Multiple chitinases of an endophytic Serratia proteamaculans 568 generate chitin oligomers

Response surface optimization, purification, characterization and short-chain chitooligosaccharides production from an acidic, thermostable chitinase from Thermomyces dupontii

Chitin, recovered in huge amounts from coastal waste, may biocatalytically valorized for utilization in food and biotech sectors. Conventional chemical-based conversion makes use of significant volumes of hazardous acid and alkali. Alternatively, enzymes offer better process control and generation of homogeneous products. Process variables were derived to achieve augmented levels of chitinase (3.8809 Ul-1 h-1) productivity from a novel thermophilic fungal strain Thermomyces dupontii, ITCC 9104 following incubation (96 h, 45 °C). An acidic thermostable chitinase TdChiT having molecular mass of 60 kDa has been purified. Optimal TdChiT activity has been demonstrated at 70 °C and pH 5. Notably decreased activity over a broad range of temperature and pH was observed following deglycosylation. Half-life, activation energy, Gibbs free energy, enthalpy and entropy for denaturation of TdChiT at its optimum temperature were 197.40 min, 105.48 kJ mol-1, 100.59 kJ mol-1, 102.64 kJ mol-1 and 5.95 J mol-1 K-1. TdChiT has specificity towards colloidal chitin and (GlcNAc)2-4. Metal ions viz. Mn2+, Ca2+ and Co2+ and nonionic surfactants notably enhanced chitinase activity. Thin layer chromatography analysis has revealed effective hydrolysis of colloidal chitin and (GlcNAc)2-4. TdChiT may potentially be employed for design of better, eco-friendly and less resource-intensive industrial procedures for upcycling of crustacean waste into value-added organonitrogens.

Insights into Chitin-Degradation Potential of Shewanella khirikhana JW44 with Emphasis on Characterization and Function of a Chitinase Gene SkChi65

Chitin, a polymer of β-1,4-linked N-acetylglucosamine (GlcNAc), can be degraded into valuable oligosaccharides by various chitinases. In this study, the genome of Shewanella khirikhana JW44, displaying remarkable chitinolytic activity, was investigated to understand its chitin-degradation potential. A chitinase gene SkChi65 from this strain was then cloned, expressed, and purified to characterize its enzymatic properties and substrate hydrolysis. Genome analysis showed that, of the 14 genes related to chitin utilization in JW44, six belonged to glycoside hydrolase (GH) families because of their functional domains for chitin binding and catalysis. The recombinant chitinase SkChi65, consisting of 1129 amino acids, was identified as a member of the GH18 family and possessed two chitin-binding domains with a typical motif of [A/N]KWWT[N/S/Q] and one catalytic domain with motifs of DxxDxDxE, SxGG, YxR, and [E/D]xx[V/I]. SkChi65 was heterologously expressed as an active protein of 139.95 kDa best at 37 °C with 1.0 mM isopropyl-β-d-thiogalactopyranoside induction for 6 h. Purified SkChi65 displayed high stability over the ranges of 30-50 °C and pH 5.5-8.0 with optima at 40 °C and pH 7.0. The kinetic parameters Km, Vmax, and kcat of SkChi65 towards colloidal chitin were 27.2 μM, 299.2 μMs-1, and 10,203 s-1, respectively. In addition to colloidal chitin, SkChi65 showed high activity towards glycol chitosan and crystalline chitin. After analysis by thin-layer chromatography, the main products were N,N'-diacetylchitobiose, and GlcNAc with (GlcNAc)2-6 used as substrates. Collectively, SkChi65 could exhibit both exo- and endochitinase activities towards diverse substrates, and strain JW44 has a high potential for industrial application with an excellent capacity for chitin bioconversion.

Characterization of a New Multifunctional GH20 β-N-Acetylglucosaminidase From Chitinibacter sp. GC72 and Its Application in Converting Chitin Into N-Acetyl Glucosamine

