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Tyrosinases (TYRs) catalyze two-step consecutive oxidation reactions of monophenolic compounds. Since known TYRs have optimal pH at neutral to somewhat basic pH, they have limitations to be used for production of catechol derivatives. In this study, we identified TYR from Burkholderia thailandensis (BtTYR), which exhibited high tyrosinase activity at low pH. We determined the crystal structure of BtTYR and provided the structural basis for the regulation of its activity in response to pH change. At high pH, BtTYR is inactivated due to the tight binding of its TYR and CAP domains, although it is stable in monomer form; at low pH, however, the protein is activated by the typical opening of the CAP domain, and the formation of tetramers maintains the stability of the protein. Such unique tyrosinase activity of BtTYR at acidic pH was successfully applied to highly efficient production of catechol derivatives and fabrication of an adhesive hydrogel.

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Soy isoflavones are naturally occurring phytochemicals, which are biotransformed into functional derivatives through oxidative and reductive metabolic pathways of diverse microorganisms. Such representative derivatives, ortho-dihydroxyisoflavones (ODIs) and equols, have attracted great attention for their versatile health benefits since they were found from soybean fermented foods and human intestinal fluids. Recently, scientists in food technology, nutrition and microbiology began to understand their correct biosynthetic pathways and nutraceutical values, and have attempted to produce the valuable bioactive compounds using microbial fermentation and whole-cell/enzyme-based biotransformation. Furthermore, artificial design of microbial catalysts and/or protein engineering of oxidoreductases were also conducted to enhance production efficiency and regioselectivity of products. This minireview summarizes and introduces the past year's studies and recent advances in notable production of ODIs and equols, and provides information on available microbial species and their catalytic performance with perspectives on industrial application.

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