Question

What happens attractant is present but the Methyl-accepting chemotaxis proteins are mutagenized in a such way that they cannot by methylized?

Answer 1

In methyl accepting chemotaxis, methyl accepting chemotaxis protein (MCP) initiates a signal transduction pathway when encountering an attractant. MCPs are chemotaxis receptors that are bound to histidine kinase CheA. CheW is involved in this interaction between MCP and CheW. ATP undergoes hydrolysis and induces phosphorylation of CheA. As a result of phosphorylation of CheA, there is activation of CheB and CheY, which are two response regulators by phosphorylation. CheB undergoes phosphorylation and activates its effector domain. CheR, a methyltransferase will methylate the four glutamate residues present on receptor cytoplasmic domain of MCP. CheY phosphorylation will lead to the modulation of the motor of the flagella. The motor switch apparatus is docked. This results in clockwise rotation of the flagella, thereby controlling the direction of rotation of the flagella motor. The clockwise flagella rotation is involved in tumbling characteristic of bacteria movement.

The inhibition of chemotaxis can occur if the CheB-phosphorylated molecule will demethylates the same glutamate residues on MCP. Thus, CheB phosphorylation is inhibitory to this pathway, while CheY phosphorylation will induce flagella chemotaxis to the attractant.

CheY and CheB can be autodephosphorylation to inhibit signaling. Further, dephosphorylation of CheY is enhanced by CheZ phosphatase.

If the MCP cannot undergo methylation after ATP hydrolysis and phosphorylation by CheA, then no chemotaxis is observed towards the attractant. There will be methylation of CheA and therefor no activation and phosphorylation of effector domain ChB and CheY. Hence, CheY cannot modulate flagellar motor towards the counterclockwise direction. Thus, bacterial cells will not move towards the attractant and will continue their clockwise movement.