In this study, a gene encoding β-N-acetylglucosaminidase, designated NAGaseA, was cloned from Chitinibacter sp. GC72 and subsequently functional expressed in Escherichia coli BL21 (DE3). NAGaseA contains a glycoside hydrolase family 20 catalytic domain that shows low identity with the corresponding domain of the well-characterized NAGases. The recombinant NAGaseA had a molecular mass of 92 kDa. Biochemical characterization of the purified NAGaseA revealed that the optimal reaction condition was at 40°C and pH 6.5, and exhibited great pH stability in the range of pH 6.5-9.5. The V ma x , K m, k cat, and k cat /K m of NAGaseA toward p-nitrophenyl-N-acetyl glucosaminide (pNP-GlcNAc) were 3333.33 μmol min-1 l-1, 39.99 μmol l-1, 4667.07 s-1, and 116.71 ml μmol-1 s-1, respectively. Analysis of the hydrolysis products of N-acetyl chitin oligosaccharides (N-Acetyl COSs) indicated that NAGaseA was capable of converting N-acetyl COSs ((GlcNAc)2-(GlcNAc)6) into GlcNAc with hydrolysis ability order: (GlcNAc)2 > (GlcNAc)3 > (GlcNAc)4 > (GlcNAc)5 > (GlcNAc)6. Moreover, NAGaseA could generate (GlcNAc)3-(GlcNAc)6 from (GlcNAc)2-(GlcNAc)5, respectively. These results showed that NAGaseA is a multifunctional NAGase with transglycosylation activity. In addition, significantly synergistic action was observed between NAGaseA and other sources of chitinases during hydrolysis of colloid chitin. Finally, 0.759, 0.481, and 0.986 g/l of GlcNAc with a purity of 96% were obtained using three different chitinase combinations, which were 1.61-, 2.36-, and 2.69-fold that of the GlcNAc production using the single chitinase. This observation indicated that NAGaseA could be a potential candidate enzyme in commercial GlcNAc production.

Purification and characterization of chitinase produced by thermophilic fungi Thermomyces lanuginosus

BACKGROUND

In the past few years, the production of shrimp shell waste from the seafood processing industries has confronted a significant surge. Furthermore, insignificant dumping of waste has dangerous effects on both nature and human well-being. This marine waste contains a huge quantity of chitin which has several applications in different fields. The chitinase enzyme can achieve degradation of chitin, and the chitin itself can be used as the substrate as well for production of chitinase. In the current study, the chitinase enzyme was produced by Thermomyces lanuginosus. The extracellular chitinase was purified from crude extract using ammonium sulfate precipitation followed by DEAE-cellulose ion-exchange chromatography and Sephadex G-100 gel filtration chromatography. The stability and activity of chitinase with different pH, temperature, different times for a reaction, in the presence of different metal ions, and different concentration of enzyme and substrate were analyzed.

RESULT

The chitinase activity was found to be highest at pH 6.5, 50 °C, and 60 min after the reaction began. and the chitinase showed the highest activity and stability in the presence of β-mercaptoethanol (ME). The SDS-PAGE of denatured purified chitinase showed a protein band of 18 kDa.

CONCLUSION

The characterization study concludes that Cu²⁺, Hg²⁺, and EDTA have an inhibitory effect on chitinase activity, whereas β-ME acts as an activator for chitinase activity. The utilization of chitin to produce chitinase and the degradation of chitin using that chitinase enzyme would be an opportunity for bioremediation of shrimp shell waste.

Chemoenzymatic production of chitooligosaccharides employing ionic liquids and Thermomyces lanuginosus chitinase

The aim of this work was to study a two-step chemoenzymatic method for production of short chain chitooligosaccharides. Chitin was chemically pretreated using sulphuric acid, sodium hydroxide and two different ionic liquids, 1-Ethyl-3-methylimidazolium bromide and Trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate under mild processing conditions. Pretreated chitin was further hydrolyzed employing purified chitinase from Thermomyces lanuginosus ITCC 8895. Trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate treated chitin appeared amorphous and resulted in generation of 1.10 ± 0.89 mg ml^-1 of (GlcNAc)₂ and 1.07 ± 0.92 mg ml^-1 of (GlcNAc)₃. Further derivation of optimum conditions through two-factor-9 run experiments resulted in to 1.5 and 1.3 fold increments in (GlcNAc)₂ and (GlcNAc)₃ production, respectively. 0.1 g of both (GlcNAc)₂ and (GlcNAc)₃ has been purified from the Trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate pretreated chitin (1 g) employing cation exchange chromatography. The present study will lay the foundation for development of a green sustainable solution for cost effective upcycling of coastal residual resources to chito-bioactives.

