Bacterial Flagella and Chemotaxis II

Is the flagella and chemotaxis system assembly tightly regulated?

Yes it is

What does flagella assembly require simply?

Several genes and regulators

For the rod, hook, junction and filament assembly what do the proteins go through? (what are the folded proteins pushed through)

The export apparatus

What does the export apparatus look like?

Type 3 secretion system (T3SS)

When is the flagella going to be synthesized?

When it needs to swim towards or away from something

What does E.Coli 0157 use?

Type 3 secretion system to push proteins into a host cell and to subvert a hosts processes to cause an infection

What is a type 3 secretion system believed to have been derived from?

Flagella

From what direction is the flagella made?

From the bottom up. C ring and then P ring.

What is chemotaxis?

It is directed movement of organisms according to signals perceived in their environment

What are two types of signals for chemotaxis?

1. Chemoattractant

2. Chemorepellents

What are chemoattractants? What are some examples?

They are typically food and are good for the cell. Can be sugars, amino acids, or electron acceptors.

What are chemorepellents? What are some examples?

They are typically poisons and are bad. Can be alcohols, urea, extremes of pH, and low oxygen.

What does a counter clockwise rotation (CCW) cause?

The flagella will perform a RUN (swim). It will swim towards something that is good or away from something bad.

What does a clockwise rotation (CW) cause?

The flagella will tumble (reorientation). All the flagella will get pushed out and then clump together

What is the default setting of flagella?

A tumble (it is searching for something)

How do bacteria move? Is the direction of a new run random or predicted?

With long runs and short tumbles. Random

Are tumbles or runs more frequent?

Runs are more frequent if the cell encounters a positive change of attractant or a negative change of repellent

What are runs in the context of?

A concentration gradient of an environment

What are chemoreceptors (MCPs)?

They are methyl-accepting chemoreceptor proteins that can sense attractants or repellents either directly or indirectly via periplasmic binding proteins

Describe the structure of MCPs

They have a transmembrane component connecting the cytosolic component and extracellular component

Describe how MCPs work simply

1. Chemoreceptors are sensing the environment and will eventually bind a chemoattractant or repellent

2. This will cause a signal to be sent through the cytoplasmic membrane to the cytosolic component

3. Signalling cascade is then initiated

How is a stimulus response controlled by flagella?

1. Input signals are sensed by MCPs

2. Output response which is flagella movement

How is the input and output response linked?

Through signal transduction

What are two-component systems? What are they commonly used for? What do they allow for?

They are a common signalling cascade that are widely used for signal transduction in bacteria. They allow for phosphotransfer reactions

What does the first component of the TCS do?

It senses the input stimuli and is the chemoreceptor

What is on the cytoplasmic side of the chemoreceptor?

A kinase which will autophosphorylate itself and transfer the phosphate to the response regulator, which is the output. The response regulator will trigger the rotation of the flagella.

What activates the signalling cascade?

The phosphate transfer

When bacteria are sensing their environment what can they choose to do?

Phosphorylate or not

Are TCS phosphotransferase tightly regulated?

Yes

Do many pathways use TCSs?

Yes but each component is specific, there is no cross talk among them

What is CheA?

It is the histidine kinase on the cytoplasmic side of the chemoreceptor

What is CheW?

It is a linking protein that binds CheA to the chemoreceptor

What does CheA do?

It phosphorylates itself by taking the phosphate group from ATP and then transfers it to CheY

What is CheY?

It is the response regulator

What happens once CheY is phosphorylated?

It will shuttle itself to the cytoplasm portion of the flagella and link to it to form a clockwise rotation in the flagella (causes a tumble)

What happens when CheY is not phosphorylated?

It will cause a counterclockwise rotation in the flagella (causes a run)

What does FliM bind to?

CheY binds to FliM if phosphorylated which triggers FliG and causes interaction with the Mot proteins to change their conformation

What is the whole point of the chemotaxis pathway?

To sense if there is an attractant or not and if there is then the phosphorylation cascade is not activated and runs will be performed