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Journal of Bacteriology, September 2006, p. 6498-6505, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00548-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Tungsten Transport Protein A (WtpA) in Pyrococcus furiosus: the First Member of a New Class of Tungstate and Molybdate Transporters

Loes E. Bevers,1 Peter-Leon Hagedoorn,1 Gerard C. Krijger,2 and Wilfred R. Hagen1*

Department of Biotechnology, Delft University of Technology, Delft, The Netherlands,1 Department of Radiation, Radionuclides and Reactors, Delft University of Technology, Delft, The Netherlands2

Received 18 April 2006/ Accepted 3 July 2006

A novel tungstate and molybdate binding protein has been discovered from the hyperthermophilic archaeon Pyrococcus furiosus. This tungstate transport protein A (WtpA) is part of a new ABC transporter system selective for tungstate and molybdate. WtpA has very low sequence similarity with the earlier-characterized transport proteins ModA for molybdate and TupA for tungstate. Its structural gene is present in the genome of numerous archaea and some bacteria. The identification of this new tungstate and molybdate binding protein clarifies the mechanism of tungstate and molybdate transport in organisms that lack the known uptake systems associated with the ModA and TupA proteins, like many archaea. The periplasmic protein of this ABC transporter, WtpA (PF0080), was cloned and expressed in Escherichia coli. Using isothermal titration calorimetry, WtpA was observed to bind tungstate (dissociation constant [KD] of 17 ± 7 pM) and molybdate (KD of 11 ± 5 nM) with a stoichiometry of 1.0 mol oxoanion per mole of protein. These low KD values indicate that WtpA has a higher affinity for tungstate than do ModA and TupA and an affinity for molybdate similar to that of ModA. A displacement titration of molybdate-saturated WtpA with tungstate showed that the tungstate effectively replaced the molybdate in the binding site of the protein.

* Corresponding author. Mailing address: Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands. Phone: 31 15 2785051. Fax: 31 15 2782355. E-mail: w.r.hagen{at}tnw.tudelft.nl.

Journal of Bacteriology, September 2006, p. 6498-6505, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00548-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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