Engineering Saccharomyces cerevisiae to produce feruloyl esterase for the release of ferulic acid from switchgrass

The Aspergillus niger feruloyl esterase gene (faeA) was cloned into Saccharomyces cerevisiae via a yeast expression vector, resulting in efficient expression and secretion of the enzyme in the medium with a yield of similar to 2 mg/l. The recombinant enzyme was purified to homogeneity by anion-exchange and hydrophobic interaction chromatography. The specific activity was determined to be 8,200 U/mu g (pH 6.5, 20 degrees C, 3.5 mM 4-nitrophenyl ferulate). The protein had a correct N-terminal sequence of ASTQGISEDLY, indicating that the signal peptide was properly processed. The FAE exhibited an optimum pH of 6-7 and operated optimally at 50 degrees C using ground switchgrass as the substrate. The yeast clone was demonstrated to catalyze the release of ferulic acid continuously from switchgrass in YNB medium at 30 degrees C. This work represents the first report on engineering yeast for the breakdown of ferulic acid crosslink to facilitate consolidated bioprocessing.