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J Biol Chem, Vol. 273, Issue 41, 26415-26420, October 9, 1998
From the Universität Osnabrück, Fachbereich
Biologie/Chemie, Abteilung
Mikrobiologie, D-49069 Osnabrück, Germany
Escherichia coli responds to
K+ limitation or high osmolarity by induction of the
kdpFABC operon coding for the high affinity K+-translocating Kdp-ATPase. KdpD, the sensor kinase of
this system, is a bifunctional enzyme catalyzing the
autophosphorylation by ATP and the dephosphorylation of the
corresponding response regulator KdpE. Here we demonstrate that
individual replacements of clustered arginine residues located close to
transmembrane domain TM4 modulate the ratio of kinase to phosphatase
activity. Thus KdpD-Arg511
Individual Substitutions of Clustered Arginine Residues of the
Sensor Kinase KdpD of Escherichia coli Modulate the Ratio
of Kinase to Phosphatase Activity
Gln is characterized by an
increase in the kinase activity and a loss of the phosphatase activity.
However, when Arg at position 511 is replaced with Lys, activities of
the corresponding protein are comparable with wild-type KdpD. In
contrast, replacement of arginine residues at positions 503, 506, or
508 with glutamine or lysine causes a decrease of the kinase and an
increase of the phosphatase activities. Changes of the activities of
these KdpD proteins correspond with alterations in kdpFABC
expression. Thus KdpD-Arg511 Gln causes constitutive
expression of kdpFABC. KdpD proteins with Arg replacements
at positions 503, 506, or 508 are unable to respond to osmolarity,
whereas the sensing of K+ limitation is not influenced.
Simultaneous replacement of arginine residues 508 and 511 or 506, 508, and 511 with glutamine leads to a decrease of the phosphatase activity.
However, kdpFABC expression is dependent on K+
and osmolarity. Finally, when Arg513 is replaced with
glutamine the amount of KdpD detected in the membrane is drastically
reduced. These results imply that there is an equilibrium between the
kinase and phosphatase activities of KdpD, which can be shifted by the
replacement of one arginine residue. An electrostatic switch mechanism
within the protein is proposed through which the ratio of kinase to
phosphatase is regulated. Finally, these results lend support to the
notion that KdpD can be activated by two distinct stimuli,
K+ limitation and osmolarity.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.
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