Enhanced Chitin Deacetylase Production Ability of Rhodococcus equi CGMCC14861 by Co-culture Fermentation With Staphylococcus sp. MC7

Chitin deacetylase (CDA) can hydrolyze the acetamido group of chitin polymers and its deacetylated derivatives to produce chitosan, an industrially important biopolymer. Compared with traditional chemical methods, biocatalysis by CDA is more environment-friendly and easy to control. However, most reported CDA-producing microbial strains show low CDA producing capabilities. Thus, the enhancement of CDA production has always been a challenge. In this study, we report co-culture fermentation to significantly promote the CDA production of Rhodococcus equi CGMCC14861 chitin deacetylase (ReCDA). Due to co-culture fermentation with Staphylococcus sp. MC7, ReCDA yield increased to 21.74 times that of pure culture of R. equi. Additionally, the enhancement was demonstrated to be cell-independent by adding cell-free extracts and the filtrate obtained by 10 kDa ultrafiltration of Staphylococcus sp. MC7. By preliminary characterization, we found extracellular, thermosensitive signal substances produced by Staphylococcus that were less than 10 kDa. We investigated the mechanism of promotion of ReCDA production by transcriptomic analysis. The data showed that 328 genes were upregulated and 1,258 genes were downregulated. The transcription level of the gene encoding ReCDA increased 2.3-fold. These findings provide new insights into the research of co-culture fermentation for the production of CDA and quorum sensing regulation.

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.

Catalytic efficiency of a multi-domain transglycosylating chitinase from Enterobacter cloacae subsp. cloacae (EcChi2) is influenced by polycystic kidney disease domains

Bacterial chitinases recruited multiple accessory domains for the conversion of recalcitrant polysaccharides to simple soluble sugars/amino sugars. Here, we report detailed properties of a multi-domain GH18 chitinase from Enterobacter cloacae subsp. cloacae (EcChi2) that preferred β-chitin as substrate. EcChi2 exhibited transglycosylation (TG) activity on oligomeric substrates from DP4-DP6. The high amount of DP2 is indicative of exo mode activity of EcChi2. We generated EcChi2 variants (truncated and fusion chimeras) and elucidated the role of catalytic and accessory domains. The catalytic efficiency of truncated GH18 and fusion chimera of GH18+ChBD1-ChBD2 decreased to 22 and 17-fold, respectively, than EcChi2, and lost the hydrolytic activity on polymeric substrates, except colloidal chitin. On the other hand, the catalytic activity of truncated PKD1-GH18-PKD2 on polymeric and oligomeric substrates was similar to EcChi2, suggesting that PKD domains are essential for increasing the rate of hydrolysis. Moreover, the truncated ChBD1-ChBD2 and fusion PKD1 + PKD2 participated in chitin-binding.

A holin/peptidoglycan hydrolase-dependent protein secretion system

Gram-negative bacteria have evolved numerous pathways to secrete proteins across their complex cell envelopes. Here, we describe a protein secretion system that uses a holin membrane protein in tandem with a cell wall-editing enzyme to mediate the secretion of substrate proteins from the periplasm to the cell exterior. The identity of the cell wall-editing enzymes involved was found to vary across biological systems. For instance, the chitinase secretion pathway of Serratia marcescens uses an endopeptidase to facilitate secretion, whereas the secretion of Typhoid toxin in Salmonella enterica serovar Typhi relies on a muramidase. Various families of holins are also predicted to be involved. Genomic analysis indicates that this pathway is conserved and implicated in the secretion of hydrolytic enzymes and toxins for a range of bacteria. The pairing of holins from different families with various types of peptidoglycan hydrolases suggests that this secretion pathway evolved multiple times. We suggest that the complementary bodies of evidence presented is sufficient to propose that the pathway be named the Type 10 Secretion System (TXSS).

Structural Insight Into Chitin Degradation and Thermostability of a Novel Endochitinase From the Glycoside Hydrolase Family 18

