Cloning, Expression and 3D Structure Prediction of Chitinase from Chitinolyticbacter meiyuanensis SYBC-H1

A novel bi-functional cold-adaptive chitinase from Chitinilyticum aquatile CSC-1 for efficient synthesis of N-acetyl-D-glucosaminidase

In order to better utilize chitinolytic enzymes to produce high-value N-acetyl-D-glucosamine (GlcNAc) from chitinous waste, there is an urgent need to explore bi-functional chitinases with exceptional properties of temperature, pH and metal tolerance. In this study, we cloned and characterized a novel bi-functional cold-adaptive chitinase called CaChi18A from a newly isolated strain, Chitinilyticum aquatile CSC-1, in Bama longevity village of Guangxi Province, China. The activity of CaChi18A at 50 °C was 4.07 U/mg. However, it exhibited significant catalytic activity even at 5 °C. Its truncated variant CaChi18A_ΔChBDs, containing only catalytic domain, demonstrated significant activity levels, exceeding 40 %, over a temperature range of 5-60 °C and a pH range of 3 to 10. It was noteworthy that it displayed tolerance towards most metal ions at a final concentration of 0.1 mM, including Fe3+ and Cu2+ ions, retaining 122.52 ± 0.17 % and 116.42 ± 1.52 % activity, respectively. Additionally, it exhibited favorable tolerance towards organic solvents with the exception of formic acid. Interestedly, CaChi18A and CaChi18A_ΔChBDs had a low Km value towards colloidal chitin (CC), 0.94 mg mL-1 and 2.13 mg mL-1, respectively. Both enzymes exhibited chitobiosidase and N-acetyl-D-glucosaminidase activities, producing GlcNAc as the primary product when hydrolyzing CC. The high activities across a broader temperature and pH range, strong environmental adaptability, and hydrolytic properties of CaChi18A_ΔChBDs suggested that it could be a promising candidate for GlcNAc production.

A novel endo-type chitinase possessing chitobiase activity derived from the chitinolytic bacterium, Chitiniphilus shinanonensis SAY3T

One of the chitinases (ChiG) derived from the chitinolytic bacterium Chitiniphilus shinanonensis SAY3T exhibited chitobiase activity cleaving dimers of N-acetyl-D-glucosamine (GlcNAc) into monomers, which is not detected in typical endo-type chitinases. Analysis of the reaction products for GlcNAc hexamers revealed that all the five internal glycosidic bonds were cleaved at the initial stage. The overall reaction catalyzed by chitobiases toward GlcNAc dimers was similar to that catalyzed by N-acetyl-D-glucosaminidases (NAGs). SAY3 possesses two NAGs (ChiI and ChiT) that are thought to be important in chitin catabolism. Unexpectedly, a triple gene-disrupted mutant (ΔchiIΔchiTΔchiG) was still able to grow on synthetic medium containing GlcNAc dimers or powdered chitin, similar to the wild-type SAY3, although it exhibited only 3% of total cellular NAG activity compared to the wild-type. This indicates the presence of unidentified enzyme(s) capable of supporting normal bacterial growth on the chitin medium by NAG activity compensation.

Efficient production of GlcNAc in an aqueous-organic system with a Chitinolyticbacter meiyuanensis SYBC-H1 mutant

OBJECTIVES

Shellfish waste is a primary source for making N-acetyl-D-glucosamine. Thus, establishing a high-efficiency and low-cost bioconversion method to produce N-acetyl-D-glucosamine directly from shellfish waste was promising.

RESULTS

A mutant C81 was obtained from Chitinolyticbacter meiyuanensis SYBC-H1 via ⁶⁰Co-γ irradiation. This mutant C81 showed the highest chitinase activity of 9.8 U/mL that was 85% higher than the parent strain. The mutant C81 exhibted improved antioxidant activities, including total antioxidant capacity, superoxide radical ability, and hydroxyl radical scavenging ability, compared to that of the parent strain. Four out of nine organic solvents increased the chitinase activity by 1.9%, 6.8%, 11.7%, and 15.8%, corresponding to methylbenzene, n-heptane, petroleum ether, and n-hexane, respectively. The biphase system composed of aqueous and hexane presented a five-fold reduction of cell viability compared to the control. Using a continuous fermentation bioconversion process, 4.2 g/L GlcNAc was produced from crayfish shell powder with a yield of 80% of the chitin content.

CONCLUSIONS

This study demonstrated that the mutant C81 is suitable for converting crayfish shell powder into GlcNAc in an aqueous-organic system.

Novel Bi-Modular GH19 Chitinase with Broad pH Stability from a Fibrolytic Intestinal Symbiont of Eisenia fetida, Cellulosimicrobium funkei HY-13

Endo-type chitinase is the principal enzyme involved in the breakdown of N-acetyl-d-glucosamine-based oligomeric and polymeric materials through hydrolysis. The gene (966-bp) encoding a novel endo-type chitinase (ChiJ), which is comprised of an N-terminal chitin-binding domain type 3 and a C-terminal catalytic glycoside hydrolase family 19 domain, was identified from a fibrolytic intestinal symbiont of the earthworm Eisenia fetida, Cellulosimicrobium funkei HY-13. The highest endochitinase activity of the recombinant enzyme (rChiJ: 30.0 kDa) toward colloidal shrimp shell chitin was found at pH 5.5 and 55 °C and was considerably stable in a wide pH range (3.5–11.0). The enzyme exhibited the highest biocatalytic activity (338.8 U/mg) toward ethylene glycol chitin, preferentially degrading chitin polymers in the following order: ethylene glycol chitin > colloidal shrimp shell chitin > colloidal crab shell chitin. The enzymatic hydrolysis of N-acetyl-β-d-chitooligosaccharides with a degree of polymerization from two to six and colloidal shrimp shell chitin yielded primarily N,N′-diacetyl-β-d-chitobiose together with a small amount of N-acetyl-d-glucosamine. The high chitin-degrading ability of inverting rChiJ with broad pH stability suggests that it can be exploited as a suitable biocatalyst for the preparation of N,N′-diacetyl-β-d-chitobiose, which has been shown to alleviate metabolic dysfunction associated with type 2 diabetes.

