Demethylation of bacterial chemoreceptors is inhibited by attractant stimuli in the complete absence of the regulatory domain of the demethylating enzyme

The CheB methylesterase catalyzes the demethylation of membrane receptors during chemotaxis in Salmonella typhimurium. The kinetic properties of the full length product of the cheB gene are compared to those of the isolated C-terminal catalytic domain. The fragment has at least a 15-fold higher specific activity than the intact protein. In intact cells receptor demethylation is inhibited by attractants such as L-aspartate. We show here that both forms of the enzyme are similarly inhibited in vitro. Thus, the C-terminal catalytic domain of the CheB protein is sufficient for this aspect of esterase regulation. Inhibition by attractants appears to be caused by changes in receptor conformation rather than by changes in the activity of the demethylating enzyme.