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Journal of Bacteriology, August 2008, p. 5545-5554, Vol. 190, No. 16
0021-9193/08/$08.00+0     doi:10.1128/JB.01080-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Identification of Genes Involved in Inversion of Stereochemistry of a C-12 Hydroxyl Group in the Catabolism of Cholic Acid by Comamonas testosteroni TA441{triangledown}

Masae Horinouchi,1* Toshiaki Hayashi,1 Hiroyuki Koshino,1 Michal Malon,1 Takako Yamamoto,1 and Toshiaki Kudo1,2

RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan,1 Science of Biological Supermolecular Systems, Graduate School of Integrated Science, Yokohama City University, Suehiro, Tsurumi-ku, Yokohama 230-0045, Japan2

Received 8 July 2007/ Accepted 29 May 2008

Comamonas testosteroni TA441 degrades steroids such as testosterone via aromatization of the A ring, followed by meta-cleavage of the ring. In the DNA region upstream of the meta-cleavage enzyme gene tesB, two genes required during cholic acid degradation for the inversion of an {alpha}-oriented hydroxyl group on C-12 were identified. A dehydrogenase, SteA, converts 7{alpha},12{alpha}-dihydroxyandrosta-1,4-diene-3,17-dione to 7{alpha}-hydroxyandrosta-1,4-diene-3,12,17-trione, and a hydrogenase, SteB, converts the latter to 7{alpha},12β-dihydroxyandrosta-1,4-diene-3,17-dione. Both enzymes are members of the short-chain dehydrogenase/reductase superfamily. The transformation of 7{alpha},12{alpha}-dihydroxyandrosta-1,4-diene-3,17-dione to 7{alpha},12β-dihydroxyandrosta-1,4-diene-3,17-dione is carried out far more effectively when both SteA and SteB are involved together. These two enzymes are encoded by two adjacent genes and are presumed to be expressed together. Inversion of the hydroxyl group at C-12 is indispensable for the subsequent effective B-ring cleavage of the androstane compound. In addition to the compounds already mentioned, 12{alpha}-hydroxyandrosta-1,4,6-triene-3,17-dione and 12β-hydroxyandrosta-1,4,6-triene-3,17-dione were identified as minor intermediate compounds in cholic acid degradation by C. testosteroni TA441.

* Corresponding author. Mailing address: RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan. Phone: 81 48 467 9545. Fax: 81 48 462 4672. E-mail: masae{at}postman.riken.go.jp

{triangledown} Published ahead of print on 6 June 2008.

Journal of Bacteriology, August 2008, p. 5545-5554, Vol. 190, No. 16
0021-9193/08/$08.00+0     doi:10.1128/JB.01080-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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