Hydrolysis of ferulic acids in corn fiber by a metagenomic feruloyl esterase

Abstract

A feruloyl esterase (FAE) gene was isolated from rumen microbial metagenome that consisted of 774 bp encoding 258 amino acid residues. The gene was subcloned into pET 32b vector, expressed in Escherichia. coli, and the enzyme was purified in active form. Homology modeling showed that the FAE contained the catalytic triad composed of Ser80-His236-Asp177, and a classical Gly-X-Ser-X-Gly nucleophile motif commonly found in esterases. Under optimum pH and temperature (pH 7.0, 40 °C), 1 nmole FAE catalyzed the release of 19.75 ± 0.24 µg ferulic acid (FA) from 100 mg corn fiber (CF) in 1 h, which represents 3.5% of FA present in saponified CF. Addition of GH10 endoxylanase (XYN) to 0.5 nmole FAE enhanced the yield by 1.1 fold, equivalent to a 5% increase in FA release. Using CF pretreated with hot water, the synergistic effect of adding XYN resulted in 59.0 ± 0.2 mg FA/100 mg CF (5 nmole XYN, 0.5 nmole FAE), equivalent to a 4-fold increase compared to using the untreated CF substrate under the same reaction conditions.