Bacterial endochitinases play important roles in environmental chitin degradation and have good applications. Although the structures of some endochitinases, most belonging to the glycoside hydrolase (GH) family 18 and thermostable, have been reported, the structural basis of these enzymes for chitin degradation still remain unclear due to the lack of functional confirmation, and the molecular mechanism for their thermostability is also unknown. Here, we characterized a GH18 endochitinase, Chi23, from marine bacterium Pseudoalteromonas aurantia DSM6057, and solved its structure. Chi23 is a thermostable enzyme that can non-processively hydrolyze crystalline and colloidal chitin. Chi23 contains only a catalytic domain that adopts a classical (β/α)₈ TIM-barrel fold. Compared to other GH18 bacterial endochitinases, Chi23 lacks the chitin-binding domain and the β-hairpin subdomain, indicating that Chi23 has a novel structure. Based on structural analysis of Chi23 docked with (GlcNAc)₅ and mutational analysis, the key catalytic residue (Glu117) and seven substrate-binding residues (Asn9, Gln157, Tyr189, Asn190, Asp229, Trp260, and Gln261) are revealed. Among these identified residues, Asn9, Asp229 and Gln261 are unique to Chi23, and their cumulative roles contribute to the activity of Chi23 against both crystalline and soluble chitin. Five substrate-binding residues (Tyr189, Asn190, Asp229, Trp260, and Gln261) are found to play important roles in maintaining the thermostability of Chi23. In particular, hydrogen bond networks involving Asp229 and Gln261 are formed to stabilize the protein structure of Chi23. Phylogenetic analysis indicated that Chi23 and its homologs represent a new group of GH18 endochitinases, which are widely distributed in bacteria. This study sheds light on the molecular mechanism of a GH18 endochitinase for chitin degradation.

Structural and Thermodynamic Signatures of Ligand Binding to the Enigmatic Chitinase D of Serratia proteamaculans

The Gram-negative bacteria Serratia marcescens and Serratia proteamaculans have efficient chitinolytic machineries that degrade chitin into N-acetylglucosamine (GlcNAc), which is used as a carbon and energy source. The enzymatic degradation of chitin in these bacteria occurs through the synergistic action of glycoside hydrolases (GHs) that have complementary activities; an endo-acting GH (ChiC) making random scissions on the polysaccharide chains and two exo-acting GHs mainly targeting single reducing (ChiA) and nonreducing (ChiB) chain ends. Both bacteria produce low amounts of a fourth GH18 (ChiD) with an unclear role in chitin degradation. Here, we have determined the thermodynamic signatures for binding of (GlcNAc)₆ and the inhibitor allosamidin to SpChiD as well as the crystal structure of SpChiD in complex with allosamidin. The binding free energies for the two ligands are similar (Δ G_r° = -8.9 ± 0.1 and -8.4 ± 0.1 kcal/mol, respectively) with clear enthalpic penalties (Δ H_r° = 3.2 ± 0.1 and 1.8 ± 0.1 kcal/mol, respectively). Binding of (GlcNAc)₆ is dominated by solvation entropy change (- TΔ S_solv° = -17.4 ± 0.4 kcal/mol) and the conformational entropy change dominates for allosamidin binding (- TΔ S_conf° = -9.0 ± 0.2 kcal/mol). These signatures as well as the interactions with allosamidin are very similar to those of SmChiB suggesting that both enzymes are nonreducing end-specific.

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.

Bioconversion of chitosan into chito-oligosaccharides (CHOS) using family 46 chitosanase from Bacillus subtilis (BsCsn46A)

BsCsn46A, a GH family 46 chitosanase from Bacillus subtilis had been previously shown to have potential for bioconversion of chitosan to chito-oligosaccharides (CHOS). However, so far, in-depth analysis of both the mode of action of this enzyme and the composition of its products were lacking. In this study, we have employed size exclusion chromatography, ¹H NMR, and mass spectrometry to reveal that BsCsn46A can rapidly cleave chitosans with a wide-variety of acetylation degrees, using a non-processive endo-mode of action. The composition of the product mixtures can be tailored by varying the degree of acetylation of the chitosan and the reaction time. Detailed analysis of product profiles revealed differences compared to other chitosanases. Importantly, BsCsn46A seems to be one of the fastest chitosanases described so far. The detailed analysis of preferred endo-binding modes using H₂¹⁸O showed that a hexameric substrate has three productive binding modes occurring with similar frequencies.

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.

