Substrate and positional specificity of feruloyl esterases for monoferuloylated and monoacetylated 4-nitrophenyl glycosides

4-Nitrophenyl glycosides of 2-, 3-, and 5-O-(E)-feruloyl- and 2- and 5-O-acetyl-α-l-arabinofuranosides and of 2-, 3-, and 4-O-(E)-feruloyl- and 2-, 3- and 4-O-acetyl-β-d-xylopyranosides, compounds mimicking natural substrates, were used to investigate substrate and positional specificity of type-A, -B, and -C feruloyl esterases. All the feruloyl esterases behave as true feruloyl esterases showing negligible activity on sugar acetates. Type-A enzymes, represented by AnFaeA from Aspergillus niger and FoFaeII from Fusarium oxysporum, are specialized for deferuloylation of primary hydroxyl groups, with a very strong preference for hydrolyzing 5-O-feruloyl-α-l-arabinofuranoside. On the contrary, type-B and -C feruloyl esterases, represented by FoFaeI from F. oxysporum and TsFaeC from Talaromyces stipitatus, acted on almost all ferulates with exception of 4- and 3-O-feruloyl-β-d-xylopyranoside. 5-O-Feruloyl-α-l-arabinofuranoside was the best substrate for both TsFaeC and FoFaeI, although catalytic efficiency of the latter enzyme toward 2-O-feruloyl-α-l-arabinofuranoside was comparable. In comparison with acetates, the corresponding ferulates served as poor substrates for the carbohydrate esterase family 1 feruloyl esterase from Aspergillus oryzae. The enzyme hydrolyzed all α-l-arabinofuranoside and β-d-xylopyranoside acetates. It behaved as a non-specific acetyl esterase rather than a feruloyl esterase, with a preference for 2-O-acetyl-β-d-xylopyranoside.