Differential CheR affinity for chemoreceptor C-terminal pentapeptides biases chemotactic responses

The capacity of chemotaxis pathways to respond to signal gradients relies on adaptation mediated by the coordinated action of CheR methyltransferases and CheB methylesterases. Many chemoreceptors contain a C-terminal pentapeptide at the end of a linker. In Escherichia coli, this pentapeptide forms a high-affinity binding site for CheR and phosphorylated CheB, and its removal interferes with adaptation. The analysis of all available chemoreceptor sequences showed that pentapeptide sequences vary greatly, and bacteria often possess multiple chemoreceptors that differ in their pentapeptide sequences. Using the phytopathogen Pectobacterium atrosepticum SCRI1043, we assessed whether this sequence variation alters CheR affinity and chemotaxis. SCRI1043 has 36 chemoreceptors, of which 19 possess a C-terminal pentapeptide. Using isothermal titration calorimetry, we show that the affinity of CheR for the different pentapeptides varies up to 11-fold ( K _D of 90 nM to 1 µM). The pentapeptides with the highest and lowest affinities differed only in a single amino acid. Deletion of the cheR gene abolishes chemotaxis. PacC is the sole chemoreceptor for L-Asp in SCRI1043, and the replacement of its pentapeptide with those having the highest and lowest affinities significantly interfered with L-Asp chemotaxis. Variable pentapeptide sequences thus provide a mechanism to bias the responses mediated by chemoreceptors.