*Article* **L-Fucose Synthesis Using a Halo- and Thermophilic L-Fucose Isomerase from Polyextremophilic** *Halothermothrix orenii*

**In Jung Kim <sup>1</sup> and Kyoung Heon Kim 1,2,\***


**Abstract:** L-Fucose isomerase (L-FucI)-mediated isomerization is a promising biotechnological approach for synthesizing various rare sugars of industrial significance, including L-fucose. Extremozymes that can retain their functional conformation under extreme conditions, such as high temperature and salinity, offer favorable applications in bioprocesses that accompany harsh conditions. To date, only one thermophilic L-FucI has been characterized for L-fucose synthesis. Here, we report L-FucI from *Halothermothrix orenii* (*Ho*FucI) which exhibits both halophilic and thermophilic properties. When evaluated under various biochemical conditions, *Ho*FucI exhibited optimal activities at 50–60 ◦C and pH 7 with 0.5–1 M NaCl in the presence of 1 mM Mn2+ as a cofactor. The results obtained here show a unique feature of *Ho*FucI as a polyextremozyme, which facilitates the biotechnological production of L-fucose using this enzyme.

**Keywords:** L-fucose isomerase; L-fucose; L-fuculose; extremophile; halothermophilic bacteria; *Halothermothrix orenii*
