Cloning, Characterization, and Functional Expression of a Thermostable Type B Feruloyl Esterase from Thermophilic Thielavia Terrestris

Feruloyl esterases (FAEs) have great potential applications in paper and breeding industry. A new thermo-stable feruloyl esterase gene, TtfaeB was identified from the thermophilic fungus Thielavia terrestris h408. Deduced protein sequence shares the identity of 67% with FAEB from Neurospora crassa. The expression vector pPIC9K-TtfaeB was successfully constructed and electro-transformed into GS115 strain of Pichia pastoris. One transformant with high feruloyl esterase yield was obtained through plate screening and named TtFAEB1. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of fermentation supernatant from transformant TtFAEB1 showed a distinct protein band appearing at the position of about 35-kDa, indicating that TtfaeB gene has been successfully expressed in P. pastoris. The recombinant TtFAEB was purified by affinity chromatography and the specific activity of purified TtFAEB was 6.06 +/- 0.72 U/mg. The optimal temperature and pH for purified recombinant TtFAEB was 60 degrees C and 7.0, respectively. TtFAEB was thermostable, retaining 96.89 and 84.16% of the maximum activity after being treated for 1 h at 50 degrees C and 60 degrees C, respectively. Additionally, the enzyme was stable in the pH range 4.5-8.0. The homology model of TtFAEB showed that it consists of a single domain adopting a typical alpha/beta-hydrolase fold and contains a catalytic triad formed by Ser117, Asp201, and His260. TtFAEB in association with xylanase from Trichoderma reesei could release 77.1% of FA from destarched wheat bran. The present results indicated that the recombinant TtFAEB with excellent enzymatic properties is a promising candidate for potential applications in biomass deconstruction and biorefinery.