Ah. West et al., CRYSTAL-STRUCTURE OF THE CATALYTIC DOMAIN OF THE CHEMOTAXIS RECEPTOR METHYLESTERASE, CHEB, Journal of Molecular Biology, 250(2), 1995, pp. 276-290
Signaling activity of bacterial chemotaxis transmembrane receptors is
modulated by reversible covalent modification of specific receptor glu
tamate residues. The level of receptor methylation results from the ac
tivities of a specific S-adenosylmethionine-dependent methyltransferas
e, CheR, and the CheB methylesterase, which catalyzes hydrolysis of re
ceptor glutamine or methylglutamate side-chains to glutamic acid. The
CheB methylesterase belongs to a large family of response regulator pr
oteins in which N-terminal regulatory domains control the activities o
f C-terminal effector domains. The crystal structure of the catalytic
domain of the Salmonella typhimurium CheB methylesterase has been dete
rmined at 1.75 Angstrom,resolution. The domain has a modified, doubly
wound alpha/beta fold in which one of the helices is replaced by an an
ti-parallel beta-hairpin. Previous biochemical and mutagenesis data su
ggest that the methylester hydrolysis catalyzed by CheB proceeds throu
gh a mechanism involving a serine nucleophile. The methylesterase acti
ve site is tentatively identified as a cleft at the C-terminal edge of
the beta-sheet containing residues Ser164, His190 and Asp286. The thr
ee-dimensional fold, and the arrangement of residues within the cataly
tic triad distinguishes the CheB methylesterase from any previously de
scribed serine protease or serine hydrolase.