Question

propose a mechanism by which chemotaxis is used by E. coli to move away from a repellent.

In particular, think about the following:

• Describe the interaction between the chemoreceptors and the two-component regulatory system when dealing with a repellent
• What kind of flagellar movement does this cause?
• How can the cell detect whether it’s moving away or towards a repellent in a gradient?

Answer 1

The chemotaxis signaling pathway of e coli-

• E. coli senses chemoeffector gradients by comparing current concentrations to those encountered over the past few seconds of travel.
• The E. coli has four transmembrane chemoreceptors, known as methyl-accepting chemotaxis proteins (MCPs).
• It has periplasmic ligand binding sites and conserved cytoplasmic signaling domains.
• MCPs record the cell's recent chemical past in the form of reversible methylation of specific glutamic acid residues in the cytoplasmic signaling domain.
• Whenever current ligand occupancy state fails to coincide with the methylation record, the MCP initiates a motor control response and a feedback circuit that updates the methylation record to achieve sensory adaptation and cessation of the motor response.
• A fifth MCP-like protein, Aer, mediates aerotactic responses by monitoring redox changes in the electron transport chain. Aer undergoes sensory adaptation through a poorly-understood, methylation-independent mechanism.

1. The five MCP-family receptors in E. coli utilizes cytoplasmic signaling proteins to control flagellar rotation and sensory adaptation.
2. CheW and CheA generate receptor signals; CheY and CheZ control motor responses; CheR and CheB regulate MCP methylation state.