Overexpression, purification and characterisation of homologous α - l -arabinofuranosidase and endo -1,4- β - d -glucanase in Aspergillus vadensis

The carbohydrate metabolism and expression of carbohydrate-active enzyme genes in Aspergillus luchuensis fermentation of tea leaves

Introduction

Carbohydrates, which make up 20 to 25% of tea beverages, are responsible for their flavor and bioactivity. Carbohydrates of pu-erh tea change during microbial fermentation and require further research. In this study, we examined the carbohydrate metabolism and expression of carbohydrate-active enzyme genes during the fermentation of tea leaves with Aspergillus luchuensis.

Methods

Widely targeted metabolomics analysis, high-performance anion-exchange chromatography measurements, and transcriptomics were used in this study.

Results

After fermentation, the levels of soluble sugar, hemicellulose, lignin, eight monosaccharides, and seven sugar alcohols increased. Meanwhile, the relative contents of polysaccharides, D-sorbitol, D-glucose, and cellulose decreased. High expression of 40 genes encoding 16 carbohydrate enzymes was observed during fermentation (FPKM>10). These genes encode L-iditol 2-dehydrogenase, pectinesterase, polygalacturonase, α-amylase, glucoamylase, endoglucanase, β-glucosidase, β-galactosidase, α-galactosidase, α-glucosidase, and glucose-6-phosphate isomerase, among others.

Discussion

These enzymes are known to break down polysaccharides and cell wall cellulose, increasing the content of monosaccharides and soluble sugars.

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.

Cloning and Characterization of an Endoglucanase Gene from Actinomyces sp. Korean Native Goat 40

A gene from Actinomyces sp. Korean native goat (KNG) 40 that encodes an endo-β-1,4-glucanase, EG1, was cloned and expressed in Escherichia coli (E. coli) DH5α. Recombinant plasmid DNA from a positive clone with a 3.2 kb insert hydrolyzing carboxyl methyl-cellulose (CMC) was designated as pDS3. The entire nucleotide sequence was determined, and an open-reading frame (ORF) was deduced. The ORF encodes a polypeptide of 684 amino acids. The recombinant EG1 produced in E. coli DH5α harboring pDS3 was purified in one step using affinity chromatography on crystalline cellulose and characterized. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis/zymogram analysis of the purified enzyme revealed two protein bands of 57.1 and 54.1 kDa. The amino terminal sequences of these two bands matched those of the deduced ones, starting from residue 166 and 208, respectively. Putative signal sequences, a Shine–Dalgarno-type ribosomal binding site, and promoter sequences related to the consensus sequences were deduced. EG1 has a typical tripartite structure of cellulase, a catalytic domain, a serine-rich linker region, and a cellulose-binding domain. The optimal temperature for the activity of the purified enzyme was 55°C, but it retained over 90% of maximum activity in a broad temperature range (40°C to 60°C). The optimal pH for the enzyme activity was 6.0. Kinetic parameters, K_m and V_max of rEG1 were 0.39% CMC and 143 U/mg, respectively.