CheC and CheD interact to regulate methylation of Bacillus subtilis methyl-accepting chemotaxis proteins

In this study, we have demonstrated that two unique proteins in Bacillus subtilis chemotaxis, CheC and CheD, interact. We have shown this interaction both by using the yeast two-hybrid system and by precipitation of in vitro translated products using glutathione-S-transferase fusions and glutathione agarose beads. We have also shown that CheC inhibits B. subtilis CheR-mediated methylation of B. subtilis methyl-accepting chemotaxis proteins (MCPs) but not of Escherichia coli MCPs. It was previously reported that cheC mutants tend to swim smoothly and do not adapt to addition of attractant; cheD mutants have very poorly methylated MCPs and are very tumbly, similar to cheA mutants. We hypothesize that CheC exerts its effect on MCP methylation in B. subtilis by controlling the binding of CheD to the MCPs. In absence of CheD, the MCPs are poor substrates for CheR and appear to tie up, rather than activate, CheA. The regulation of CheD by CheC may be part of a unique adaptation system for chemotaxis in B. subtilis, whereby high levels of CheY-P brought about by attractant addition would allow CheC to interact with CheD and consequently leave the MCPs, reducing CheA activity and hence the levels of CheY-P.