Production of chitinase from thermophilic Humicola grisea and its application in production of bioactive chitooligosaccharides

A novel thermophilic chitinase producing strain Humicola grisea ITCC 10,360.16 was isolated from soil of semi-arid desert region of Rajasthan. Maximum enzyme production (116±3.45Ul^-1) was achieved in submerged fermentation. Nutritional requirement for maximum production of chitinase under submerged condition was optimized using response surface methodology. Among the eight nutritional elements studied, chitin, colloidal chitin, KCl and yeast-extract were identified as the most critical variables for chitinase production by Plackett-Burman design first. Further optimization of these variables was done by four-factor central composite design. The model came out to be significant and statistical analysis of results showed that an appropriate ratio of chitin and colloidal chitin had resulted into enhancement in enzyme production levels. Optimum concentration of the variables for enhanced chitinase production were 7.49, 4.91, 0.19 and 5.50 (gl^-1) for chitin, colloidal chitin, KCl and yeast extract, respectively. 1.43 fold enhancement in chitinase titres was attained in shake flasks, when the variables were used at their optimum levels. Thin layer chromatography revealed that enzyme can effectively hydrolyze colloidal chitin to produce chitooligosaccharides. Chitinase production from H. grisea and optimization of economic production medium heighten the employment of enzyme for large scale production of bioactive chitooligosaccharides.

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.

A new chitinase-D from a plant growth promoting Serratia marcescens GPS5 for enzymatic conversion of chitin

The current study describes heterologous expression and biochemical characterization of single-modular chitinase-D from Serratia marcescens (SmChiD) with unprecedented catalytic properties which include chitobiase and transglycosylation (TG) activities besides hydrolytic activity. Without accessory domains, SmChiD, hydrolyzed insoluble polymeric chitin substrates like colloidal, α- and β-chitin. Activity studies on CHOS with degree of polymerization (DP) 2-6 as substrate revealed that SmChiD hydrolyzed DP2 with a chitobiase activity and showed TG activity on CHOS with DP3-6, producing longer chain CHOS. But, the TG products were further hydrolyzed to shorter chain CHOS with DP1-2 products. SmChiD with its unique catalytic properties, could be a potential enzyme for the production of long chain CHOS and also for the preparation of efficient enzyme cocktails for chitin degradation.

Production of N-Acetyl-d-glucosamine from Mycelial Waste by a Combination of Bacterial Chitinases and an Insect N-Acetyl-d-glucosaminidase

N-Acetyl-d-glucosamine (GlcNAc) has great potential to be used as a food additive and medicine. The enzymatic degradation of chitin-containing biomass for producing GlcNAc is an eco-friendly approach but suffers from a high cost. The economical efficiency can be improved by both optimizing the member and ratio of the chitinolytic enzymes and using new inexpensive substrates. To address this, a novel combination of bacterial and insect chitinolytic enzymes was developed in this study to efficiently produce GlcNAc from the mycelia of Asperillus niger, a fermentation waste. This enzyme combination contained three bacterial chitinases (chitinase A from Serratia marcescens (SmChiA), SmChiB, SmChiC) and one insect N-acetyl-d-glucosaminidase from Ostrinia furnacalis (OfHex1) in a ratio of 39.1% of SmChiA, 26.7% of SmChiB, 32.9% of SmChiC, and 1.3% of OfHex1. A yield of 6.3 mM (1.4 mg/mL) GlcNAc with a purity of 95% can be obtained from 10 mg/mL mycelial powder in 24 h. The enzyme combination reported here exhibited 5.8-fold higher hydrolytic activity over the commercial chitinase preparation derived from Streptomyces griseus.

Biochemical Characterization of a Novel Acidic Exochitinase from Rhizomucor miehei with Antifungal Activity

A novel chitinase gene (RmChi44) from Rhizomucor miehei was cloned and expressed in Escherichia coli as an intracellular soluble and active protein. The recombinant chitinase (RmChi44) was purified to homogeneity and biochemically characterized. The molecular mass of RmChi44 was estimated to be 44.6 kDa on SDS-PAGE. RmChi44 displayed an acidic pH optimum of 4.5 and was stable within pH 4.5-9.0. The optimal temperature of RmChi44 was found to be 50 °C. The Km values of RmChi44 for colloidal chitin and glycol chitin were 4.02 and 1.55 mg/mL, respectively. RmChi44 hydrolyzed colloidal chitin to yield mainly N-acetyl chitobiose, exhibiting an exotype cleavage pattern. Moreover, the enzyme displayed β-N-acetylglucosaminidase activity, splitting N-acetyl COSs with degree of polymerization (DP) 2-5 into their monomer. In addition, RmChi44 showed antifungal activity against some phytopathogenic fungi. This is the first report on an exochitinase showing β-N-acetylglucosaminidase activity and antifungal activity from Rhizomucor species.

