Active-site mutations improved the transglycosylation activity of Stenotrophomonas maltophilia chitinase A

Green-Chemical Strategies for Production of Tailor-Made Chitooligosaccharides with Enhanced Biological Activities

Chitooligosaccharides (COSs) are b-1,4-linked homo-oligosaccharides of N-acetylglucosamine (GlcNAc) or glucosamine (GlcN), and also include hetero-oligosaccharides composed of GlcNAc and GlcN. These sugars are of practical importance because of their various biological activities, such as antimicrobial, anti-inflammatory, antioxidant and antitumor activities, as well as triggering the innate immunity in plants. The reported data on bioactivities of COSs used to contain some uncertainties or contradictions, because the experiments were conducted with poorly characterized COS mixtures. Recently, COSs have been satisfactorily characterized with respect to their structures, especially the degree of polymerization (DP) and degree of N-acetylation (DA); thus, the structure-bioactivity relationship of COSs has become more unambiguous. To date, various green-chemical strategies involving enzymatic synthesis of COSs with designed sequences and desired biological activities have been developed. The enzymatic strategies could involve transglycosylation or glycosynthase reactions using reducing end-activated sugars as the donor substrates and chitinase/chitosanase and their mutants as the biocatalysts. Site-specific chitin deacetylases were also proposed to be applicable for this purpose. Furthermore, to improve the yields of the COS products, metabolic engineering techniques could be applied. The above-mentioned approaches will provide the opportunity to produce tailor-made COSs, leading to the enhanced utilization of chitin biomass.

N-acetyl-d-glucosamine-based oligosaccharides from chitin: Enzymatic production, characterization and biological activities

Chitin, the second most abundant biopolymer, possesses diverse applications in the food, agricultural, and pharmaceutical industries due to its functional properties. However, the potential applications of chitin are limited owing to its high crystallinity and low solubility. N-acetyl chitooligosaccharides and lacto-N-triose II, the two types of GlcNAc-based oligosaccharides, can be obtained from chitin by enzymatic methods. With their lower molecular weights and improved solubility, these two types of GlcNAc-based oligosaccharides display more various beneficial health effects when compared to chitin. Among their abilities, they have exhibited antioxidant, anti-inflammatory, anti-tumor, antimicrobial, and plant elicitor activities as well as immunomodulatory and prebiotic effects, which suggests they have the potential to be utilized as food additives, functional daily supplements, drug precursors, elicitors for plants, and prebiotics. This review comprehensively covers the enzymatic methods used for the two types of GlcNAc-based oligosaccharides production from chitin by chitinolytic enzymes. Moreover, current advances in the structural characterization and biological activities of these two types of GlcNAc-based oligosaccharides are summarized in the review. We also highlight current problems in the production of these oligosaccharides and trends in their development, aiming to offer some directions for producing functional oligosaccharides from chitin.

Purification and characterization of a chitinase from Aeromonas media CZW001 as a biocatalyst for producing chitinpentaose and chitinhexaose

Developing chitinase suitable for the bioconversion of chitin to chitin oligosaccharides has attracted significant attention due to its benefits in environmental protection. In this study, chitinase from Aeromonas media CZW001 (AmChi) was purified and characterized. The molecular weight of AmChi was approximately 40 kDa. AmChi exhibited maximum catalytic activity at pH 8.0 with an optimum temperature of 55°C and showed broad stability between 15 and 65°C and between pH 5.0 and 9.0. AmChi was activated by Mg²⁺ , Na⁺ , and K⁺ and inhibited by Hg⁺ , Co²⁺ , Fe²⁺ , Ca²⁺ , Ag⁺ , Zn²⁺ , and EDTA. The main products of AmChi on colloidal chitin were chitinhexaose and chitinpentaose. AmChi had better substrate specificity for powdered chitin than colloidal chitin and had a higher catalytic efficiency toward (GlcNAc)₅ than colloidal chitin. AmChi inhibited fungal growth in a dose-dependent manner. These results suggest that AmChi could be used for the enzymatic degradation of chitin to produce chitinhexaose and chitinpentaose, which have several industrial applications.

