A Glycoside Hydrolase Family 62 A-L-Arabinofuranosidase from Trichoderma Reesei and Its Applicable Potential during Mashing

Microbial α-L-arabinofuranosidases: diversity, properties, and biotechnological applications

Arabinoxylans (AXs) are hemicellulosic polysaccharides consisting of a linear backbone of β-1,4-linked xylose residues branched by high content of α-L-arabinofuranosyl (Araf) residues along with other side-chain substituents, and are abundantly found in various agricultural crops especially cereals. The efficient bioconversion of AXs into monosaccharides, oligosaccharides and/or other chemicals depends on the synergism of main-chain enzymes and de-branching enzymes. Exo-α-L-arabinofuranosidases (ABFs) catalyze the hydrolysis of terminal non-reducing α-1,2-, α-1,3- or α-1,5- linked α-L-Araf residues from arabinose-substituted polysaccharides or oligosaccharides. ABFs are critically de-branching enzymes in bioconversion of agricultural biomass, and have received special attention due to their application potentials in biotechnological industries. In recent years, the researches on microbial ABFs have developed quickly in the aspects of the gene mining, properties of novel members, catalytic mechanisms, methodologies, and application technologies. In this review, we systematically summarize the latest advances in microbial ABFs, and discuss the future perspectives of the enzyme research.

Using One-pot Fermentation Technology to Prepare Enzyme Cocktail to Sustainably Produce Low Molecular Weight Galactomannans from Sesbania cannabina Seeds

Enzymatic hydrolysis using β-mannanase and α-galactosidase is necessary to produce low molecular weight galactomannan (LMW-GM) from galactomannans (GM) in the leguminous seeds. In this study, different ratios of avicel and melibiose were used as the inductors (carbon sources) for Trichoderma reesei to metabolize the enzyme cocktail containing β-mannanase and α-galactosidase using one-pot fermentation technology. The obtained enzyme cocktail was used to efficiently produce LMW-GM from GM in Sesbania cannabina seeds. Results showed that 15 g/L avicel and 10 g/L melibiose were the best carbon sources to prepare enzyme cocktail containing β-mannanase and α-galactosidase with activities of 3.69 ± 0.27 U/mL and 0.51 ± 0.02 U/mL, respectively. Specifically, melibiose could effectively induce the metabolite product of α-galactosidase by T. reesei, which showed good performance in degrading the galactose substituent from GM backbone. The degradation of galactose alleviated the spatial site-blocking effect for enzymatic hydrolysis by β-mannanase and improved the yield of LMW-GM. This research can lay the foundation for the industrial technology amplification of LMW-GM production for further application.

Overexpression of a wheat α-amylase type 2 impact on starch metabolism and abscisic acid sensitivity during grain germination

Despite being of vital importance for seed establishment and grain quality, starch degradation remains poorly understood in organs such as cereal or legume seeds. In cereals, starch degradation requires the synergetic action of different isoforms of α-amylases. Ubiquitous overexpression of TaAmy2 resulted in a 2.0-437.6-fold increase of total α-amylase activity in developing leaf and harvested grains. These increases led to dramatic alterations of starch visco-properties and augmentation of soluble carbohydrate levels (mainly sucrose and α-gluco-oligosaccharide) in grain. Interestingly, the overexpression of TaAMY2 led to an absence of dormancy in ripened grain due to abscisic acid (ABA) insensitivity. Using an allosteric α-amylase inhibitor (acarbose), we demonstrated that ABA insensitivity was due to the increased soluble carbohydrate generated by the α-amylase excess. Independent from the TaAMY2 overexpression, inhibition of α-amylase during germination led to the accumulation of soluble α-gluco-oligosaccharides without affecting the first stage of germination. These findings support the hypotheses that (i) endosperm sugar may overcome ABA signalling and promote sprouting, and (ii) α-amylase may not be required for the initial stage of grain germination, an observation that questions the function of the amylolytic enzyme in the starch degradation process during germination.