Involved in chemotaxis. Part of a chemotaxis signal transduction system that modulates chemotaxis in response to various stimuli. Catalyzes the demethylation of specific methylglutamate residues introduced into the chemoreceptors (methyl-accepting chemotaxis proteins or MCP) by CheR. Also mediates the irreversible deamidation of specific glutamine residues to glutamic acid. [protein]-L-glutamate 5-O-methyl ester + H2O = H(+) + L-glutamyl-[protein] + methanol H2O + L-glutaminyl-[protein] = L-glutamyl-[protein] + NH4(+) Contains a C-terminal catalytic domain, and an N-terminal region which modulates catalytic activity. Phosphorylated in vitro by CheA2, but not by CheA1. Phosphorylation of the N-terminal regulatory domain activates the methylesterase activity. R.sphaeroides does not have a cheB in its group 1 operon. Part of the third chemotactic pathway (cheOp3); there are 3 operons encoding multiple homologs of the chemosensory proteins in R.sphaeroides. This locus, and cheB2, are essential for chemotaxis. CheB2 is not involved in phototaxis signaling. This protein is able to partially complement an E.coli cheB deletion mutant. Belongs to the CheB family.