Requirement of both kinase and phosphatase activities of an Escherichia coli receptor (Taz1) for ligand-dependent signal transduction.
Taz1 is a hybrid receptor in the Escherichia coli cytoplasmic membrane, consisting of the N-terminal ligand binding domain of Tar (a chemoreceptor for aspartate) and the C-terminal signaling domain of EnvZ (an osmosensor). The binding of aspartate to an extra cytoplasmic domain induces the transmembrane signal to the cytoplasmic signaling domain. The signaling domain functioning as a protein kinase evokes a response by transferring a phosphate from an intracellular histidine to OmpR. This domain also encodes an OmpR-specific phosphatase whose action is crucial in completing the OmpR phosphorylation cycle. Phosphorylated OmpR acts as a transcriptional activator for the ompC gene. A number of mutations were introduced into the signaling domain in conserved sequences of the prokaryotic histidine kinase family. All Taz1 mutants lost the ability to both autophosphorylate the histidine residue and transfer the phosphate to OmpR. These mutated receptors were unable to activate ompC-lacZ expression. However, ompC-lacZ was able to be activated by complementation of Taz1 mutants. In some combinations, two different defective Taz1 mutants could restore both OmpR kinase and phosphatase activities when co-expressed. In other combinations only kinase activity was restored. Aspartate-inducible ompC-lacZ expression was restored only in the former cases, while in the latter cases ompC-lacZ expression became constitutive. These results indicate that the kinase activity is essential to activate ompC expression while the phosphatase activity is required to regulate ompC gene expression in a ligand-dependent manner.
Yang
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Department of Biochemistry, Robert Wood Johnson Medical School University of Medicine and Dentistry of New Jersey, Piscataway 08854.
Inouye
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D001224:Aspartic Acid / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D004252:DNA Mutational Analysis; D004790:Enzyme Induction; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005816:Genetic Complementation Test; D008024:Ligands; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000235:genetics*; D011494:Protein Kinases / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D015398:Signal Transduction; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics
D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008024:Ligands; D011993:Recombinant Fusion Proteins; C072091:Taz1 protein, E coli; D001224:Aspartic Acid; D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases; D001616:beta-Galactosidase