Production of bioactive chitosan oligosaccharides using the hypertransglycosylating chitinase-D from Serratia proteamaculans

The biological activities of chitosan and its oligosaccharides are greatly influenced by properties such as the degree of polymerization (DP), degree of acetylation (DA) and pattern of acetylation (PA). Here, structurally diverse chitosan oligosaccharides from chitosan polymers (DA=35% or 61%) were generated using Serratia proteamaculans wild-type chitinase D (SpChiD) and the W114A mutant which lacks transglycosylase activity. The crude oligosaccharide mixtures and purified fractions with specific DP and DA ranges were tested for their ability to induce an oxidative burst in rice cell suspension cultures. The crude mixtures were more active when produced by the W114A mutant whereas the purified fractions were more active when produced by wild-type SpChiD. Neither hydrolysis nor transglycosylation by SpChiD was inhibited in the presence of fully-deacetylated oligosaccharides, suggesting that SpChiD could be exploited to generate oligosaccharides with defined DA and PA values.

Catalytic efficiency of chitinase-D on insoluble chitinous substrates was improved by fusing auxiliary domains

Chitin is an abundant renewable polysaccharide, next only to cellulose. Chitinases are important for effective utilization of this biopolymer. Chitinase D from Serratia proteamaculans (SpChiD) is a single domain chitinase with both hydrolytic and transglycosylation (TG) activities. SpChiD had less of hydrolytic activity on insoluble polymeric chitin substrates due to the absence of auxiliary binding domains. We improved catalytic efficiency of SpChiD in degradation of insoluble chitin substrates by fusing with auxiliary domains like polycystic kidney disease (PKD) domain and chitin binding protein 21 (CBP21). Of the six different SpChiD fusion chimeras, two C-terminal fusions viz. ChiD+PKD and ChiD+CBP resulted in improved hydrolytic activity on α- and β-chitin, respectively. Time-course degradation of colloidal chitin also confirmed that these two C-terminal SpChiD fusion chimeras were more active than other chimeras. More TG products were produced for a longer duration by the fusion chimeras ChiD+PKD and PKD+ChiD+CBP.

The role of the chi1 gene from the endophytic bacteria Serratia proteamaculans 336x in the biological control of wheat take-all

Take-all, a disease caused by the fungus Gaeumannomyces graminis var. tritici, is the most important root disease of wheat and causes severe yield losses worldwide. Using microorganisms as biological agents to control the disease is important because no resistant cultivars or effective chemical fungicides are available. In this study, we tested the biological control capability of a chitinase produced by the endophytic bacterium Serratia proteamaculans 336x against wheat take-all. The chitinase gene chi1 of S. proteamaculans 336x was cloned and heterologously expressed in Escherichia coli. The recombinant protein exhibited chitinase activity and in vitro antifungal activity against G. graminis var. tritici. With in-frame deletion of the chi1 gene by homologous recombination, the chi1-deleted mutant was devoid of chitinase activity and the biocontrol efficacy was reduced by 42.5%. The complementation of the Δchi1 mutant strain by the chi1 gene resulted in the partial restoration of the chitinase activity and biocontrol efficacy. These results support a role for the Chi1 protein in the biocontrol process of S. proteamaculans 336x against wheat take-all.

Chitooligosaccharides are converted to N-acetylglucosamine by N-acetyl-β-hexosaminidase from Stenotrophomonas maltophilia

The Stenotrophomonas maltophilia k279a (Stm) Hex gene encodes a polypeptide of 785 amino acid residues, with an N-terminal signal peptide. StmHex was cloned without signal peptide and expressed as an 83.6 kDa soluble protein in Escherichia coli BL21 (DE3). Purified StmHex was optimally active at pH 5.0 and 40 °C. The Vmax, Km and kcat/Km for StmHex towards chitin hexamer were 10.55 nkat (mg protein)(-1), 271 μM and 0.246 s(-1) mM(-1), while the kinetic values with chitobiose were 30.65 nkat (mg protein)(-1), 2365 μM and 0.082 s(-1) mM(-1), respectively. Hydrolytic activity on chitooligosaccharides indicated that StmHex was an exo-acting enzyme and yielded N-acetyl-D-glucosamine (GlcNAc) as the final product. StmHex hydrolysed chitooligosaccharides (up to hexamer) into GlcNAc within 60 min, suggesting that this enzyme has potential for use in large-scale production of GlcNAc from chitooligosaccharides.

