Methylation, demethylation, and deamidation at glutamate residues in membrane chemoreceptor proteins.

Abstract

In bacteria, Chemotaxis toward attractants and away from repellents is mediated by a simple sensing system (for a recent review see Stock, 1987). Stimulatory ligands are detected through their interactions with specific receptors at the cell surface. Information from these peripheral chemoreceptor proteins is transduced into a signal that controls the activity of the flagellar motor so that cells move toward favorable environmental conditions. Six cytoplasmic proteins, the Che proteins, function in conjunction with the transmembrane chemoreceptors to control motility. These have been defined both biochemically and genetically. The corresponding che genes are located in two adjacent operons called Mocha and Meche: Open image in new window Two of the six proteins are enzymes that catalyze the reversible methylation of receptor glutamate residues. CheR transfers methyl groups from S-adenosylmethionine to these glutamate side chains, and CheB mediates the hydrolysis of the γ-carboxyl methylesters that are produced. This review will focus on the chemistry and enzymology of these and related receptor modification reactions.