Type C feruloyl esterase from Aspergillus ochraceus: A butanol specific biocatalyst for the synthesis of hydroxycinnamates in a ternary solvent system

摘要

Background Aspergillus ochraceus was isolated from coffee pulp and selected as an interesting hydroxycinnamoyl esterase strain producer, using an activity microplate high-throughput screening method. In this work, we purified and characterized a new type C A. ochraceus feruloyl esterase (AocFaeC), which synthesized specifically butyl hydroxycinnamates in a ternary solvent system. Results AocFaeC was produced by solid state fermentation, reaching its maximal activity (1.1?U/g) after 48?h of culture. After purification, the monomeric protein (34?kDa) showed a specific activity of 57.9?U/mg towards methyl ferulate. AocFaeC biochemical characterization confirmed its identity as a type C feruloyl esterase and suggested the presence of a catalytic serine in the active site. Its maximum hydrolytic activity was achieved at 40°C and pH?6.5 and increased by 109 and 77% with Ca 2+ and Mg 2+ , but decreased by 90 and 45% with Hg 2+ and Cu 2+ , respectively. The initial butyl ferulate synthesis rate increased from 0.8 to 23.7?nmol/min after transesterification condition improvement, using an isooctane:butanol:water ternary solvent system, surprisingly the synthesis activity using other alcohols was negligible. At these conditions, the synthesis specific activities for butyl p -coumarate, sinapinate, ferulate, and caffeate were 87.3, 97.6, 168.2, and 234?U/μmol, respectively. Remarkably, AocFaeC showed 5 folds higher butyl caffeate synthesis rate compared to type B Aspergillus niger feruloyl esterase, a well-known enzyme for its elevated activity towards caffeic acid esters. Conclusions Type C feruloyl esterase from A. ochraceus is a butanol specific biocatalyst for the synthesis of hydroxycinnamates in a ternary solvent system. How to cite: Romero E, Grajales D, Armendáriz M, et al. Type C feruloyl esterase from Aspergillus ochraceus : A butanol specific biocatalyst for the synthesis of hydroxycinnamates in a ternary solvent system. Electron J Biotechnol 2018;35. https://doi.org/10.1016/j.ejbt.2018.06.004 .