Characterization of a cold-adapted and salt-tolerant exo-chitinase (ChiC) from Pseudoalteromonas sp. DL-6

Biochemical Properties of a Novel Cold-Adapted GH19 Chitinase with Three Chitin-Binding Domains from Chitinilyticum aquatile CSC-1 and Its Potential in Biocontrol of Plant Pathogenic Fungi

GH19 (glycoside hydrolase 19) chitinases play crucial roles in the enzymatic conversion of chitin and biocontrol of phytopathogenic fungi. Herein, a novel multifunctional chitinase of GH19 (CaChi19A), which contains three chitin-binding domains (ChBDs), was successfully cloned from Chitinilyticum aquatile CSC-1 and heterologously expressed in Escherichia coli. We also generated truncated mutants of CaChi19A_ΔI, CaChi19A_ΔIΔII, and CaChi19A_CatD consisting of two ChBDs and a catalytic domain, one ChBD and a catalytic domain, and only a catalytic domain, respectively. CaChi19A, CaChi19A_ΔI, CaChi19A_ΔIΔII, and CaChi19A_CatD exhibited cold adaptation, as their relative enzyme activities at 5 °C were 40.7, 51.6, 66.2, and 82.6%, respectively. Compared with CaChi19A and other variants, CaChi19A_ΔIΔII demonstrated a higher level of stability below 50 °C and retained relatively high activity over a wide pH range of 5-12. Analysis of the hydrolysis products revealed that CaChi19A and CaChi19A_ΔIΔII exhibit exoacting, endoacting, and N-acetyl-β-d-glucosaminidase activities toward colloidal chitin. Furthermore, CaChi19A and CaChi19A_ΔIΔII exhibited inhibitory effects on the hyphal growth of Fusarium oxysporum, Fusarium redolens, Fusarium fujikuroi, Fusarium solani, and Coniothyrium diplodiella, thereby illustrating effective biocontrol activity. These results indicated that CaChi19A and CaChi19A_ΔIΔII show advantages in some applications where low temperatures were demanded in industries as well as the biocontrol of fungal diseases in agriculture.

Separation, purification and structural characterization of marine oligosaccharides: A comprehensive and systematic review of chromatographic methods

Marine oligosaccharides have now been applied in a wide range of industry due to various kinds of physiological activities. However, the oligosaccharides with different polymeric degrees (Dps) differed in physiological activities and applicable fields. So it is promising and essential to separate, purify and structurally characterize these oligosaccharides for understanding their structure-function relationship. This review will summarize the lasted developments in the separation, purification and structural characterization of marine oligosaccharides, including the alginate oligosaccharides, carrageenan oligosaccharides, agar oligosaccharides, chitin oligosaccharides and chitosan oligosaccharides, emphasizing the successful examples of methods for separation and purification. Furthermore, an outlook for preparation of functional oligosaccharides in food biotechnology and agriculture fields is also included. This comprehensive review could definitely promote the utilization of marine functional polysaccharides for food and agriculture.

Chitinolytic and Fungicidal Potential of the Marine Bacterial Strains Habituating Pacific Ocean Regions

Screening for chitinolytic activity in the bacterial strains from different Pacific Ocean regions revealed that the highly active representatives belong to the genera Microbulbifer, Vibrio, Aquimarina, and Pseudoalteromonas. The widely distributed chitinolytic species was Microbulbifer isolated from the sea urchin Strongylocentrotus intermedius. Among seventeen isolates with confirmed chitinolytic activity, only the type strain P. flavipulchra KMM 3630T and the strains of putatively new species Pseudoalteromonas sp. B530 and Vibrio sp. Sgm 5, isolated from sea water (Vietnam mollusc farm) and the sea urchin S. intermedius (Peter the Great Gulf, the Sea of Japan), significantly suppressed the hyphal growth of Aspergillus niger that is perspective for the biocontrol agents' development. The results on chitinolytic activities and whole-genome sequencing of the strains under study, including agarolytic type strain Z. galactanivorans DjiT, found the new functionally active chitinase structures and biotechnological potential.

