A Novel GH Family 20 β-N-acetylhexosaminidase With Both Chitosanase and Chitinase Activity From Aspergillus oryzae

Combinatorial metabolic engineering of Escherichia coli for de novo production of structurally defined and homogeneous Amino oligosaccharides

Amino oligosaccharides (AOs) possess various biological activities and are valuable in the pharmaceutical, food industries, and agriculture. However, the industrial manufacturing of AOs has not been realized yet, despite reports on physical, chemical, and biological approaches. In this study, the de novo production of chitin oligosaccharides (CHOS), a type of structurally defined AOs, was achieved in Escherichia coli through combinatorial pathway engineering. The most suitable glycosyltransferase for CHOS production was found to be NodCL from Mesorhizobium Loti. Then, by knocking out the nagB gene to block the flow of N-acetyl-d-glucosamine (NAG) to the glycolytic pathway in E. coli and adjusting the copy number of NodCL-coding gene, the CHOS yield was increased by 6.56 times. Subsequently, by introducing of UDP-N-acetylglucosamine (UDP-GlcNAc) salvage pathway for and optimizing fermentation conditions, the yield of CHOS reached 207.1 and 468.6 mg/L in shake-flask cultivation and a 5-L fed-batch bioreactor, respectively. Meanwhile, the concentration of UDP-GlcNAc was 91.0 mg/L, the highest level reported in E. coli so far. This study demonstrated, for the first time, the production of CHOS with distinct structures in plasmid-free E. coli, laying the groundwork for the biosynthesis of CHOS and providing a starting point for further engineering and commercial production.

A fungal pathogen secretes a cell wall-associated β-N-acetylhexosaminidase that is co-expressed with chitinases to contribute to infection of insects

BACKGROUND

β-N-acetylhexosaminidases (HEXs) are widely distributed in fungi and involved in cell wall chitin metabolism and utilization of chitin-containing substrates. However, details of the fungal pathogens-derived HEXs in the interaction with their hosts remain limited.

RESULTS

An insect nutrients-induced β-N-acetylhexosaminidase, BbHex1, was identified from the entomopathogenic fungus Beauveria bassiana, which was involved in cell wall modification and degradation of insect cuticle. BbHex1 was localized to cell wall and secreted, and displayed enzyme activity to degrade the chitinase-hydrolyzed product (GlcNAc)2. Disruption of BbHex1 resulted in a significant decrease in the level of cell wall chitin in the presence of insect nutrients and during infection of insects, with impaired ability to penetrate insect cuticle, accompanying downregulated cell wall metabolism-involved and cuticle-degrading chitinase genes. However, the opposite phenotypes were examined in the gene overexpression strain. Distinctly altered cell wall structures caused by BbHex1 mutation and overexpression led to the easy activation and evasion (respectively) of insect immune response during fungal infection. As a result, BbHex1 contributed to fungal virulence. Bioinformatics analysis revealed that promoters of some co-expressed chitinase genes with the BbHex1 promoter shared conserved transcription factors Skn7, Msn2 and Ste12, and CreA-binding motifs, implying co-regulation of those genes with BbHex1.

CONCLUSION

These data support a mechanism that the fungal pathogen specifically expresses BbHex1, which is co-expressed with chitinases to modify cell wall for evasion of insect immune recognition and to degrade insect cuticle, and contributes to the fungal virulence against insects. © 2024 Society of Chemical Industry.

Bioconversion of chitin into chitin oligosaccharides using a novel chitinase with high chitin-binding capacity

Chitin is the second largest renewable biomass resource in nature, it can be enzymatically degraded into high-value chitin oligosaccharides (CHOSs) by chitinases. In this study, a chitinase (ChiC8-1) was purified and biochemically characterized, its structure was analyzed by molecular modeling. ChiC8-1 had a molecular mass of approximately 96 kDa, exhibited its optimal activity at pH 6.0 and 50 °C. The K_m and V_max values of ChiC8-1 towards colloidal chitin were 10.17 mg mL^-1 and 13.32 U/mg, respectively. Notably, ChiC8-1 showed high chitin-binding capacity, which may be related to the two chitin binding domains in the N-terminal. Based on the unique properties of ChiC8-1, a modified affinity chromatography method, which combines protein purification with chitin hydrolysis process, was developed to purify ChiC8-1 while hydrolyzing chitin. In this way, 9.36 ± 0.18 g CHOSs powder was directly obtained by hydrolyzing 10 g colloidal chitin with crude enzyme solution. The CHOSs were composed of 14.77-2.83 % GlcNAc and 85.23-97.17 % (GlcNAc)₂ at different enzyme-substrate ratio. This process simplifies the tedious purification and separation steps, and may enable its potential application in the field of green production of chitin oligosaccharides.

