The response regulator CheB functions within the bacterial chemotaxis system together with the methyltransferase CheR (see <PDOC50123>) to control the level of chemoreceptor methylation, influencing the signaling activities of the receptors. Like many members of the response regulator family, CheB has a multidomain architecture. It consists of an N-terminal phosphoaccepting regulatory domain with a conserved fold containing the site of phosphorylation, a single conserved aspartate residue (see <PDOC50110>), and a C-terminal effector domain joined by a linker region. The effector domain is a methylesterase (EC 3.1.1.61) that catalyses the hydrolysis of γ-carboxyl glutamyl methyl esters in the cytoplasmic domain of chemoreceptor proteins [1,2]. The CheB methylesterase domain belongs to the class of serine hydrolases that contain active site catalytic triads consisting of serine, histidine and aspartate residues [3]. Inhibition of methylesterase activity in intact unphosphorylated CheB is due to partial occlusion of the active site by the regulatory domain, thereby restricting access of the substrate chemoreceptors. The phosphorylation of the regulatory domain results in reorganization of the domain interface, allowing exposure of the active site to the receptor substrate [4,5].

The crystal structure of the Salmonella typhimurium CheB methylesterase has been solved. The structure of the CheB methylesterase domain is composed of six α-helices and nine β-strands with an overall α/β fold common for globular proteins that can be classified as a slight variation of a doubly wound α/β domain. The core of the molecules consists of a seven-stranded parallel β-sheet and is flanked by three α-helices on one side and three α-helices plus an antiparallel β-hairpin motif on the opposite side of the sheet [3,4].

The profile we developed covers the entire CheB methylesterase domain.