Potentiation of the synergistic activities of chitinases ChiA, ChiB and ChiC from Serratia marcescens CFFSUR-B2 by chitobiase (Chb) and chitin binding protein (CBP)

With the goal of understanding the chitinolytic mechanism of the potential biological control strain Serratia marcescens CFFSUR-B2, genes encoding chitinases ChiA, ChiB and ChiC, chitobiase (Chb) and chitin binding protein (CBP) were cloned, the protein products overexpressed in Escherichia coli as 6His-Sumo fusion proteins and purified by affinity chromatography. Following affinity tag removal, the chitinolytic activity of the recombinant proteins was evaluated individually and in combination using colloidal chitin as substrate. ChiB and ChiC were highly active while ChiA was inactive. Reactions containing both ChiB and ChiC showed significantly increased N-acetylglucosamine trimer and dimer formation, but decreased monomer formation, compared to reactions with either enzyme alone. This suggests that while both ChiB and ChiC have a general affinity for the same substrate, they attack different sites and together degrade chitin more efficiently than either enzyme separately. Chb and CBP in combination with ChiB and ChiC (individually or together) increased their chitinase activity. We report for the first time the potentiating effect of Chb on the activity of the chitinases and the synergistic activity of a mixture of all five proteins (the three chitinases, Chb and CBP). These results contribute to our understanding of the mechanism of action of the chitinases produced by strain CFFSUR-B2 and provide a molecular basis for its high potential as a biocontrol agent against fungal pathogens.

Chitinase A from Stenotrophomonas maltophilia shows transglycosylation and antifungal activities

Stenotrophomonas maltophilia chitinase (StmChiA and StmChiB) genes were cloned and expressed as soluble proteins of 70.5 and 41.6 kDa in Escherichia coli. Ni-NTA affinity purified StmChiA and StmChiB were optimally active at pH 5.0 and 7.0, respectively and exhibited broad range pH activity. StmChiA and StmChiB had an optimum temperature of 40°C and are stable up to 50 and 40°C, respectively. Hydrolytic activity on chitooligosaccharides indicated that StmChiA was an endo-acting enzyme releasing chitobiose and StmChiB was both exo/endo-acting enzyme with the release of GlcNAc as the final product. StmChiA showed higher preference to β-chitin and exhibited transglycosylation on even chain length tetra- and hexameric substrates. StmChiA, and not StmChiB, was active on chitinous polymers and showed antifungal activity against Fusarium oxysporum.

Bacterial chitin binding proteins show differential substrate binding and synergy with chitinases

Glycosyl hydrolase (GH) family 18 chitinases (Chi) and family 33 chitin binding proteins (CBPs) from Bacillus thuringiensis serovar kurstaki (BtChi and BtCBP), B. licheniformis DSM13 (BliChi and BliCBP) and Serratia proteamaculans 568 (SpChiB and SpCBP21) were used to study the efficiency and synergistic action of BtChi, BliChi and SpChiB individually with BtCBP, BliCBP or SpCBP21. Chitinase assay revealed that only BtChi and SpChiB showed synergism in hydrolysis of chitin, while there was no increase in products generated by BliChi, in the presence of the three above mentioned CBPs. This suggests that some (specific) CBPs are able to exert a synergistic effect on (specific) chitinases. A mutant of BliChi, designated as BliGH, was constructed by deleting the C-terminal fibronectin III (FnIII) and carbohydrate binding module 5 (CBM5) to assess the contribution of FnIII and CBM5 domains in the synergistic interactions of GH18 chitinases with CBPs. Chitinase assay with BliGH revealed that the accessory domains play a major role in making BliChi an efficient enzyme. We studied binding of BtCBP and BliCBP to α- and β-chitin. The BtCBP, BliCBP or SpCBP21 did not act synergistically with chitinases in hydrolysis of the chitin, interspersed with other polymers, present in fungal cell walls.