The role of oviduct-specific glycoprotein (OVGP1) in modulating biological functions of gametes and embryos

Diverse lines of evidence indicate that the mammalian oviduct makes important contributions to the complex process of reproduction other than being simply a conduit for the transport of gametes and embryos. The cumulative synthesis and transport of proteins secreted by oviductal secretory cells into the oviductal lumen create a microenvironment supporting important reproductive events, including sperm capacitation, fertilization, and early embryo development. Among the components that have been identified in the oviductal fluid is a family of glycosylated proteins known collectively as oviduct-specific glycoprotein (OVGP1) or oviductin. OVGP1 has been identified in several mammalian species, including humans. The present review summarizes the work carried out, in various mammalian species, by many research groups revealing the synthesis and secretion of OVGP1, its fate in the female reproductive tract upon secretion by the oviductal epithelium, and its role in modulating biological functions of gametes and embryos. The production and functions of recombinant human OVGP1 and recombinant OVGP1 of other mammalian species are also discussed. Some of the findings obtained with immunocytochemistry will be highlighted in the present review. It is hoped that the findings obtained from recent studies carried out with recombinant OVGP1 from various species will rekindle researchers’ interest in pursuing further the role of the oviductal microenvironment, of which OVGP1 is a major component, in contributing to the successful occurrence of early reproductive events, and the potential use of OVGP1 in improving the current assisted reproductive technology in alleviating infertility.

Reprint of: Advanced glycosidases as ingenious biosynthetic instruments

Until recently, glycosidases, naturally hydrolyzing carbohydrate-active enzymes, have found few synthetic applications in industry, being primarily used for cleaving unwanted carbohydrates. With the establishment of glycosynthase and transglycosidase technology by genetic engineering, the view of glycosidases as industrial biotechnology tools has started to change. Their easy production, affordability, robustness, and substrate versatility, added to the possibility of controlling undesired side hydrolysis by enzyme engineering, have made glycosidases competitive synthetic tools. Current promising applications of engineered glycosidases include the production of well-defined chitooligomers, precious galactooligosaccharides or specialty chemicals such as glycosylated flavonoids. Other synthetic pathways leading to human milk oligosaccharides or remodeled antibodies are on the horizon. This work provides an overview of the synthetic achievements to date for glycosidases, emphasizing the latest trends and outlining possible developments in the field.

Advanced glycosidases as ingenious biosynthetic instruments

Until recently, glycosidases, naturally hydrolyzing carbohydrate-active enzymes, have found few synthetic applications in industry, being primarily used for cleaving unwanted carbohydrates. With the establishment of glycosynthase and transglycosidase technology by genetic engineering, the view of glycosidases as industrial biotechnology tools has started to change. Their easy production, affordability, robustness, and substrate versatility, added to the possibility of controlling undesired side hydrolysis by enzyme engineering, have made glycosidases competitive synthetic tools. Current promising applications of engineered glycosidases include the production of well-defined chitooligomers, precious galactooligosaccharides or specialty chemicals such as glycosylated flavonoids. Other synthetic pathways leading to human milk oligosaccharides or remodeled antibodies are on the horizon. This work provides an overview of the synthetic achievements to date for glycosidases, emphasizing the latest trends and outlining possible developments in the field.

New Class of Chitosanase from Bacillus amyloliquefaciens for the Generation of Chitooligosaccharides

Chitooligosaccharides (COS) generated from either chitin (chitin oligosaccharides) or chitosan (chitosan oligosaccharides) have a wide range of applications in agriculture, medicine, and other fields. Here, we report the characterization of a chitosanase from Bacillus amyloliquefaciens (BamCsn) and the importance of a tryptophan (Trp), W204, for BamCsn activity. BamCsn hydrolyzed the chitosan polymer by an endo mode. It also hydrolyzed chitin oligosaccharides and interestingly exhibited transglycosylation activity on chitotetraose and chitopentaose. Mutation of W204, a nonconserved amino acid in chitosanases, to W204A abolished the hydrolytic activity of BamCsn, with a change in the structure that resulted in a decreased affinity for the substrate and impaired the catalytic ability. Phylogenetic analysis revealed that BamCsn could belong to a new class of chitosanases that showed unique properties like transglycosylation, cleavage of chitin oligosaccharides, and the presence of W204 residues, which is important for activity. Chitosanases belonging to the BamCsn class showed a high potential to generate COS from chitinous substrates.

