Elucidation of the multiple roles of CheD in Bacillus subtilis chemotaxis

Abstract

Summary Chemotaxis by Bacillus subtilis requires the CheD protein for proper function. In a cheD mutant when McpB was the sole chemoreceptor in B. subtilis, chemotaxis to asparagine was quite good. When McpC was the sole chemoreceptor in a cheD mutant, chemotaxis to proline was very poor. The reason for the difference between the chemoreceptors is because CheD deamidates Q609 in McpC and does not deamidate McpB. When mcpC-Q609E is expressed as the sole chemoreceptor in a cheD background, chemotaxis is almost fully restored. Concomitantly, in vitro McpC activates the CheA kinase poorly, whereas McpC-Q609E activates it much more. Moreover, CheD, which activates chemoreceptors, binds better to McpC-Q609E compared with unmodified McpC. Using hydroxyl radical susceptibility in the presence or absence of CheD, the most likely sites of CheD binding were the modification sites where CheD, CheB, and CheR carry out their catalytic activities. Thus, CheD appears to have two separate roles in B. subtilis chemotaxis - to bind to chemoreceptors to activate them as part of the CheC/CheD/CheYp adaptation system and to deamidate selected residues to activate the chemoreceptors and enable them to mediate amino acid chemotaxis.

Borrelia burgdorferi CheD Promotes Various Functions in Chemotaxis and the Pathogenic Life Cycle of the Spirochete

“…CheD interacts with MCP3 and MCP4. To determine if CheD is able to modify a B. burgdorferi chemoreceptor MCP protein, we performed deamidation assays using recombinant purified proteins, as described previously (29,31). Even though we were able to detect deamidation with the positive-control (B. subtilis chemoreceptor) MCP-A, our multiple attempts under various assay conditions failed to deamidate any B. burgdorferi MCP.…”

“…In B. subtilis, CheD plays an important role in chemotaxis by modification of MCPs by deamidation of glutamine to glutamate residues or by enhancing CheC phosphatase chemotaxis activity to efficiently dephosphorylate the response regulator CheY, thereby regulating the levels of CheY-P (27-30). Because of its possession of the conserved residues, we predicted that B. burgdorferi CheD may exhibit functions similar to those seen in other bacteria (27,29,31). The B. burgdorferi genome lacks a homolog of the CheC gene but encodes a functional phosphatase, CheX, that efficiently dephosphorylates CheY3-P (33, 34).…”

“…It is noteworthy that the "flex" of B. burgdorferi is considered to be equivalent to the tumbling phenotype seen in E. coli. Moreover, the MCPs of B. burgdorferi contain the well-conserved potential substrate-binding sites of CheD (29,31,35). These observations led us to hypothesize that CheD in B. burgdorferi plays a role similar to that of its counterpart in B. subtilis.…”

“…CheD modifies the MCPs by deamidating glutamine to glutamate residues. The deamidation by CheD is required for the B. subtilis chemoreceptors to effectively transduce signals to the CheA kinase (29,31). Additionally, CheD interacts with the phosphatase CheC, enhancing its enzymatic activity and fine-tuning the intracellular concentration of CheY-P (27,29).…”

Internal Sense of Direction: Sensing and Signaling from Cytoplasmic Chemoreceptors

“…The second alternative system relies on the CheD and CheC proteins. Both of these proteins have enzymatic activity but additionally perform adaptation via protein-protein interactions (39). CheD interacts directly with chemoreceptors at the methylation region and can deamidate them, thereby increasing their ability to activate CheA (39).…”