Synthesis of acylated derivatives of chitosan oligosaccharide and evaluation of their potential antifungal agents on Fusarium oxysporum

Chitosan oligosaccharide (COS) is an important carbohydrate-based biomaterial for synthesizing candidate drugs and biological agents. This study synthesized COS derivatives by grafting acyl chlorides of different alkyl chain lengths (C8, C10, and C12) onto COS molecules and further investigated their physicochemical properties and antimicrobial activity. The COS acylated derivatives were characterized using Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, X-ray diffraction, and thermogravimetric analysis. COS acylated derivatives were successfully synthesized and possessed high solubility and thermal stability. As for the evaluation of antibacterial activity, COS acylated derivatives did not significantly inhibit Escherichia coli and Staphylococcus aureus, but they significantly inhibited Fusarium oxysporum, which was superior to that of COS. Transcriptomic analysis revealed that COS acylated derivatives exerted antifungal activity mainly by downregulating the expression of efflux pumps, disrupting cell wall integrity, and impeding normal cell metabolism. Our findings provided a fundamental theory for the development of environmentally friendly antifungal agents.

Biochemical Properties of a Cold-Active Chitinase from Marine Trichoderma gamsii R1 and Its Application to Preparation of Chitin Oligosaccharides

The enzymatic degradation of different chitin polymers into chitin oligosaccharides (COSs) is of great significance given their better solubility and various biological applications. Chitinase plays a pivotal role in the enzymatic preparation of COSs. Herein, a cold-adapted and efficient chitinase (ChiTg) from the marine Trichoderma gamsii R1 was purified and characterized. The optimal temperature of ChiTg was 40 °C, and the relative activity at 5 °C was above 40.1%. Meanwhile, ChiTg was active and stable from pH 4.0 to 7.0. As an endo-type chitinase, ChiTg exhibited the highest activity with colloidal chitin, then with ball-milled and powdery chitin. In addition, ChiTg showed high efficiency when hydrolyzing colloidal chitin at different temperatures, and the end products were mainly composed of COSs with one to three degrees of polymerization. Furthermore, the results of bioinformatics analysis revealed that ChiTg belongs to the GH18 family, and its acidic surface and the flexible structure of its catalytic site may contribute to its high activity in cold conditions. The results of this study provide a cold-active and efficient chitinase and ideas for its application regarding the preparation of COSs from colloidal chitin.

Trichoderma longibrachiatum T6: A nematocidal activity of endochitinase gene exploration and its function identification

Endochitinase is a natural extracellular protein in Trichoderma longibrachiatum T6, which can degrade the eggshell of Heterodera avenae significantly, however the related genes that coding this protein was rarely characterized. In the present study, the endochitinase 18-5 gene (T6-Echi18-5) of T. longibrachiatum T6 was cloned and sequenced. The expression level of T6-Echi18-5 gene in T. longibrachiatum T6 was induced and increased after the H. avenae cysts inoculation. The full-length cDNA sequence of T6-Echi18-5 was 1671 bp that contained an ORF of 1275 bp, corresponding to 424 amino acids with a 45.9 kDa molecular weight. A single band of 60.04 kDa was detected and identified using SDS-PAGE and Western blot analysis after transferring the T6-Echi18-5 gene to Escherichia coli BL21 Rosetta (DE3). The concentration of purified recombinant T6-Echi18-5 protein was 1.53 mg·ml^-1, and the optimal temperature and pH were 50 °C and 5.0, respectively. The eggshell and content were dissolved and exuded from 4 to10 days after treatment with the purified recombinant T6-Echi18-5 protein. The relative inhibition rate of eggs hatching was 86.79 % at 12 days after treatment. Our study demonstrated the key role of T6-Echi18-5 gene in degrading the H. avenae eggshell and inhibiting the eggs hatching.

Deciphering the thermotolerance of chitinase O from Chitiniphilus shinanonensis by in vitro and in silico studies

Biochemical and biophysical studies revealed that chitinase O from Chitiniphilus shinanonensis (CsChiO) exhibits considerable thermotolerance, possibly due to the formation of a stable structural conformation. CsChiO is an exochitinase with a temperature optimum of 70 °C. The secondary structures of CsChiO and its catalytic domain (Cat-CsChiO) are only marginally affected upon heating up to 90 °C, as revealed by circular dichroism (CD) spectroscopy. Differential scanning calorimetric (DSC) studies revealed that CsChiO exhibits two endothermic transitions at ca. 51 °C (T_m1) and 59 °C (T_m2), whereas Cat-CsChiO shows a single endothermic transition at 52 °C. Together, the CD and DSC analyses suggested that the catalytic domain of CsChiO undergoes a thermotropic transition at ~52 °C from native state to another stable structural conformation. Results from molecular dynamic simulations corroborated that Cat-CsChiO adopts a stable structural conformation above 50 °C by partial unfolding. Thermotolerant CsChiO would be useful for the conversion of chitin, which is highly abundant, to biologically active COS. This study unveiled the adaptability of enzymes/proteins in nature to perform biological functions at elevated temperatures.