Selection and mutational analyses of the substrate interacting residues of a chitinase from Enterobacter cloacae subsp. cloacae (EcChi2) to improve transglycosylation

Transglycosylation (TG) by Enterobacter cloacae subsp. cloacae chitinase 2 (EcChi2) has been deciphered by site-directed mutagenesis. EcChi2 originally displayed feeble TG with chitin oligomer with a degree of polymerization (DP4), for a short duration. Based on the 3D modelling and molecular docking analyses, we altered the substrate interactions at the substrate-binding cleft, catalytic center, and catalytic groove of EcChi2 by mutational approach to improve TG. The mutation of W166A and T277A increased TG by EcChi2 and also affected its catalytic efficiency on the polymeric substrates. Whereas, R171A had a drastically decreased hydrolytic activity but, retained TG activity. In the increased hydrolytic activity of the T277A, altered interactions with the substrates played an indirect role in the catalysis. Mutation of the central Asp, in the conserved DxDxE motif, to Ala (D314A) and Asn (D314N) conversion yielded DP5-DP8 TG products. The quantifiable TG products (DP5 and DP6) increased to 8% (D314A) and 7% (D314N), resulting in a hyper-transglycosylating mutant. Mutation of W276A and W398A resulted in the loss of TG activity, indicating that the aromatic residues (W276 and W398) at +1 and +2 subsites are essential for the TG activity of EcChi2.

Purification, characterization and cloning of a chitinase from Stenotrophomonas rhizophila G22

In the presented research the extracellular chitinase of Stenotrophomonas rhizophila G22 was biochemically and molecularly characterized. The studied enzyme was purified from a 72-h bacterial culture about 14 times, with a recovery of 63%. The molecular weight of the purified protein was estimated at 50 kDa by SDS-PAGE. The enzyme showed high activity against colloidal chitin. Significantly lower activities were observed with native chitin powder and chitosan. Adsorption of the enzyme to colloidal chitin and to powdered chitin at the level of 75% and 37%, respectively, was observed after 30 min of reaction. Optimum temperature and pH were 37 °C and 5.9, respectively. The enzyme demonstrated higher activity against nitrophenyl-β d N, N', N″-triacetylchitotriose and approx. 5 times lower activity for 4-nitrophenyl-N, N'-diacetyl-β-d-chitobiose. The enzyme is an endochitinase, which is confirmed by the K _m and V _max values determined in the studies. S. rhizophila G22 endochitinase was inhibited in the presence of cysteine-specific inhibitors, which indicates the role of cysteine moieties in the mechanism of catalysis or in stabilisation of the enzyme molecule. Also Ca²⁺ and Mn²⁺ ions may stabilise the protein's spatial structure. SDS and ions: Fe²⁺, Cu²⁺, Co²⁺, Zn²⁺ inhibited the activity of enzyme. A full-length (2109 bp) gene coding chitinase from S. rhizophila G22 was obtained. Four domains typical for glycoside hydrolase family 18 (GH 18) chitinases were identified: catalytic Gly_18, chitin-binding-ChtBD3, type-III fibronectin-FN3 and polycystic kidney disease domain-PKD domain.

Expression and characterization of two chitinases with synergistic effect and antifungal activity from Xenorhabdus nematophila

Xenorhabdus nematophila HB310 secreted the insecticidal protein toxin complex. Two chitinase genes, chi60 and chi70, were found in X. nematophila toxin complex locus. In order to clarify the function of two chitinases, chi60 and chi70 genes were cloned and expressed in Escherichia coli Transetta (DE3). As a result, we found that the Chi60 and Chi70 belonged to glycoside hydrolases (GH) family 18 with a molecular mass of 65 kDa and 78 kDa, respectively. When colloidal chitin was treated as the substrate, Chi60 and Chi70 were proved to have the highest enzymatic activity at pH 6.0 and 50 °C. Chi60 and Chi70 had obvious growth inhibition effect against the second larvae of Helicoverpa armigera with growth inhibiting rate of 81.99% and 90.51%. Chi70 had synergistic effect with the insecticidal toxicity of Bt Cry 1Ac, but the Chi60 had no synergistic effect with Bt Cry 1Ac. Chi60 and Chi70 showed antifungal activity against Alternaria brassicicola, Verticillium dahliae and Coniothyrium diplodiella. The results increased our understanding of the chitinases produced by X. nematophila and laid a foundation for further studies on the mechanism of the chitinases.