Highly thermostable GH51 α-arabinofuranosidase from Hungateiclostridium clariflavum DSM 19732.

Arabinofuranosidase plays an essential role in the process of hydrolysis of arabinoxylan (AX). Thermostable, versatile, and efficient arabinofuranosidase is thus of great interest for the biorefinery industry. A GH51 arabinofuranosidase, Abf51, from Hungateiclostridium clariflavum DSM 19732 was heterogeneously expressed in Escherichia coli. Abf51 was found to have an optimal pH and temperature of 6.5 and 60 °C, respectively, with very high thermostability. At the optimal working temperature (60 °C), Abf51 retained over 90% activity after a 2-day incubation and over 60% activity after a 6-day incubation. Abf51 could effectively remove the arabinofuranosyls from three kinds of AX oligosaccharides [23-α-L-arabinofuranosyl-xylotriose (A2XX), 32-α-L-arabinofuranosyl-xylobiose (A3X), and 2333-di-α-L-arabinofuranosyl-xylotriose (A2 + 3XX)], which characterized as either single substitution or double substitution by arabinofuranosyls on terminal xylopyranosyl units. The maximal catalytic efficiency (Kcat/Km) was observed using p-nitrophenyl-α-L-arabinofuranoside (pNPAF) as a substrate (205.0 s-1 mM-1), followed by using A3X (22.8 s-1 mM-1), A2XX (6.9 s-1 mM-1), and A2 + 3XX (0.5 s-1 mM-1) as substrates. Moreover, the presence of Abf51 significantly stimulated the saccharification level of AX (18.5 g L-1) up to six times along with a β-xylanase as well as a β-xylosidase. Interestingly, in our survey of top thermostable arabinofuranosidases, most members were found from GH51, probably due to their owning of (β/α)8-barrel architectures. Our results suggested the great importance of GH51s as candidates for thermostable, versatile, and efficient arabinofuranosidases toward industry application.