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Journal of Bacteriology, August 2009, p. 5205-5215, Vol. 191, No. 16
0021-9193/09/$08.00+0     doi:10.1128/JB.00526-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Specific Interactions between Four Molybdenum-Binding Proteins Contribute to Mo-Dependent Gene Regulation in Rhodobacter capsulatus{triangledown}

Jessica Wiethaus,1 Alexandra Müller,1 Meina Neumann,2 Sandra Neumann,1 Silke Leimkühler,2 Franz Narberhaus,1 and Bernd Masepohl1*

Lehrstuhl für Biologie der Mikroorganismen, Fakultät für Biologie und Biotechnologie, Ruhr-Universität Bochum, 44780 Bochum, Germany,1 Molekulare Enzymologie, Institut für Biochemie und Biologie, Universität Potsdam, 14469 Potsdam, Germany2

Received 20 April 2009/ Accepted 28 May 2009

The phototrophic purple bacterium Rhodobacter capsulatus encodes two transcriptional regulators, MopA and MopB, with partially overlapping and specific functions in molybdate-dependent gene regulation. Both MopA and MopB consist of an N-terminal DNA-binding helix-turn-helix domain and a C-terminal molybdate-binding di-MOP domain. They formed homodimers as apo-proteins and in the molybdate-bound state as shown by yeast two-hybrid (Y2H) studies, glutaraldehyde cross-linking, gel filtration chromatography, and copurification experiments. Y2H studies suggested that both the DNA-binding and the molybdate-binding domains contribute to dimer formation. Analysis of molybdate binding to MopA and MopB revealed a binding stoichiometry of four molybdate oxyanions per homodimer. Specific interaction partners of MopA and MopB were the molybdate transporter ATPase ModC and the molbindin-like Mop protein, respectively. Like other molbindins, the R. capsulatus Mop protein formed hexamers, which were stabilized by binding of six molybdate oxyanions per hexamer. Heteromer formation of MopA and MopB was shown by Y2H studies and copurification experiments. Reporter gene activity of a strictly MopA-dependent mop-lacZ fusion in mutant strains defective for either mopA, mopB, or both suggested that MopB negatively modulates expression of the mop promoter. We propose that depletion of the active MopA homodimer pool by formation of MopA-MopB heteromers might represent a fine-tuning mechanism controlling mop gene expression.

* Corresponding author. Mailing address: Ruhr-Universität Bochum, Fakultät für Biologie und Biotechnologie, Lehrstuhl für Biologie der Mikroorganismen, 44780 Bochum, Germany. Phone: 49 (0) 234 32 25632. Fax: 49 (0) 234 32 14620. E-mail: bernd.masepohl{at}rub.de

{triangledown} Published ahead of print on 5 June 2009.

Journal of Bacteriology, August 2009, p. 5205-5215, Vol. 191, No. 16
0021-9193/09/$08.00+0     doi:10.1128/JB.00526-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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