Requirement of the cheB function for sensory adaptation in Escherichia coli

The chemotactic behavior of Escherichia coli mutants defective in cheB function, which is required to remove methyl esters from methyl-accepting chemotaxis proteins, was investigated by subjecting swimming or antibody-tethered cells to various attractant chemicals. Two cheB point mutants, one missense and one nonsense, exhibited stimulus response times much longer than did the wild type, but they eventually returned to the prestimulus swimming pattern, indicating that they were not completely defective in sensory adaptation. In contrast, strains deleted for the cheB function showed no evidence of adaptation ability after stimulation. The crucial difference between these strains appeared to be the residual level of cheB-dependent methylesterase activity they contained. Both point mutants showed detectable levels of methanol evolution due to turnover of methyl groups on methyl-accepting chemotaxis protein molecules, whereas the cheB deletion mutant did not. In addition, it was possible to incorporate the methyl label into the methyl-accepting chemotaxis proteins of the point mutants but not into those of the cheB deletion strain. These findings indicate that cheB function is essential for sensory adaptation in Escherichia coli.