This family contains the methylesterase CheB (EC 188.8.131.52; also known as CheB methylesterase, chemotaxis-specific methylesterase, methyl-accepting chemotaxis protein methyl-esterase, or protein methyl-esterase) domain, a phosphorylation-activated response regulator involved in reversible modification of bacterial chemotaxis receptors. Signaling output of the chemotaxis receptors is modulated by CheB and methyltransferase CheR by controlling the level of receptor methylation. CheB family members may also contain an N-terminal regulatory (REC) domain, which blocks the active site of the C-terminal domain until it is phosphorylated, or a CheR domain; typically cheB and cheR occur in the same operon. Reversible methylation of transmembrane chemoreceptors plays an important role in ligand-dependent signaling and cellular adaptation in bacterial chemotaxis. Phosphorylated CheB catalyzes deamidation of specific glutamine residues in the cytoplasmic region of the chemoreceptors and demethylation of specific methyl glutamate residues introduced into the chemoreceptors by CheR.