A novel l-isoleucine metabolism in Bacillus thuringiensis generating (2S,3R,4S)-4-hydroxyisoleucine, a potential insulinotropic and anti-obesity amino acid
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4-Hydroxyisoleucine (HIL) found in fenugreek seeds has insulinotropic and anti-obesity effects and is expected to be a novel orally active drug for insulin-independent diabetes. Here, we show that the newly isolated strain Bacillus thuringiensis 2e2 and the closely related strain B. thuringiensis ATCC 35646 operate a novel metabolic pathway for l-isoleucine (l-Ile) via HIL and 2-amino-3-methyl-4-ketopentanoic acid (AMKP). The HIL synthesis was catalyzed stereoselectively by an α-ketoglutaric acid-dependent dioxygenase and to be useful for efficient production of a naturally occurring HIL isomer, (2S,3R,4S)-HIL. The (2S,3R,4S)-HIL was oxidized to (2S,3R)-AMKP by a NAD+-dependent dehydrogenase. The metabolic pathway functions as an effective bypass pathway that compensates for the incomplete tricarboxylic acid (TCA) cycle in Bacillus species and also explains how AMKP, a vitamin B12 antimetabolite with antibiotic activity, is synthesized. These novel findings pave a new way for the commercial production of HIL and also for AMKP.
Keywordsl-Isoleucine dioxygenase 4-Hydroxyisoleucine NAD+-dependent dehydrogenase 2-Amino-3-methyl-4-ketopentanoic acid Bacillus thuringiensis TCA cycle
This work was partially supported by the Project for Development of a Technological Infrastructure for Industrial Bioprocesses on R&D of New Industrial Science and Technology Frontiers (to S. Shimizu and J. Ogawa) from the New Energy and Industrial Technology Development Organization (NEDO) of Japan, Grants-in-Aid for Scientific Research (no. 21780070 to M. Hibi), and COE for Microbial-Process Development Pioneering Future Production Systems (to S. Shimizu) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Res. Div. Microb. Sci. (J. Ogawa) is an endowed laboratory of the Institute for Fermentation, Osaka (IFO).
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