Bacterial Flagella and Chemotaxis III

Are there many parts of regulation for CheA?

Yes there is

What does the kinase domain on the bottom of the MCP do?

It is where information is transferred to based on what it sees in the environment. It can then decide if it wants to phosphorylate itself or not

What does the transmembrane do?

it links the perceived signal in the environment to the kinase activity (kinase control)

What is the default setting for kinase activity?

It wants to phosphorylate itself all the time which results in a tumble

What happens if the sensing domain of the MCP sees an attractant or repellent?

The kinase activity will be shut off resulting in a run

What is CheA? What does it do?

It is a histidine kinase that is attached to MCPs in the cytoplasm. It uses ATP to autophosphorylate and can transfer the phosphate to CheY the response regulator

What can be found on the bottom portion of MCPs in the cytoplasm?

Methylation sites that help in the fine tuning of the signal being produced

Can different pathways use the same response regulator or histidine kinase complex?

Yes but the components of the signalling cascade are specific for each process

What can different MCPs on the surface do?

They can cluster together and signal through CheA and CheY

What does CheY do?

It is the response regulator and accepts phosphates from CheA

What happens if CheY does not have a phosphate?

Counterclockwise rotation = run

What happens if CheY has a phosphate?

Clockwise rotation = tumble

What does CheY-P bind to?

FliM which is the motor switch in the C-ring.

What does FliM associate with?

It is directly connected to FliG which has a tight interaction with the Mot proteins in the cytoplasmic membrane

In order for bacteria to respond to its environment what do bacteria have to recognize? How can this be done?

A concentration gradient which can only be done if bacteria have a mechanism that triggers a memory

What is memory called in bacteria?

Sensory adaptation

If you are swimming towards something what do you have to recognize?

If the compound has already been there and if you are swimming towards more of it or not.

What are the 3 mechanisms used by chemoreceptors to recognize compounds (3 levels of control for chemotaxis)?

1. CheA kinase activity

2. Motor control

3. MCP sensory adaptation

What is CheA kinase activity dependent on? What is it?

1. Receptor clustering

2. Attractant or repellent binding

On and off of the Che kinase activity

What is motor control dependent on?

1. CheY phosphorylation vs

2. Dephosphorylation by CheZ

What is MCP sensory adaptation dependent on? What is it?

1. CheR methylation vs

2. CheB demethylation

MCP sensory adaptation is the responsiveness to signal

When is CheA inhibited (kinase activity turned off)? What happens to CheY-P levels?

In the presence of an attractant. They start to decrease and have less tumbles and longer runs. bacteria will swim towards an attractant

When is CheA activated (kinase activity turned on)? What happens to CheY-P levels?

In the absence of an attractant or when stimulated by a repellent. CheY-P levels will increase making tumbles more frequent as they search for food or move away from a repellent

What is CheA? What binding protein does it have?

It is a histidine kinase linked to MCPs with the CheW binding protein

How does CheA autophosphorylate?

By using ATP

Is CheA active as a dimer? When is it more efficient?

Yes but more efficient as trimers of dimers (higher kinase activity)

What is CheA kinase activity based on?

Clustering of receptors (dont all have to be the same)

Why do we need motor control?

Need something to take away the phosphate so it can respond again (chemotaxis response can still occur). If we didn’t have this then it would be an inefficient pathway

What does CheZ do?

It dephosphorylates the CheY in a reaction that is essential to maintain a continuous chemotactic response to environmental changes.

What is CheZ?

It is a phosphatase that decreases levels of CheY-P to regenerate CheY

Aside from maintaining a chemotactic response, what is motor control essential for?

The readjustment of bacterial behaviour.

What do CheR/CheB activity control?

MCP responsiveness to signals

How can MCPs recognize concentration gradients?

The MCP has areas where it can be methylated and demethylated

If you want to perceived something you’ve already seen before, what do you have to do?

Dampen the signal (decrease intensity of the signal)

Are phosphorylation cascades or methylation events faster?

Phosphorylation cascades

What does CheR activity do?

It will slowly methylate MCPs which cause them to become more unresponsive to the signal

What does methylation eventually lead to?

The activation of CheA

Why do we need to become unresponsive to the signal?

This is because we need to become less sensitive to the attractant in order to still be able to swim towards higher concentrations of it after the initial activation. It can do this because it has been methylated.

What is CheB activity?

It slowly demetheylates MCPs allowing them to become more responsive to the signal.

When is CheB active?

Only after CheA phosphorylation

What does activation of CheA through methylation cause?

Tumbles even if your in the perfect direction for the concentration gradient

What does this activation of CheA through methylation serve as?

1. Tumble is a double check

2. This is how bacteria make memory

Does CheB get phosphorylated?

Yes it does

Overall what does sensory adaptation allow for?

To remember what it just saw a few seconds ago and to create bacterial memory