Abstract
Ferulic acid (FA), a component of hemicellulose in plant cell walls, is a phenolic acid with several potential applications based on its antioxidant properties. Recent studies have shown that feruloyl esterase (FAE) is a key bacterial enzyme involved in FA production from agricultural biomass. In this study, we screened a library of 43 esterases from Streptomyces species and identified two enzymes, R18 and R43, that have FAE activity toward ethyl ferulate. In addition, we characterized their enzyme properties in detail. R18 and R43 showed esterase activity toward other hydroxycinnamic acid esters as well, such as methyl p-coumarate, methyl caffeate, and methyl sinapinate. The amino acid sequences of R18 and R43 were neither similar to each other, nor to other FAEs. We found that R18 and R43 individually showed the ability to produce FA from corn bran; however, combination with other Streptomyces enzymes, namely xylanase and α-l-arabinofuranosidase, increased FA production from biomass such as corn bran, defatted rice bran, and wheat bran. These results suggest that R18 and R43 are effective FAEs for the enzymatic production of FA from biomass.
Highlights
Ferulic acid (4-hydroxy-3-methoxycinnamic acid, FA) is a phenolic acid that is found abundantly in the hemicellulose of plant cell walls, where it cross-links arabinoxylan molecules via arabinose residues, in addition to others, within the Poaceae plant family
We screened for enzymes showing feruloyl esterase (FAE) activity, using ethyl ferulate as substrate
The sequences of R18 and R43 were not assigned to the FAE class of proteins based on their amino acid sequences because they did not share sequence similarity with known FAEs
Summary
Ferulic acid (4-hydroxy-3-methoxycinnamic acid, FA) is a phenolic acid that is found abundantly in the hemicellulose of plant cell walls, where it cross-links arabinoxylan molecules via arabinose residues, in addition to others, within the Poaceae plant family. Enzymatic production of FA from biomass has been reported previously [7,8], and feruloyl esterase (FAE) has been identified as a key enzyme in the process [9]. Streptomyces is a widely used bacterium and the genomic sequences of several Streptomyces species have been identified [16,17]. We found two new esterases (i.e., R18 and R43) that had feruloyl esterase activity toward ethyl ferulate. We characterized these enzymes with respect to optimal pH, optimal temperature, and thermal stabilization. We investigated their substrate specificities using ethyl ferulate and methyl-esters of other hydroxycinnamic acids as substrates. We investigated FA production by R18 and R43 from agricultural biomass such as corn bran, defatted rice bran, and wheat bran
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