Molecular Characterization of Reversible Decarboxylases Catalyzing CO_2 Fixation and Their Application to Molecular Conversion Process

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Generally, decarboxylases can not catalyze the reverse carboxylation reaction. However, we found novel decarboxylases efficiently catalyzing nonoxidative decarboxyation. In the metabolism of phenol in the absence of oxygen, 4-hydroxybenzoate decarboxylase found to catalyze carbon dioxide fixation. In the view point of application to chemical industry, the reversible decarboxylases are useful for the synthesis of aromatic carboxylic acids, because a carboxyl group is regioselectively introduced into aromatic ring. In the present research, we screened novel decarboxylases reversibly catalyzing nonoxidative decarboxylation, revealed physicochemical and molecular characteristics, and evaluated the reverse carboxylation activities.The primary structures of pyrrole-2-carboxylate decarboxylase and indole-3carboxylate decarboxylase were determined from their gene analysis. These decarboxylases showed similarity to various microbial hypothetical proteins. In the screening of 4-hydroxybenzoate decarboxylase, the enzyme activity was widely detected in various bacteria, actinomycetes and yeasts, contrary to the previous observation. As for 2,6-dihydroxybenzoate decarboxylase, a novel decarboxylase, the efficient regioselecetive carboxylation of 1,3-dihydroxybenzene was confirmed in the presence of KHCO_3. From the analyses for enzymatic properties and structures, various reversible decarboxylase were classified into two subgroups.