids – Amino acid derivatives • Largest family of cell surface receptors in eukaryotes – \>1,000 devoted to smell alone in mice • About half of all known drugs work through Gprotein coupled receptors

For GPCRs the C-terminus is on the ____ side and the N-terminus is on the ____ side.

C=cytosolic side N=extracellular side

The βγ subunit...

function as a unit and has never been shown to be separate in the cell.

The α-subunit is....

postranslationally modified by the addition of myristic acid to the N-terminus.

The γ-subunit is....

postranslationally modified by the addition of a polyisoprenoid, usually farnesyl.

These hydrophobic modifications (to the βγ subunit)...

serve to localize the complex to the membrane, its site of action.

the α-subunit has...

A ras domain and an AH (alpha-helical) domain

On a G-protein, the gdp binding spot is on the ___ subunit

alpha

β-adrenergic receptor is a...

G-protein coupled receptor

G-protein effectors:

* Ion channels * Adenylyl cyclase * Phospholipase Cβ * cGMP Phosphodiesterase

Adenylyl cyclase produces \_\_\_\_\_

cAMP

The ___ subunit of G-protein interacts with adenylate cyclase

Adenylate kinase has ___ catalytic domains.

How does cAMP produce a cellular response?

It binds to a protein kinase (PKA)

Activated PKA bind to ____ to produce\_\_\_

inactive CREB, CREB -binding protein (CBP)

CBP binds to \_\_\_

cyclic AMP response element (CRE) which activates a target gene for transcription

Acute response of cAMP

-phosphorylation of protein involves in glycogen metabolism

Delayed response of cAMP

- increase in synthesis of the somatostatin gene

Ser/Thr protein phosphatases ____ the action or protein kinases

reverse

Four types of protein phosphatases

-Type I (dephosphorylates most PKA substrates) – Type IIA (broad specificity, main PPTase) – Type IIB (aka Calcineurin, regulated by Ca2+) – Type IIC (minor player)

G-protein activation of PLCβ

• Phospholipase C beta ## Footnote * PLCβ is activated by specific Gα-subtypes * Gqα, Goα, and Goβγ activate PLC

Phosphatidylinositides

- phospolipase release IP3 from glycerol back bone, forming IP3 and diacylglycerol - diacylglycerol (DAG) activates PKC - IP3 releases ca2+ from the ER

Calcium is sometimes used as a \_\_\_\_

second messenger

Positive and negative feedback produce \_\_\_\_

calcium waves

Ca2+ homeostasis is maintained by...

* Membrane pumps: * Na+ driven Ca2+ exchanger * Ca2+ Pump

What three mechanism help to maintain low cytosolic Ca2+ levels?

* Ca2+ pump in ER membrane * Ca2+ binding molecules in the cytoplasm * active Ca2+ import into the mitochondria

Ca2+ signaling effects are mediated by which three Ca2+ binding proteins?

* Troponin C * Synaptotagmin * Calmodulin

Troponin C

– Muscle contraction

Synaptotagmin

– Neurotransmission

Calmodulin

– Multipurpose Ca2+ receptor involved in many responses – Binds 4 Ca2+ ions, need two or more or adopt an active conformation

How does Calmodulin change conformation upon Ca2+ binding?

Its two domains wrap around its target protein

What are the three types of Ca2+-Calmodulin-dependent protein kinases?

* Narrow Substrate specificity * Myosin light chain kinase (smooth muscle contraction) * Phosphorylase kinase (glycogen breakdown) * Broad substrate specificity * CaM-Kinase II

What does activated CaM kinase II do?

* Its mechanism of activation allows past calcium influxes to be “remembered” * The enzyme also changes its activity in response to calcium oscillations – It can react to frequency and amplitude of calcium spikes • Important for learning an memory in the brain

\_\_\_\_\_ can sense Ca2+ oscillations

CaM kinase II