Signal transduction and osmoregulation in Escherichia coli. A novel type of mutation in the phosphorylation domain of the activator protein, OmpR, results in a defect in its phosphorylation-dependent DNA binding

• Published in: The Journal of biological chemistry 1991-06, Vol.266 (17), p.10775-10780
• Main Authors: NAKASHIMA, K, KANAMARU, K, AIBA, H, MIZUNO, T
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - isolation & purification; Bacterial Outer Membrane Proteins - metabolism; Biological and medical sciences; Cytidine Triphosphate - metabolism; DNA-Binding Proteins - metabolism; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli - physiology; Escherichia coli Proteins; Fundamental and applied biological sciences. Psychology; Gene Expression; Kinetics; Molecular and cellular biology; Molecular genetics; Multienzyme Complexes; Phenotype; Phosphorylation; Signal Transduction; Transcription. Transcription factor. Splicing. Rna processing; Water-Electrolyte Balance
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)99085-X

The transcriptional factors, OmpR and EnvZ, are crucially involved in the osmotic regulation of ompF and ompC expression in Escherichia coli. The DNA binding ability of the positive regulator, OmpR, is modulated through its phosphorylation and dephosphorylation mediated by EnvZ in response to the medium osmolarity. In this study, two examples of a novel type of mutant ompR allele, ompR96A and ompR115S, whose phenotype is OmpF- OmpC- irrespective of the medium osmolarity, were characterized. These mutations result in amino acid conversions, Glu96 to Ala and Arg115 to Ser, respectively, within the phosphorylation domain of OmpR. Nevertheless, these mutant proteins were capable of undergoing phosphorylation and dephosphorylation normally, just like wild-type OmpR. However, the phosphorylation-dependent enhancement of their in vitro DNA binding ability was found to be severely affected. It was thus revealed that these mutant OmpR represent a novel type in terms of the mechanism of phosphorylation-dependent activation of the function of OmpR, i.e. those are normally phosphorylated but not activated to bind to the cognate promoter DNAs. In this respect, it was further suggested that OmpR oligomerization may be involved in the mechanism underlying the phosphorylation-dependent enhancement of the DNA binding ability of OmpR. The mutant proteins characterized in this study seem to be defective in this particular oligomerization process observed in vitro.