This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Salto, R. Articles by Ramos, J. L. Search for Related Content PubMed PubMed Citation Articles by Salto, R. Articles by Ramos, J. L. Pubmed/NCBI databases Compound via MeSH Substance via MeSH Hazardous Substances DB 3-NITROTOLUENE TOLUENE

 Previous Article  |  Next Article 

J Bacteriol, February 1998, p. 600-604, Vol. 180, No. 3
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Modulation of the Function of the Signal Receptor Domain of XylR, a Member of a Family of Prokaryotic Enhancer-Like Positive Regulators

Rafael Salto,^* Asunción Delgado, Carmen Michán, Silvia Marqués,^§ and Juan L. Ramos

Department of Biochemistry, Molecular and Cellular Biology of Plants, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, E-18008 Granada, Spain

Received 12 June 1997/Accepted 20 November 1997

The XylR protein controls expression from the Pseudomonas putida TOL plasmid upper pathway operon promoter (Pu) in response to aromatic effectors. XylR-dependent stimulation of transcription from a Pu::lacZ fusion shows different induction kinetics with different effectors. With toluene, activation followed a hyperbolic curve with an apparent K of 0.95 mM and a maximum -galactosidase activity of 2,550 Miller units. With o-nitrotoluene, in contrast, activation followed a sigmoidal curve with an apparent K of 0.55 mM and a Hill coefficient of 2.65. m-Nitrotoluene kept the XylR regulator in an inactive transcriptional form. Therefore, upon binding of an effector, the substituent on the aromatic ring leads to productive or unproductive XylR forms. The different transcriptional states of the XylR regulator are substantiated by XylR mutants. XylRE172K is a mutant regulator that is able to stimulate transcription from the Pu promoter in the presence of m-nitrotoluene; however, its response to m-aminotoluene was negligible, in contrast with the wild-type regulator. These results illustrate the importance of the electrostatic interactions in effector recognition and in the stabilization of productive and unproductive forms by the regulator upon aromatic binding. XylRD135N and XylRD135Q are mutant regulators that are able to stimulate transcription from Pu in the absence of effectors, whereas substitution of Glu for Asp135 in XylRD135E resulted in a mutant whose ability to recognize effectors was severely impaired. Therefore, the conformation of mutant XylRD135Q as well as XylRD135N seemed to mimic that of the wild-type regulator when effector binding occurred, whereas mutant XylRD135E seemed to be blocked in a conformation similar to that of wild-type XylR and XylRE172K upon binding to an inhibitor molecule such as m-nitrotoluene or m-aminotoluene.

---

^* Corresponding author. Present address: Department of Biochemistry and Molecular Biology, School of Pharmacy, University of Granada, E-18071 Granada, Spain. Phone: 34-58-246363. Fax: 34-58-248960. E-mail: rsalto{at}goliat.ugr.es.

Present address: Department of Microbiology and Molecular Genetics, University of California, Los Angeles, CA 90095-1489.

Present address: Department of Biochemistry, School of Veterinary Sciences, University of Córdoba, 14071 Córdoba, Spain.

^§ Present address: Department of Genetics, School of Biology, University of Seville, 41012 Seville, Spain.

This article has been cited by other articles:

• Guazzaroni, M.-E., Gallegos, M.-T., Ramos, J. L., Krell, T. (2007). Different Modes of Binding of Mono- and Biaromatic Effectors to the Transcriptional Regulator TTGV: ROLE IN DIFFERENTIAL DEREPRESSION FROM ITS COGNATE OPERATOR. J. Biol. Chem. 282: 16308-16316 [Abstract] [Full Text]  
• van Sint Fiet, S., van Beilen, J. B., Witholt, B. (2006). Selection of biocatalysts for chemical synthesis. Proc. Natl. Acad. Sci. USA 103: 1693-1698 [Abstract] [Full Text]  
• Tropel, D., van der Meer, J. R. (2004). Bacterial Transcriptional Regulators for Degradation Pathways of Aromatic Compounds. Microbiol. Mol. Biol. Rev. 68: 474-500 [Abstract] [Full Text]  
• Lessner, D. J., Parales, R. E., Narayan, S., Gibson, D. T. (2003). Expression of the Nitroarene Dioxygenase Genes in Comamonas sp. Strain JS765 and Acidovorax sp. Strain JS42 Is Induced by Multiple Aromatic Compounds. J. Bacteriol. 185: 3895-3904 [Abstract] [Full Text]  
• Jaspers, M. C. M., Suske, W. A., Schmid, A., Goslings, D. A. M., Kohler, H.-P. E., van der Meer, J. R. (2000). HbpR, a New Member of the XylR/DmpR Subclass within the NtrC Family of Bacterial Transcriptional Activators, Regulates Expression of 2-Hydroxybiphenyl Metabolism in Pseudomonas azelaica HBP1. J. Bacteriol. 182: 405-417 [Abstract] [Full Text]  
• Wise, A. A., Kuske, C. R. (2000). Generation of Novel Bacterial Regulatory Proteins That Detect Priority Pollutant Phenols. Appl. Environ. Microbiol. 66: 163-169 [Abstract] [Full Text]  
• O'Neill, E., Sze, C. C., Shingler, V. (1999). Novel Effector Control through Modulation of a Preexisting Binding Site of the Aromatic-responsive sigma 54-Dependent Regulator DmpR. J. Biol. Chem. 274: 32425-32432 [Abstract] [Full Text]