Biochemical characterization of a GH19 chitinase from Streptomyces alfalfae and its applications in crystalline chitin conversion and biocontrol

Chitinases play crucial roles in enzymatic conversion of chitin and biocontrol of phytopathogenic fungi. Herein, a chitinase of glycoside hydrolase (GH) family 19, SaChiB, was cloned from Streptomyces alfalfae ACCC 40021 and expressed in Escherichia coli BL21(DE3). The purified SaChiB displayed maximal activities at 45 °C and pH 8.0, and showed good stability up to 55 °C and in the range of pH 4.0-11.0, respectively. It exhibited substrate specificity towards chitin and chitooligosaccharides (degree of polymerization 3-6) with the endo-cleavage manner. In combination with the N-acetyl hexosaminidase SaHEX, it yielded a conversion rate of 95.2% from chitin powder to N-acetyl-D-glucosamine in 8 h and a product purity of >98.5%. Furthermore, the enzyme strongly inhibited the growth of tested pathogenic fungi. These results indicated that SaChiB has the great potential for applications in the conversion of raw chitinous waste in industries as well as the biocontrol of fungal diseases in agriculture.

Molecular characterization of a novel chitinase CmChi1 from Chitinolyticbacter meiyuanensis SYBC-H1 and its use in N-acetyl-d-glucosamine production

BACKGROUND

N-acetyl-d-glucosamine (GlcNAc) possesses many bioactivities that have been used widely in many fields. The enzymatic production of GlcNAc is eco-friendly, with high yields and a mild production process compared with the traditional chemical process. Therefore, it is crucial to discover a better chitinase for GlcNAc production from chitin.

RESULTS

A novel chitinase gene (Cmchi1) cloned from Chitinolyticbacter meiyuanensis SYBC-H1 and expressed in Escherichia coli BL21(DE3) cells. The recombinant enzyme (CmChi1) contains a glycosyl hydrolase family 18 catalytic module that shows low identity (12-27%) with the corresponding domain of the well-characterized chitinases. CmChi1 was purified with a recovery yield of 89% by colloidal chitin affinity chromatography, whereupon it had a specific activity of up to 15.3 U/mg. CmChi1 had an approximate molecular mass of 70 kDa after the sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and its optimum activity for colloidal chitin (CC) hydrolysis occurred at pH 5.2 and 50 °C. Furthermore, CmChi1 exhibited k_cat/K_m values of 7.8 ± 0.11 mL/s/mg and 239.1 ± 2.6 mL/s/μmol toward CC and 4-nitrophenol N,N'-diacetyl-β-d-chitobioside [p-NP-(GlcNAc)₂], respectively. Analysis of the hydrolysis products revealed that CmChi1 exhibits exo-acting, endo-acting and N-acetyl-β-d-glucosaminidase activities toward N-acetyl chitooligosaccharides (N-acetyl CHOS) and CC substrates, behavior that makes it different from typical reported chitinases. As a result, GlcNAc could be produced by hydrolyzing CC using recombinant CmChi1 alone with a yield of nearly 100% and separated simply from the hydrolysate with a high purity of 98%.

CONCLUSION

The hydrolytic properties and good environmental adaptions indicate that CmChi1 has excellent potential in commercial GlcNAc production. This is the first report on exo-acting, endo-acting and N-acetyl-β-d-glucosaminidase activities from Chitinolyticbacter species.

Mining and characterization of two novel chitinases from Hirsutella sinensis using an efficient transcriptome-mining approach

Two novel family 18 chitinases, chiA and chiH, were identified and cloned from the transcriptome of H. sinensis based on the transcriptome sequence data. The recombinant chitinases were overexpressed in Escherichia coli BL21, subsequently purified and functionally characterized. The optimal temperature and pH for chiA were 55 °C and 5.0, respectively, and those for chiH were 50 °C and 5.0, respectively. The highest enzyme activities of 11.5 U/mg and 8.1 U/mg were obtained for chiA and chiH, respectively, when colloidal chitin was used as the substrate with Ba²⁺. chiA exhibited higher V_max of 1.94 μmol/μg/h and k_cat of 1.443 S^-1 than those of chiH with V_max of 1.63 μmol/μg/h and k_cat of 1.175 S^-1, and both were efficient towards colloidal chitin compared with other typical family 18 chitinases. Substrate specificity and gene expression analyses indicated that chiA and chiH preferred substrates containing N-acetyl groups, such as colloidal chitin and glycol chitin, while no activity was detected toward laminarin, cellobiose, carboxymethyl cellulose and starch. The work presented here would aid in the understanding and performance of future studies on the infection mechanism of H. sinensis.