title: Active site of the enzyme which demethylates receptors during bacterial chemotaxis.
abstract: The CheB methylesterase catalyzes the hydrolysis of glutamyl methyl esters in bacterial chemoreceptor proteins. Studies with residue-specific inhibitors suggest that a cysteine residue is required. The nucleotide sequence of the cheB gene predicts a 349-amino acid protein with cysteine residues at positions 207 and 309. Oligonucleotide-directed mutagenesis was used to change each cysteine to an alanine. Whereas the Cys207-Ala mutation had essentially no effect on esterase activity, the Cys309-Ala mutation caused a complete inactivation of the enzyme. Cys309 is located adjacent to a sequence of amino acids which is characteristic of the beta-alpha-beta motif found in a number of nucleotide binding proteins associated with receptor function in vertebrate tissues. A central feature of this structure is Gly-X-Gly-X-X-Gly. Mutation of the second glycine in this region (Gly284) to a valine also caused a complete loss of esterase activity.
mesh_terms: D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002628:Chemoreceptor Cells / Q000378:metabolism; D002633:Chemotaxis; D003545:Cysteine; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics; D008623:Mercaptoethanol / Q000494:pharmacology; D009154:Mutation; D012486:Salmonella typhimurium / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D008623:Mercaptoethanol; D004228:Dithionitrobenzoic Acid; D002265:Carboxylic Ester Hydrolases; C041144:chemotactic protein methylesterase; D003545:Cysteine