Transglycosylation by chitinase D from Serratia proteamaculans improved through altered substrate interactions

We describe the improvement of transglycosylation (TG) by chitinase D from Serratia proteamaculans (SpChiD). The SpChiD produced a smaller quantity of TG products for up to 90 min with 2 mm chitotetraose as the substrate and subsequently produced only hydrolytic products. Of the five residues targeted at the catalytic center, E159D resulted in substantial loss of both hydrolytic and TG activities. Y160A resulted in a product profile similar to SpChiD and a rapid turnover of substrate with slightly increased TG activity. The rest of the three mutants, M226A, Y228A, and R284A, displayed improved TG and decreased hydrolytic ability. Four of the five amino acid substitutions, F64W, F125A, G119S, and S116G, at the catalytic groove increased TG activity, whereas W120A completely lost the TG activity with a concomitant increase in hydrolysis. Mutation of Trp-247 at the solvent-accessible region significantly reduced the hydrolytic activity with increased TG activity. The mutants M226A, Y228A, F125A, S116G, F64W, G119S, R284A, and W247A accumulated approximately double the concentration of TG products like chitopentaose and chitohexaose, compared with SpChiD. The double mutant E159D/F64W regained the activity with accumulation of 6.0% chitopentaose at 6 h, similar to SpChiD at 30 min. Loss of chitobiase activity was unique to Y228A. Substitution of amino acids at the catalytic center and/or groove substantially improved the TG activity of SpChiD, both in terms of the quantity of TG products produced and the extended duration of TG activity.

Synthesis of long-chain chitooligosaccharides by a hypertransglycosylating processive endochitinase of Serratia proteamaculans 568

We describe the heterologous expression and characterization of a 407-residue single-domain glycosyl hydrolase family 18 chitinase (SpChiD) from Gram-negative Serratia proteamaculans 568 that has unprecedented catalytic properties. SpChiD was optimally active at pH 6.0 and 40 °C, where it showed a K(m) of 83 mg ml(-1), a k(cat) of 3.9 × 10(2) h(-1), and a k(cat)/K(m) of 4.7 h mg(-1) ml(-1) on colloidal chitin. On chitobiose, the K(m), k(cat), and k(cat)/K(m) were 203 μM, 1.3 × 10(2) h(-1), and 0.62 h(-1) μM(-1), respectively. Hydrolytic activity on chitooligosaccharides (CHOS) and colloidal chitin indicated that SpChiD was an endo-acting processive enzyme, with the unique ability to convert released chitobiose to N-acetylglucosamine, the major end product. SpChiD showed hyper transglycosylation (TG) with trimer-hexamer CHOS substrates, generating considerable amounts of long-chain CHOS. The TG activity of SpChiD was dependent on both the length and concentration of the oligomeric substrate and also on the enzyme concentration. The length and amount of accumulated TG products increased with increases in the length of the substrate and its concentration and decreased with increases in the enzyme concentration. The SpChiD bound to insoluble and soluble chitin substrates despite the absence of accessory domains. Sequence alignments and structural modeling indicated that SpChiD would have a deep substrate-binding groove lined with aromatic residues, which is characteristic of processive enzymes. SpChiD shows a combination of properties that seems rare among family 18 chitinases and that may resemble the properties of human chitotriosidase.

Chitin binding proteins act synergistically with chitinases in Serratia proteamaculans 568

Genome sequence of Serratia proteamaculans 568 revealed the presence of three family 33 chitin binding proteins (CBPs). The three Sp CBPs (Sp CBP21, Sp CBP28 and Sp CBP50) were heterologously expressed and purified. Sp CBP21 and Sp CBP50 showed binding preference to β-chitin, while Sp CBP28 did not bind to chitin and cellulose substrates. Both Sp CBP21 and Sp CBP50 were synergistic with four chitinases from S. proteamaculans 568 (Sp ChiA, Sp ChiB, Sp ChiC and Sp ChiD) in degradation of α- and β-chitin, especially in the presence of external electron donor (reduced glutathione). Sp ChiD benefited most from Sp CBP21 or Sp CBP50 on α-chitin, while Sp ChiB and Sp ChiD had major advantage with these Sp CBPs on β-chitin. Dose responsive studies indicated that both the Sp CBPs exhibit synergism ≥0.2 µM. The addition of both Sp CBP21 and Sp CBP50 in different ratios to a synergistic mixture did not significantly increase the activity. Highly conserved polar residues, important in binding and activity of CBP21 from S. marcescens (Sm CBP21), were present in Sp CBP21 and Sp CBP50, while Sp CBP28 had only one such polar residue. The inability of Sp CBP28 to bind to the test substrates could be attributed to the absence of important polar residues.