Lecture 15: Metabotropic Signaling

What are the three steps to non-ionotropic signaling?

* When NT binds, it causes a change in the shape of the receptor
* This can activate an enzyme or g-protein
* sets off a chemical signaling cascade

What is the effector protein in the G(s) pathway?

Adenylyl cyclase

What is the second messenger in the G(s) pathwaay?

cAMP

What is the later effectors in the G(s) pathway?

Protein kinase A

What is the target action of the G(s) pathway?

increase protein phosphorylation

What are the three distinct subunits of G-protein and what does that make it called?

alpha, beta, and gamma → heterotrimeric (three different subunits)

What happens when the G9(s) receptor is not activated?

GDP (2 phosphates) is bound to the alpha subunit

When GDP is bound, is the G-protein is….

turned off

When GTP is bound to the alpha subunit, the G-protein…

is turned on

What happens when the NT binds with the g protein?

it causes the GDP to be exchanged for GTP (three phosphates) on the alpha subunit

What is the time limit of the G-protein pathway?

When the two complexes finish, the GTP is hydrolyzed back to GDP (via GAP action)

What does a regulator of g-protein signaling do? Give an example

Ex: GAP → It can continue the activation of the g-protein pathway or it can shut it down (GAP shuts it down)

What does adenylyl cyclase do?

produces second messengers

What are the proteins activated by the G-protein? What do they do?

– Adenylyl cyclase

– Phospholipase C

They activate the second messengers

What are second messengers? What do they do?

Molecules that relay signals from receptors on the cell surface to target molecules inside the cell → Activate protein kinases

What are some examples of second messengers? What do they do?

\-Calcium

– Cyclic nucleotides (cAMP)

– Diacylglycerol & IP3

Activate protein Kinases

What kind of interaction does ATP and cAMP have?

Their interaction results in amplification (like a high five)

What kind of interaction does cAMP and kinase have? What does that mean?

handshake, which means it does not result in amplification

Cyclic nucleotides

ATP converted to cyclic AMP, which can act on its own (e.g., binding to ligand-gated ion channels) or activate protein kinase A (PKA)

How do you turn off or inactivate cAMP? What is that considered?

the phosphodiesterase go around and eat up the cAMP to inactivate it. It’s the “time limit”

Protein Kinase

These act to phosphorylate target proteins, causing changes in conformation and activation

What happens when protein kinase sticks a phosphate on another protein?

Changes the shape and action of the protein

What is the time limit of a phosphoprotein?

phosphodiesterase go around and knock the phosphates off

What do Catalytic domains or subunits do?

stick to the phosphates on the proteins

What do regulatory domains do? What stops them from doing their job?

They hold the catalytic domains, keeping them from sticking to the phosphates. However, when cAMP binds with the regulatory domains, they open up and release the catalytic domains

What does nuclear signaling do?

* Promotes synthesis of new RNA and protein
* Transcription factors aid in RNA transcription

The most long-term effects of intracellular messengers are due to…

nuclear signaling

What, in relation to nuclear signaling, can lead to long-term changes in the cell?

Protein kinases can activate transcription factors and lead to gene transcription

Promoter region of a gene

indicates where to start transcription

* some are the same across all cells (my hair is always brown)
* some are only activated at specific times (ex: only during development)

What does the transcriptional activator protein do?

Tells the cell when and where to start transcription

What is CREB?

It is a transcriptional activator protein for the g-protein

Phosphorylation of CREB…

increases gene transcription

How is CREB activated?

by many second-messenger pathways

What is the importance of c-fos?

We can’t put animals in an MRI machine so c-fos allows us to see which neurotransmitters were active during a certain activity

What can changes to gene transcription via second messenger pathways lead to?

* more or less nT production
* more or fewer receptor molecules produced and shipped
* More or fewer enzymes created to further produce signals
* Proteins that cause structural changes to the neuron can be turned on or off

What can increase synthesis of catecholamines (dopamine, norepinephrine, epinephrine)?

Electrical activity, neurotransmitter action, or even nerve growth factor (NGF)

What is the increase in synthesis of catecholamines caused by?

This is caused by phosphorylation of tyrosine hydroxylase

Where do electrical signals occur?

Within cells

Where do chemical signals occur?

between cells

What are the two advantages of chemical signaling?

signal amplification: 1 molecule can create tens of thousands of signals down the line (more than one change)

temporal control: some signaling cascades are fast, some are slow

What are the three reactions in the Gs process that cause amplification?

receptor → G-protein (can activate many g proteins)

adenylyl cyclase → cyclic AMP

Protein Kinases → phosphates transferred to target proteins

What are the two reactions in the Gs process that don’t cause amplification?

G-proteins → adenylyl cyclase (can only bind with one)

cyclic AMP → protein kinases (has to be bound to protein kinase in order to acivate)

What is the Gs pathway process?

norepinephrine → B adrenergic → adenylyl cyclase → cAMP → Protein Kinase → increase phosphorylation

What does the name protein kinase imply and what does that do?

Implies that we are sticking a phosphate group onto a protein which causes a change in the proteins shape and its job/pathway

What are the two heterotrimeric g-protein complexes and what happens when they finish their job?

Alpha-GTP and Beta-Gamma

When they are done, GTP is hydrolyzed back into GDP via GAP action and the g-protein trimer reforms in its inactive state/binds back to the receptor

What is the first messenger i the Gs pathway?

Neurotransmitter

Where can the second messenger move in the cell?

anywhere

What are the two things that cyclic AMP can do?

It can either activate protein kinase or open its gated channel

Why does cyclic AMP have to be turned off?

Because it binds to the protein kinase

How are phosphate groups removed?

They are removed by protein phostphates

How can protein kinases effect transcription?

They can activate transcription factors and lead to dene transcription, which can lead to long term changes in the cell

What leads to long lasting change in a cell?

building a new protein

Describe an example of protein kinase acting locally and acting long term in relation to gene transcription

locally: watching a scary movie and being jumpy for the night

long term: being in a constant state of fear will cause the protein kinase to travel to the nucleus via nuclear signaling and make new proteins, thus making that state of fear significantly more permanent

What reads off mRNA?

RNA polymerase

How does a cell know which gene to transcribe?

promotor region indicate when and where to start transcription

What is CREB?

protein that binds to the part of the DNA that is supposed to be read

What phosphorylates CREB so that we can begin transcription?

Protein Kinase