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J Bacteriol, May 1998, p. 2583-2589, Vol. 180, No. 10
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Cloning of Genes Coding for the Three Subunits of Thiocyanate Hydrolase of Thiobacillus thioparus THI 115 and Their Evolutionary Relationships to Nitrile Hydratase

Yoko Katayama,1,* Yasuhiko Matsushita,2 Miyuki Kaneko,1 Mai Kondo,2,dagger Tadayoshi Mizuno,1,Dagger and Hiroshi Nyunoya2

Faculty of Agriculture,1 and Gene Research Center,2 Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183, Japan

Received 20 October 1997/Accepted 19 March 1998

Thiocyanate hydrolase is a newly found enzyme from Thiobacillus thioparus THI 115 that converts thiocyanate to carbonyl sulfide and ammonia (Y. Katayama, Y. Narahara, Y. Inoue, F. Amano, T. Kanagawa, and H. Kuraishi, J. Biol. Chem. 267:9170-9175, 1992). We have cloned and sequenced the scn genes that encode the three subunits of the enzyme. The scnB, scnA, and scnC genes, arrayed in this order, contained open reading frames encoding sequences of 157, 126, and 243 amino acid residues, respectively, for the beta , alpha , and gamma  subunits, respectively. Each open reading frame was preceded by a typical Shine-Dalgarno sequence. The deduced amino-terminal peptide sequences for the three subunits were in fair agreement with the chemically determined sequences. The protein molecular mass calculated for each subunit was compatible with that determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. From a computer analysis, thiocyanate hydrolase showed significant homologies to bacterial nitrile hydratases known to convert nitrile to the corresponding amide, which is further hydrolyzed by amidase to form acid and ammonia. The two enzymes were homologous over regions corresponding to almost the entire coding regions of the genes: the beta  and alpha  subunits of thiocyanate hydrolase were homologous to the amino- and carboxyl-terminal halves of the beta  subunit of nitrile hydratase, and the gamma  subunit of thiocyanate hydrolase was homologous to the alpha  subunit of nitrile hydratase. Comparisons of the catalytic properties of the two homologous enzymes support the model for the reaction steps of thiocyanate hydrolase that was previously presented on the basis of biochemical analyses.

* Corresponding author. Mailing address: Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183, Japan. Phone: 81-42-367-5732. Fax: 81-42-360-8830. E-mail: katayama{at}cc.tuat.ac.jp.

dagger Present address: Human Genome Center, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108, Japan.

Dagger Present address: Tsukuba Research Laboratories, Sankyo Co. Ltd., 33, Miyukigaoka, Tsukuba-shi, Ibaraki 305, Japan.

J Bacteriol, May 1998, p. 2583-2589, Vol. 180, No. 10
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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