Phenolic Acid Decarboxylase for Carbon Dioxide Fixation: Mining, Biochemical Characterization, and Regioselective Enzymatic β-carboxylation of para-hydroxystyrene Derivatives

The use of CO₂ as a C1 carbon source for the synthesis of valuable chemicals through biotechnology methods represents an effective strategy to fix carbon dioxide. Phenolic acid decarboxylases possess the capability to introduce a carboxyl group into para-hydroxystyrenes for the regionally selective synthesis of (E)-para-hydroxycinnamic acids, utilizing bicarbonate as a CO₂ source. It is difficult to achieve this reaction with traditional chemical methods, and only a few enzymes have been isolated and characterized. Here, we mined which low amino acid sequence shared its identity with those of related decarboxylases and which heterologously expressed phenolic acid decarboxylase PAD_Cs from Clostridium sp. DSM 8431 in E. coli. The recombinant PAD_Cs displayed maximum activity at 50 °C, and pH 5.0. PAD_Cs showed distinct carboxylation ability. The carboxylated substrates have a wide range of substitution modes on aromatic systems, including alkyl and alkoxy groups as well as halogens. Furthermore, the carboxylation conversion rates were impressive: para-hydroxystyrene exceeded 20% and 2-methoxy-4-vinylphenol surpassed 26%. This study indicated that PAD_Cs might serve as a potential enzyme source in biotechnological CO₂ fixation.