Sensory transduction in Escherichia coli : Role of a protein methylation reaction in sensory adaptation

Abstract

The behavioral response [chemitaxis] of E. coli to the addition of a stimulatory compound is transient; thus the organism undergoes sensory adaptation. When the compound is removed, E. coli undergoes the inverse process, called deadaptation, and very rapidly regains its sensitivity to the stimulus. The previously reported methylation of several cytoplasmic membrane proteins is correlated with, and very likely controls, the state of adaptation of the cell. In the absence of an added stimulus these proteins are methylated to a basal level. When the bacteria are stimulated by the addition of an attractant, the extent of methylation increases over a period of several minutes to a new level, which is maintained as long as the attractant is present. The magnitude of the increase in methylation is a function of the size of the stimulus and is directly proportional to the duration of the behavioral response. Upon removal of the attractant the level of methylation very rapidly falls to the basal value. Adaptation requires methionine, but maintenance of the adapted state and de-adaptation do not. Methylation requires methionine but maintenance of an attractant-induced level of methylation and the demethylation that occurs following removal of the attractant do not. A role for protein methylation in sensory adaptation is indicated.