High-Level Production of Isoleucine and Fusel Alcohol by Expression of the Feedback Inhibition-Insensitive Threonine Deaminase in <i>Saccharomyces cerevisiae</i>
Shota Isogai, Akira Nishimura, Atsushi Kotaka, Naoyuki Murakami, Natsuki Hotta, Hiroki Ishida, Hiroshi Takagi
Abstract
Fruit-like flavors of isoleucine-derived volatile compounds, 2-methyl-1-butanol (2MB) and its acetate ester, contribute to a variety of the flavors and tastes of alcoholic beverages. Besides its value as aroma components in foods and cosmetics, 2MB has attracted significant attention as second-generation biofuels. Threonine deaminase (TD) catalyzes the first step in isoleucine biosynthesis and its activity is subject to feedback inhibition by isoleucine. Here, we isolated an isoleucine-accumulating sake yeast mutant and identified a mutant gene encoding a novel variant of TD. The variant TD exhibited much less sensitivity to isoleucine, leading to higher production of 2MB as well as isoleucine than the wild-type TD. Furthermore, sake brewed with a mutant yeast expressing the variant TD contained more 2MB and its acetate ester than that brewed with the parent strain. These findings will contribute to the development of superior industrial yeast strains for high-level production of isoleucine and its related fusel alcohols.