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 18.104.22.168) 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 . 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
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.
January 2002 / First entry.
PROSITE method (with tools and information) covered by this documentation:
Simms S.A. Keane M.G. Stock J.
Multiple forms of the CheB methylesterase in bacterial chemosensing.
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