Gs. Anand et al., ACTIVATION OF METHYLESTERASE CHEB - EVIDENCE OF A DUAL ROLE FOR THE REGULATORY DOMAIN, Biochemistry (Easton), 37(40), 1998, pp. 14038-14047
The response regulator CheB functions within the bacterial chemotaxis
system together with the methyltransferase CheR to control the level o
f chemoreceptor methylation, influencing the signaling activities of t
he receptors. CheB catalyzes demethylation of specific methylglutamate
residues introduced into the chemoreceptors by CheR. CheB has a two-d
omain architecture consisting of an N-terminal regulatory domain joine
d by a linker to a C-terminal effector domain. In the unphosphorylated
state of the response regulator, the regulatory domain inhibits the m
ethylesterase activity of the effector domain. Upon phosphorylation of
a specific aspartate residue within the regulatory domain, the C-term
inal methylesterase activity is stimulated, resulting in the subsequen
t demethylation of the chemoreceptors. We have investigated the mechan
ism of regulation of CheB activity by the N-terminal regulatory domain
. First, we have found that phosphorylation of the N-terminal domain n
ot only relieves inhibition of the C-terminal methylesterase activity
but also provides an enhancement of this activity above that seen for
the C-terminal effector domain alone. Second, we have identified mutat
ions in CheB that show an enhancement of methylesterase activity in th
e absence of phosphorylation. Most of these single-site mutations are
localized in the linker region joining the regulatory and effector dom
ains. On the basis of these observations, we propose a model for activ
ation of CheB in which phosphorylation of the regulatory domain result
s in a reorganization of the domain interface, allowing exposure of th
e active site to the receptor substrate and simultaneously stimulating
methylesterase activity.