Biochemical characterization and substrate profiling of a reversible 2,3-dihydroxybenzoic acid decarboxylase for biocatalytic Kolbe-Schmitt reaction.

Reversible benzoic acid decarboxylases are versatile biocatalysts by taking advantage of both decarboxylation and carboxylation reactions, especially for the biocatalytic Kolbe-Schmitt reaction. In the course of developing a benzoic acid decarboxylase tool-box, a putative benzoic acid decarboxylase gene from Fusarium oxysporum was heterologously over-expressed in Escherichia coli, the recombinant protein was purified and characterized. The purified enzyme exhibited relatively high catalytic efficiencies for the decarboxylation of 2, 3-dihydroxybenzoic acid and carboxylation of catechol (k _cat /K _m  = 2.03 × 10 ² and 1.88 mM ^-1  min ^-1 , respectively), and thus characterized as 2, 3-dihydroxybenzoic acid decarboxylase (2, 3-DHBD_Fo). The enzyme also catalyzed the decarboxylation of various substituted salicylic acids with different groups at varied positions except 5-position and the carboxylation of phenol and the substituted phenols. In a preparative reaction, catechol was carboxylated into 2, 3-dihydroxybenoic acid with 95% conversion by adding dodecyldimethylbenzylammonium chloride into the reaction system, and the product was isolated in 72% yield. These results demonstrate that 2, 3-DHBD_Fo is a valuable addition to the benzoic acid decarboxylase tool-box with potential practical applications.
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