Diversity of fungal feruloyl esterases: updated phylogenetic classification, properties, and industrial applications

Abstract

Feruloyl esterases (FAEs) represent a diverse group of carboxyl esterases that specifically catalyze the hydrolysis of ester bonds between ferulic (hydroxycinnamic) acid and plant cell wall polysaccharides. Therefore, FAEs act as accessory enzymes to assist xylanolytic and pectinolytic enzymes in gaining access to their site of action during biomass conversion. Their ability to release ferulic acid and other hydroxycinnamic acids from plant biomass makes FAEs potential biocatalysts in a wide variety of applications such as in biofuel, food and feed, pulp and paper, cosmetics, and pharmaceutical industries. This review provides an updated overview of the knowledge on fungal FAEs, in particular describing their role in plant biomass degradation, diversity of their biochemical properties and substrate specificities, their regulation and conditions needed for their induction. Furthermore, the discovery of new FAEs using genome mining and phylogenetic analysis of current publicly accessible fungal genomes will also be presented. This has led to a new subfamily classification of fungal FAEs that takes into account both phylogeny and substrate specificity.

Keywords: Applications; Biotechnology; Cinnamic acid; Ferulic acid; Feruloyl esterase; Hydroxycinnamic acid; P-coumaric acid; Phylogenetic analysis; Plant cell wall.

Fig. 1

Model structures of hydroxycinnamic acids, feruloylated plant cell wall polysaccharides and the site of attack by the carbohydrate-active enzymes (modified from [8, 15]). a p-coumaric acid, b caffeic acid, c ferulic acid, d sinapic acid, e feruloylated glucuronoarabinoxylan, f feruloylated pectic rhamnogalacturonan I, g 8,5′-(benzofuran)-diferulic acid, h 8,5′-diferulic acid, i 5,5′-diferulic acid, j 8,4′-diferulic acid, k 8,8′-diferulic acid, l 8,8′-(aryl)-diferulic acid. ABF α-arabinofuranosidase; ABN endoarabinanase; ABX exoarabinanase; AXE acetyl xylan esterase; BXL β-1,4-xylosidase; FAE feruloyl esterase; GAL β-1,4-endogalactanase; GUS α-glucuronidase; LAC β-1,4-galactosidase; RGAE rhamnogalacturonan acetyl esterase; RGL rhamnogalacturonan lyase; RGX exorhamnogalacturonase; RHG endorhamnogalacturonase; XLN β-1,4-endoxylanase

Fig. 2

Phylogenetic relationships among the (putative) fungal FAEs. Glucuronoyl esterases (GEs, green-filled circles) were used as an outgroup. AXE, acetyl xylan esterase (blue-filled circles); LIP, lipase (yellow-filled squares); SF, subfamily; TAN, tannase (purple-filled circles). FAEs from previously reported phylogenetic analysis [51] were marked with magenta open triangles for SF1, magenta open rhombuses for SF2-4, magenta-filled triangles for SF5, magenta-filled rhombuses for SF6, light blue-filled squares for SF7, brown-filled circles for AtFAE2 and AtFAE3, and magenta-filled circles for ungrouped ones. Light blue-filled circles indicate ungrouped sequences which numbering indicates different groups

Fig. 3

Schematic overview of industrial applications of FAEs (modified from [51])

Fig. 4

Transferuloylation reaction (modified from [64])