Chemotaxis

How is chemotaxis carried out?

By a series of signal transduction events

Methyl-accepting chemotaxis proteins (MCPs)

transmembrane sensory proteins

Chemotaxis process involving methyl-accepting chemotaxis proteins (MCPs)

1. Presence of attract or repellent is first sensed by transmembrane sensory proteins called Methyl-accepting chemotaxis proteins (MCPs).

2. MCPs interact with cytoplasmic protein CheW, and modulate the level of autophosphorylation of the CheA sensor kinase (attracts decr level of phosphorylation, repellants increase level of autophosphorylation).

3. Phosphorylated CheA (CheA-P) transfers the phosphoryl group to the response regulator CheY

CheY-P differs from other response regulators. How?

It doesn’t influence transcription of a gene, but rather deermine direction of flagellar rotation.

Regulation of chemotaxis and adaptation involving methylation

1. Protein CheR can methylate MCPs. 

2. Another protein, CheB, is phosphorylated by CheA-P, and CheB-P is able to demethylate MCPs.

3. In the presence of a continually high level of attract = lower lvl of CheA-P, CheY-P, CheB-P, level of methylation will increase b/c of lack of CheB-P mediated demethylation

The level of methylation of MCPs will affect their sensitivity to the attractant or repellant. How?

Fully methylated MCPs are not able to respond to attractant, resulting in, eventually, the phosphorylation of CheA and subsequent phosphorylation of CheB & demethylation of MCP

What is chemotaxis?

Complex bacterial behaviour modulated by shifts in protein activity. Modified 2-component regulatory systems.

Chemotactic bacteria can do what?

Sense changes in chem gradients over time

Changes in chemical gradients induce what in chemotactic bacteria?

Induce altered direction and duration of flagellar rotation, leading to directed movement over time.

Study of chemotaxis using mutants

• How do you study these microbes?

• How do the microbes behave?

Isolated using a capillary tube filled with nutrients. Microbes with normal chemotaxis will move into the tube, those with mutations in chemotactic proteins will remain outside the tube.

3 steps of chemotaxis

1. response to signal

2. control of flagella rotation

3. adaptation

Response to signal - chemotaxis

Step 1: MCPs sense specific attractants/repellants, initiates signal transduction (or not)

Controlling flagella rotation - chemotaxis

Step 2 - CheY protein. Phosphorylated by CheA-P when attracts low. CheY-P initiates flagella reversal (tumbling)

Adaptation - chemotaxis

Step 3 - feedback loop. Allows the system to “reset” itself, allows temporal detection of signal concentration, requires modification of MCPs by methylation

Che proteins

2 component regulatory system

What do CheA and CheY do? i.e. how do they work together?

CheA works as sensor kinase, becoming phosphorylated. CheA then phosphorylates CheY (RR protein). CheY bind to the flagellar motor, changing its activity.

Methyl-accepting chemotaxis proteins (MCPs) also work in chemotaxis systems by doing what?

Interacting with CheW proteins, autophosphorylation of CheA is modulated. Attracts decrease phosporylation, repellants increase phosphorylation. Provide for longer sustained “runs” of directed motion when attractants are present

Methylation of MCPs also regulate attraction during periods of…? What does this mean and result in? (discuss sensitivity)

During periods of high attractant levels in a process known as “adaptation”. Highly methylated MCPs will only respond to very high levels of attractant. If very high levels are not maintained, phosphorylation of CheA/CheB will lead to eventual demethylation of MCP. Results in greater sensitivity to the attractant, helping the system “reset” and avoid saturation over time.