A novel thermophilic chitinase directly mined from the marine metagenome using the deep learning tool Preoptem

Chitin is abundant in nature and its degradation products are highly valuable for numerous applications. Thermophilic chitinases are increasingly appreciated for their capacity to biodegrade chitin at high temperatures and prolonged enzyme stability. Here, using deep learning approaches, we developed a prediction tool, Preoptem, to screen thermophilic proteins. A novel thermophilic chitinase, Chi304, was mined directly from the marine metagenome. Chi304 showed maximum activity at 85 ℃, its Tm reached 89.65 ± 0.22℃, and exhibited excellent thermal stability at 80 and 90 °C. Chi304 had both endo- and exo-chitinase activities, and the (GlcNAc)2 was the main hydrolysis product of chitin-related substrates. The product yields of colloidal chitin degradation reached 97% within 80 min, and 20% over 4 days of reaction with crude chitin powder. This study thus provides a method to mine the novel thermophilic chitinase for efficient chitin biodegradation.

Identification and Characterization of Three Chitinases with Potential in Direct Conversion of Crystalline Chitin into N,N′-diacetylchitobiose

Chitooligosaccharides (COSs) have been widely used in agriculture, medicine, cosmetics, and foods, which are commonly prepared from chitin with chitinases. So far, while most COSs are prepared from colloidal chitin, chitinases used in preparing COSs directly from natural crystalline chitin are less reported. Here, we characterize three chitinases, which were identified from the marine bacterium Pseudoalteromonas flavipulchra DSM 14401^T, with an ability to degrade crystalline chitin into (GlcNAc)₂ (N,N’-diacetylchitobiose). Strain DSM 14401 can degrade the crystalline α-chitin in the medium to provide nutrients for growth. Genome and secretome analyses indicate that this strain secretes six chitinolytic enzymes, among which chitinases Chia4287, Chib0431, and Chib0434 have higher abundance than the others, suggesting their importance in crystalline α-chitin degradation. These three chitinases were heterologously expressed, purified, and characterized. They are all active on crystalline α-chitin, with temperature optima of 45–50 °C and pH optima of 7.0–7.5. They are all stable at 40 °C and in the pH range of 5.0–11.0. Moreover, they all have excellent salt tolerance, retaining more than 92% activity after incubation in 5 M NaCl for 10 h at 4 °C. When acting on crystalline α-chitin, the main products of the three chitinases are all (GlcNAc)₂, which suggests that chitinases Chia4287, Chib0431, and Chib0434 likely have potential in direct conversion of crystalline chitin into (GlcNAc)₂.

Cloning, expression, purification and characterization of chitin deacetylase extremozyme from halophilic Bacillus aryabhattai B8W22

Chitin deacetylase (CDA) (EC 3.5.1.41) is a hydrolytic enzyme that belongs to carbohydrate esterase family 4 as per the CAZY database. The CDA enzyme deacetylates chitin into chitosan. As the marine ecosystem is a rich source of chitin, it would also hold the unexplored extremophiles. In this study, an organism was isolated from 40 m sea sediment under halophilic condition and identified as Bacillus aryabhattai B8W22 by 16S rRNA sequencing. The CDA gene from the isolate was cloned and overexpressed in E. coli Rosetta pLysS and purified using a Ni-NTA affinity chromatography. The enzyme was found active on both ethylene glycol chitin (EGC) and chitooligosaccharides (COS). The enzyme characterization study revealed, maximum enzyme velocity at one hour, optimum pH at 7 with 50 mM Tris-HCl buffer, optimum reaction temperature of 30 ºC in standard assay conditions. The co-factor screening affirmed enhancement in the enzyme activity by 142.43 ± 7.13% and 146.88 ± 4.09% with substrate EGC and COS, respectively, in the presence of 2 mM Mg2+. This activity was decreased with the inclusion of EDTA and acetate in the assay solutions. The enzyme was found to be halotolerant; the relative activity increased to 116.98 ± 3.87% and 118.70 ± 0.98% with EGC and COS as substrates in the presence of 1 M NaCl. The enzyme also demonstrated thermo-stability, retaining 87.27 ± 2.85% and 94.08 ± 0.92% activity with substrate EGC and COS, respectively, upon treatment at 50 ºC for 24 h. The kinetic parameters K m, V max, and K cat were 3.06E-05 µg mL-1, 3.06E + 01 µM mg-1 min-1 and 3.27E + 04 s-1, respectively, with EGC as the substrate and 7.14E-07 µg mL-1, 7.14E + 01 µM mg-1 min-1 and 1.40E + 06 s-1, respectively, with COS as the substrate. The enzyme was found to be following Michaelis-Menten kinetics with both the polymeric and oligomeric substrates. In recent years, enzymatic conversion of chitosan is gaining importance due to its known pattern of deacetylation and reproducibility. Thus, this BaCDA extremozyme could be used for industrial production of chitosan polymer as well as chitosan oligosaccharides for biomedical application.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03073-3.