Crude Enzyme Concentrate of Filamentous Fungus Hydrolyzed Chitosan to Obtain Oligomers of Different Sizes

Chitosan is a non-cytotoxic polysaccharide that, upon hydrolysis, releases oligomers of different sizes that may have antioxidant, antimicrobial activity and the inhibition of cancer cell growth, among other applications. It is, therefore, a hydrolysis process with great biotechnological relevance. Thus, this study aims to use a crude enzyme concentrate (C_EC) produced by a filamentous fungus to obtain oligomers with different molecular weights. The microorganism was cultivated in a liquid medium (modified Czapeck-with carboxymethylcellulose as enzyme inducer). The enzymes present in the C_EC were identified by LC-MS/MS, with an emphasis on cellobiohydrolase (E.C 3.2.1.91). The fungus of the Aspergillus genus was identified by amplifying the ITS1-5.8S-ITS2 rDNA region and metaproteomic analysis, where the excreted enzymes were identified with sequence coverage greater than 84% to A. nidulans. Chitosan hydrolysis assays compared the C_EC with the commercial enzyme (Celluclast 1.5 L^®). The ability to reduce the initial molecular mass of chitosan by 47.80, 75.24, and 93.26% after 2.0, 5.0, and 24 h of reaction, respectively, was observed. FTIR analyses revealed lower absorbance of chitosan oligomers' spectral signals, and their crystallinity was reduced after 3 h of hydrolysis. Based on these results, we can conclude that the crude enzyme concentrate showed a significant technological potential for obtaining chitosan oligomers of different sizes.

The Discovery, Enzymatic Characterization and Functional Analysis of a Newly Isolated Chitinase from Marine-Derived Fungus Aspergillus fumigatus df347

In order to discover a broad-specificity and high stability chitinase, a marine fungus, Aspergillus fumigatus df347, was identified in the sediments of mangrove wetlands in Qinzhou Bay, China. The chitinase gene (AfChi28) from A. fumigatus df347 was cloned and heterologously expressed in Escherichia coli, and the recombinant enzyme AfChi28 was purified and characterized. AfChi28 is an acido-halotolerant- and temperature-resistant bifunctional enzyme with both endo- and exo-cleavage functions. Its enzymatic products are mainly GlcNAc, (GlcNAc)2, (GlcNAc)3 and (GlcNAc)4. Na+, Mg2+, K+, Ca2+ and Tris at a concentration of 50 mM had a strong stimulatory effect on AfChi28. The crude enzyme and pure enzyme exhibited the highest specific activity of 0.737 mU/mg and 52.414 mU/mg towards colloidal chitin. The DxDxE motif at the end of strand β5 and with Glu154 as the catalytic residue was verified by the AlphaFold2 prediction and sequence alignment of homologous proteins. Moreover, the results of molecular docking showed that molecular modeling of chitohexaose was shown to bind to AfChi28 in subsites −4 to +2 in the deep groove substrate-binding pocket. This study demonstrates that AfChi28 is a promising chitinase for the preparation of desirable chitin oligosaccharides, and provides a foundation for elucidating the catalytic mechanism of chitinases from marine fungi.

Structural inspection and protein motions modelling of a fungal glycoside hydrolase family 18 chitinase by crystallography depicts a dynamic enzymatic mechanism

Chitinases degrade chitin into low molecular weight chitooligomers, which have a broad range of industrial, agricultural, and medical functions. Understanding the relationship between the diverse characteristics of chitinases and their functions is necessary for the improvement of functional enzymes that meet specific requirements. We report here a full crystallographic analysis of three complexes obtained from the chitinase Chit42 from Trichoderma harzianum, which represent different states along the enzymatic mechanism. The inactive double mutant D169A/E171A was submitted to soaking/crystallization experiments with hexa-N-acetyl-glucosamine (NAG6) or tetra-N-acetyl-glucosamine (NAG4), trapping the enzyme-substrate complex (Chit42-NAG6), the enzyme-products complex (Chit42-NAG4-NAG2) and a someway intermediate state. Structural comparison among the different complexes depicts the determinants defining the different subsites and revealed a previously unobserved dynamic on-off ligand binding process associated with a motion of its insertion domain, which might be accompanying the role or aromatics in processivity. An ensemble refinement performed to extract dynamic details from the diffraction data elucidates the implication of some highly flexible residues in the productive sliding of the substrate and the product release event. These positions were submitted to mutagenesis and the activity of the variants was investigated in the hydrolysis of NAG6, colloidal chitin and two chitosans with different polymerization and acetylation degree. All the changes affected the Chit42 hydrolytic activity therefore confirming the involvement of these positions in catalysis. Furthermore, we found the variants R295S and E316S improving the apparent catalytic efficiency of chitin and NAG6 and, together with E316A, enhancing the specific activity on chitosan. Therefore, our results provide novel insight into the molecular mechanisms underlying the hydrolysis of chitinous material by fungal chitinases, and suggest new targets to address engineering of these biotechnologically important enzymes.