Bacillus subtilis CheD is a chemoreceptor modification enzyme required for chemotaxis

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The chemotaxis system in Bacillus subtilis shares similarities with Escherichia coli but possesses unique genes like cheC and cheD, suggesting greater complexity.
• A cheD mutant in B. subtilis exhibits impaired chemotaxis, abnormal receptor methylation, and poor response to stimuli, highlighting CheD's importance.
• Homologs of CheD are widespread in bacteria and archaea, indicating a significant, yet uncharacterized, role in chemotactic sensory transduction.

Purpose of the Study:

• To elucidate the unknown molecular function of the Bacillus subtilis CheD protein.
• To investigate the specific enzymatic activity of CheD in the context of bacterial chemotaxis.

Main Methods:

• Enzymatic assays to determine the catalytic activity of purified CheD protein.
• Analysis of chemoreceptor modification in wild-type and cheD mutant strains of B. subtilis.

Main Results:

• CheD was demonstrated to catalyze the amide hydrolysis (deamidation) of glutaminyl side chains on the B. subtilis chemoreceptor McpA.
• Evidence was found that CheD also deamidates other B. subtilis chemoreceptors, McpB and McpC.
• Deamidation by CheD, not previously recognized as the primary mechanism, is essential for B. subtilis chemoreceptor signal transduction to the CheA kinase.

Conclusions:

• CheD's enzymatic activity is deamidation of specific glutaminyl residues on chemoreceptors.
• This deamidation by CheD is a critical and previously unrecognized step for signal transduction in Bacillus subtilis chemotaxis.
• The findings revise the understanding of chemotaxis regulation in B. subtilis and suggest broader implications for other organisms possessing CheD homologs.