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Journal of Bacteriology, June 2005, p. 3636-3642, Vol. 187, No. 11
0021-9193/05/$08.00+0     doi:10.1128/JB.187.11.3636-3642.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

The Archaeon Pyrococcus horikoshii Possesses a Bifunctional Enzyme for Formaldehyde Fixation via the Ribulose Monophosphate Pathway

Izumi Orita,1 Hiroya Yurimoto,1* Reiko Hirai,1 Yutaka Kawarabayasi,2 Yasuyoshi Sakai,1 and Nobuo Kato1

Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502,1 Research Center for Glycoscience, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8561, Japan2

Received 22 December 2004/ Accepted 1 March 2005

Pyrococcus horikoshii OT3, a hyperthermophilic and anaerobic archaeon, was found to have an open reading frame (PH1938) whose deduced amino acid sequence of the N-terminal and C-terminal halves showed significant similarity to two key enzymes of the ribulose monophosphate pathway for formaldehyde fixation in methylotrophic bacteria, 3-hexulose-6-phosphate synthase (HPS) and 6-phospho-3-hexuloisomerase (PHI), respectively. The organism constitutively produced the encoded protein and exhibited activity of the sequential HPS- and PHI-mediated reactions in a particulate fraction. The full-length gene encoding the hybrid enzyme, the sequence corresponding to the HPS region, and the sequence corresponding to the PHI region were expressed in Escherichia coli and were found to produce active enzymes, rHps-Phi, rHps, or rPhi, respectively. Purified rHps-Phi and rHps were found to be active at the growth temperatures of the parent strain, but purified rPhi exhibited significant susceptibility to heat, suggesting that thermostability of the PHI moiety of the bifunctional enzyme (rHps-Phi) resulted from fusion with HPS. The bifunctional enzyme catalyzed the sequential reaction much more efficiently than a mixture of rHps and rPhi. These and other biochemical characterizations of the PH1938 gene product suggest that the ribulose monophosphate pathway plays a significant role in the archaeon under extreme environmental conditions.

* Corresponding author. Mailing address: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Sakyo-ku, Kyoto 606-8502, Japan. Phone: 81-75-753-6387. Fax: 81-75-753-6385. E-mail: yury{at}kais.kyoto-u.ac.jp.

Journal of Bacteriology, June 2005, p. 3636-3642, Vol. 187, No. 11
0021-9193/05/$08.00+0     doi:10.1128/JB.187.11.3636-3642.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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