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Journal of Bacteriology, September 2008, p. 6097-6110, Vol. 190, No. 18
0021-9193/08/$08.00+0     doi:10.1128/JB.00634-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

SoxAX Binding Protein, a Novel Component of the Thiosulfate-Oxidizing Multienzyme System in the Green Sulfur Bacterium Chlorobium tepidum{triangledown}

Takuro Ogawa,1,2 Toshinari Furusawa,1,2 Ryohei Nomura,2 Daisuke Seo,3 Naomi Hosoya-Matsuda,2 Hidehiro Sakurai,2,4 and Kazuhito Inoue2*

Graduate School of Science, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan,1 Department of Biological Sciences, Kanagawa University, Hiratsuka, Kanagawa 259-1293, Japan,2 Division of Material Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan,3 Department of Biology, School of Education, Wasea University, Nishiwaseda, Shinjuku, Tokyo 169-8050, Japan4

Received 7 May 2008/ Accepted 11 July 2008

From the photosynthetic green sulfur bacterium Chlorobium tepidum (pro synon. Chlorobaculum tepidum), we have purified three factors indispensable for the thiosulfate-dependent reduction of the small, monoheme cytochrome c554. These are homologues of sulfur-oxidizing (Sox) system factors found in various thiosulfate-oxidizing bacteria. The first factor is SoxYZ that serves as the acceptor for the reaction intermediates. The second factor is monomeric SoxB that is proposed to catalyze the hydrolytic cleavage of sulfate from the SoxYZ-bound oxidized product of thiosulfate. The third factor is the trimeric cytochrome c551, composed of the monoheme cytochrome SoxA, the monoheme cytochrome SoxX, and the product of the hypothetical open reading frame CT1020. The last three components were expressed separately in Escherichia coli cells and purified to homogeneity. In the presence of the other two Sox factors, the recombinant SoxA and SoxX showed a low but discernible thiosulfate-dependent cytochrome c554 reduction activity. The further addition of the recombinant CT1020 protein greatly increased the activity, and the total activity was as high as that of the native SoxAX-CT1020 protein complex. The recombinant CT1020 protein participated in the formation of a tight complex with SoxA and SoxX and will be referred to as SAXB (SoxAX binding protein). Homologues of the SAXB gene are found in many strains, comprising roughly about one-third of the thiosulfate-oxidizing bacteria whose sox gene cluster sequences have been deposited so far and ranging over the Chlorobiaciae, Chromatiaceae, Hydrogenophilaceae, Oceanospirillaceae, etc. Each of the deduced SoxA and SoxX proteins of these bacteria constitute groups that are distinct from those found in bacteria that apparently lack SAXB gene homologues.

* Corresponding author. Mailing address: Department of Biological Sciences, 15 Kanagawa University, Hiratsuka, Kanagawa 259-1293, Japan. Phone: 81 463-59-4111. Fax: 81 463-58-9684. E-mail: inoue-bio{at}kanagawa-u.ac.jp

{triangledown} Published ahead of print on 18 July 2008.

Journal of Bacteriology, September 2008, p. 6097-6110, Vol. 190, No. 18
0021-9193/08/$08.00+0     doi:10.1128/JB.00634-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Sauve, V., Roversi, P., Leath, K. J., Garman, E. F., Antrobus, R., Lea, S. M., Berks, B. C. (2009). Mechanism for the Hydrolysis of a Sulfur-Sulfur Bond Based on the Crystal Structure of the Thiosulfohydrolase SoxB. J. Biol. Chem. 284: 21707-21718 [Abstract] [Full Text]  


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