Molecular Characterization of Four Alkaline Chitinases from Three Chitinolytic Bacteria Isolated from a Mudflat

Four chitinases were cloned and characterized from three strains isolated from a mudflat: Aeromonas sp. SK10, Aeromonas sp. SK15, and Chitinibacter sp. SK16. In SK10, three genes, Chi18A, Pro2K, and Chi19B, were found as a cluster. Chi18A and Chi19B were chitinases, and Pro2K was a metalloprotease. With combinatorial amplification of the genes and analysis of the hydrolysis patterns of substrates, Chi18A and Chi19B were found to be an endochitinase and exochitinase, respectively. Chi18A and Chi19B belonged to the glycosyl hydrolase family 18 (GH18) and GH19, with 869 and 659 amino acids, respectively. Chi18C from SK15 belonged to GH18 with 864 amino acids, and Chi18D from SK16 belonged to GH18 with 664 amino acids. These four chitinases had signal peptides and high molecular masses with one or two chitin-binding domains and, interestingly, preferred alkaline conditions. In the activity staining, their sizes were determined to be 96, 74, 95, and 73 kDa, respectively, corresponding to their expected sizes. Purified Chi18C and Chi18D after pET expression produced N,N′-diacetylchitobiose as the main product in hydrolyzing chitooligosaccharides and colloidal chitin. These results suggest that Chi18A, Chi18C, and Chi18D are endochitinases, that Chi19B is an exochitinase, and that these chitinases can be effectively used for hydrolyzing natural chitinous sources.

The discovery and characterization of a novel chitinase with dual catalytic domains from a Qinghai-Tibetan Plateau wetland soil metagenome

A novel chitinase (P1724) was discovered from a Qinghai-Tibetan plateau microbial metagenome. P1724 contains two GH18 family catalytic domains and is phylogenetically distant from any of the chitinases studied. P1724 and its truncated versions, P1724(∆cGH18) and P1724(∆nGH18), were produced in Escherichia coli and characterized. Using colloidal chitin as substrate, the three recombinant proteins showed maximum hydrolytic activities at 40 °C, pH 5.0-6.0 and 0-0.5 M NaCl, and were cold adaptive, as they remained active at 4 °C; their chitinase activities were decreased with the presence of Cu²⁺ and EDTA, but increased with Ba²⁺ and Ca²⁺; they all showed both chitobiosidase and endochitinase activities. Compared to P1724(∆nGH18), P1724 and P1724(∆cGH18) shared more similarities in temperature and pH stabilities, NaCl tolerance, and substrate affinity, suggesting the N-terminal GH18 domain contributed more than the C-terminal GH18 did in biochemical characteristics of P1724. k_cat/K_m value of P1724 was significantly higher than the sum values of P1724(∆cGH18) and P1724(∆nGH18), which indicated that two GH18 domains of P1724 worked cooperatively in degrading chitin. This study has not only broadened the understanding of unknown chitinases in nature but also discussed the strategy of adding additional catalytic domains in enzyme engineering.

Cloning, expression and characterization of a chitinase from Paenibacillus chitinolyticus strain UMBR 0002

Background

Chitinases are enzymes which degrade β-1,4-glycosidid linkages in chitin. The enzymatic degradation of shellfish waste (containing chitin) to chitooligosaccharides is used in industrial applications to generate high-value-added products from such waste. However, chitinases are currently produced with low efficiency and poor tolerance, limiting the industrial utility. Therefore, identifying chitinases with higher enzymatic activity and tolerance is of great importance.

Methods

Primers were designed using the genomic database of Paenibacillus chitinolyticus NBRC 15660. An exochitinase (CHI) was cloned into the recombinant plasmid pET-22b (+) to form pET-22b (+)-CHI, which was transformed into Escherichia coli TOP10 to construct a genomic library. Transformation was confirmed by colony-polymerase chain reaction and electrophoresis. The target sequence was verified by sequencing. Recombinant pET-22b (+)-CHI was transformed into E. coli Rosetta-gami B (DE3) for expression of chitinase. Recombinant protein was purified by Ni-NTA affinity chromatography and enzymatic analysis was carried out.

Results

The exochitinase CHI from P. chitinolyticus strain UMBR 0002 was successfully cloned and heterologously expressed in E. coli Rosetta-gami B (DE3). Purification yielded a 13.36-fold enrichment and recovery yield of 72.20%. The purified enzyme had a specific activity of 750.64 mU mg^-1. The optimum pH and temperature for degradation of colloidal chitin were 5.0 and 45 °C, respectively. The enzyme showed high stability, retaining >70% activity at pH 4.0-10.0 and 25-45 °C (maximum of 90 min). The activity of CHI strongly increased with the addition of Ca²⁺, Mn²⁺, Tween 80 and urea. Conversely, Cu²⁺, Fe³⁺, acetic acid, isoamyl alcohol, sodium dodecyl sulfate and β-mercaptoethanol significantly inhibited enzyme activity. The oligosaccharides produced by CHI from colloidal chitin exhibited a degree of polymerization, forming N-acetylglucosamine (GlcNAc) and (GlcNAc)₂ as products.

Conclusions

This is the first report of the cloning, heterologous expression and purification of a chitinase from P. chitinolyticus strain UMBR 0002. The results highlight CHI as a good candidate enzyme for green degradation of chitinous waste.

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.

The art of adapting to extreme environments: The model system Pseudoalteromonas

Extremophilic microbes have adapted to thrive in ecological niches characterized by harsh chemical/physical conditions such as, for example, very low/high temperature. Living organisms inhabiting these environments have developed peculiar mechanisms to cope with extreme conditions, in such a way that they mark the chemical-physical boundaries of life on Earth. Studying such mechanisms is stimulating from a basic research viewpoint and because of biotechnological applications. Pseudoalteromonas species are a group of marine gamma-proteobacteria frequently isolated from a range of extreme environments, including cold habitats and deep-sea sediments. Since deep-sea floors constitute almost 60% of the Earth's surface and cold temperatures represent the most common of the extreme conditions, the genus Pseudoalteromonas can be considered one of the most important model systems for studying microbial adaptation. Particularly, among all Pseudoalteromonas representatives, P. haloplanktis TAC125 has recently gained a central role. This bacterium was isolated from seawater sampled along the Antarctic ice-shell and is considered one of the model organisms of cold-adapted bacteria. It is capable of thriving in a wide temperature range and it has been suggested as an alternative host for the soluble overproduction of heterologous proteins, given its ability to rapidly multiply at low temperatures. In this review, we will present an overview of the recent advances in the characterization of Pseudoalteromonas strains and, more importantly, in the understanding of their evolutionary and chemical-physical strategies to face such a broad array of extreme conditions. A particular attention will be given to systems-biology approaches in the study of the above-mentioned topics, as genome-scale datasets (e.g. genomics, proteomics, phenomics) are beginning to expand for this group of organisms. In this context, a specific section dedicated to P. haloplanktis TAC125 will be presented to address the recent efforts in the elucidation of the metabolic rewiring of the organisms in its natural environment (Antarctica).

Cloning, purification, and characterization of an organic solvent-tolerant chitinase, MtCh509, from Microbulbifer thermotolerans DAU221

BACKGROUND

The ability to use organic solvents in enzyme reactions offers a number of industrially useful advantages. However, most enzymes are almost completely inactive in the presence of organic solvents. Thus, organic solvent-tolerant enzymes have potential applications in industrial processes.

RESULTS

A chitinase gene from Microbulbifer thermotolerans DAU221 (mtch509) was cloned and expressed in Escherichia coli BL21 (DE3). The molecular weight of the expressed MtCh509 protein was approximately 60 kDa, and it was purified by His-tag affinity chromatography. Enzymatic assays showed that the optimum temperature for MtCh509 chitinase activity was 55 °C, and the enzyme was stable for 2 h at up to 50 °C. The optimum pH for MtCh509 activity was in the sub-acidic range, at pH 4.6 and 5.0. The activity of MtCh509 was maintained in presence of 1 M salt, gradually decreasing at higher concentrations, with residual activity (20%) detected after incubation in 5 M salt. Some organic solvents (benzene, DMSO, hexane, isoamyl alcohol, isopropyl alcohol, and toluene; 10-20%, v/v) increased the reactivity of MtCh509 relative to the aqueous system. When using NAG3, as a substrate, MtCh509 produced NAG2 as the major product, as well as NAG4, demonstrating that MtCh509 has transglycosylation activity. The K m and V max values for MtCh509 using colloidal chitin as a substrate were 9.275 mg/mL and 20.4 U/mg, respectively. Thus, MtCh509 could be used in extreme industrial conditions.

CONCLUSION

The results of the hydrolysate analysis and the observed increase in enzyme activity in the presence of organic solvents show that MtCh509 has industrially attractive advantages. This is the first report on an organic solvent-tolerant and transglycosylating chitinase from Microbulbifer species.

Enzymatic properties of β-N-acetylglucosaminidases

β-N-Acetylglucosaminidases (GlcNAcases) hydrolyse N-acetylglucosamine-containing oligosaccharides and proteins. These enzymes produce N-acetylglucosamine (GlcNAc) and have a wide range of promising applications in the food, energy, and pharmaceutical industries, such as synergistic degradation of chitin with endo-chitinases and using GlcNAc to produce sialic acid, bioethanol, single-cell proteins, and pharmaceutical therapeutics. GlcNAcases also play an important role in the dynamic balance of cellular O-linked GlcNAc levels, catabolism of ganglioside storage in Tay-Sachs disease, and bacterial cell wall recycling and flagellar assembly. In view of these important biological functions and the wide range of industrial applications of GlcNAcases, this review aims to provide a better understanding of various advances for these enzymes. It focuses on enzymatic properties of GlcNAcases, including substrate specificity, catalytic activity, pH optimum, temperature optimum, thermostability, the effects of various metal ions and organic reagents, and transglycosylation.

The inhibition of LPS-induced inflammation in RAW264.7 macrophages via the PI3K/Akt pathway by highly N-acetylated chitooligosaccharide

Chitooligosaccharide (COS) has been shown to regulate many biological functions, such as antimicrobial effect and antitumor activity. In the present study, highly N-acetylated chitooligosaccharide (NACOS) was prepared by N-acetylation of COS, and the anti-inflammatory activity of NACOS in macrophages were evaluated. The results indicated NACOS significantly suppressed the LPS-induced pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) expression. Furthermore, the increased levels of reactive oxygen species (ROS) and nitric oxide (NO) were repressed by NACOS in a dose dependent manner. However, NACOS itself had no significant effect on the cell viability and cellular morphology. Signal transduction studies demonstrated that NACOS remarkably inhibited LPS-enhanced phosphorylation of phosphatidylinositol 3-kinase (PI3K) and Akt. These findings provide a possible molecular mechanism by which NACOS inhibit LPS-induced inflammatory response in macrophages, and a basis for utilizing NACOS in pharmaceutical therapy against inflammation.

Transglycosylation by a chitinase from Enterobacter cloacae subsp. cloacae generates longer chitin oligosaccharides

Humans have exploited natural resources for a variety of applications. Chitin and its derivative chitin oligosaccharides (CHOS) have potential biomedical and agricultural applications. Availability of CHOS with the desired length has been a major limitation in the optimum use of such natural resources. Here, we report a single domain hyper-transglycosylating chitinase, which generates longer CHOS, from Enterobacter cloacae subsp. cloacae 13047 (EcChi1). EcChi1 was optimally active at pH 5.0 and 40 °C with a K_m of 15.2 mg ml⁻¹, and k_cat/K_m of 0.011× 10² mg⁻¹ ml min⁻¹ on colloidal chitin. The profile of the hydrolytic products, major product being chitobiose, released from CHOS indicated that EcChi1 was an endo-acting enzyme. Transglycosylation (TG) by EcChi1 on trimeric to hexameric CHOS resulted in the formation of longer CHOS for a prolonged duration. EcChi1 showed both chitobiase and TG activities, in addition to hydrolytic activity. The TG by EcChi1 was dependent, to some extent, on the length of the CHOS substrate and concentration of the enzyme. Homology modeling and docking with CHOS suggested that EcChi1 has a deep substrate-binding groove lined with aromatic amino acids, which is a characteristic feature of a processive enzyme.