Recombinant expression of chitosanase from Bacillus subtilis HD145 in Pichia pastoris

Expression of chitosanase from Aspergillus fumigatus chitosanase in Saccharomyces cerevisiae by CRISPR-Cas9 tools

Chitooligosaccharides (COS) find numerous applications due to their exceptional properties. Enzymatic hydrolysis of chitosan by chitosanase is considered an advantageous route for COS production. Heterologous expression of chitosanase holds significant promise, yet studies using commonly employed Escherichia coli and Pichia pastoris strains encounter challenges in subsequent handling and industrial scalability. In this investigation, we opted for using the safe yeast strain Saccharomyces cerevisiae (GRAS), obviating the need for methanol induction, resulting in successful expression. Ultimately, utilizing the GTR-CRISPR editing system, shake flask enzyme activity reached 2 U/ml. The optimal chitosanase activity was achieved at 55℃ and pH 5, with favorable stability between 30 and 50 °C. Following a 2-h catalytic reaction, the product primarily consisted of chitobiose to chitotetraose, predominantly at the chitotriose position, with a slight increase in chitobiose content observed during the later stages of enzymatic hydrolysis. The results affirm the feasibility of heterologous chitosanase expression through Saccharomyces cerevisiae, underscoring its significant industrial potential.

Secretory production and characterization of a highly effective chitosanase from Streptomyces coelicolor A3(2) M145 in Pichia pastoris

In this study, a glycoside hydrolase family 46 chitosanase from Streptomyces coelicolor A3(2) M145 was firstly cloned and expressed in Pichia pastoris GS115 (P. pastoris GS115). The recombinant enzyme (CsnA) showed maximal activity at pH 6.0 and 65°C. Both thermal stability and pH stability of CsnA expressed in P. pastoris GS115 were significantly increased compared with homologous expression in Streptomyces coelicolor A3(2). A stable chitosanase activity of 725.7 ± 9.58 U mL-1 was obtained in fed-batch fermentation. It's the highest level of CsnA from Streptomyces coelicolor expressed in P. pastoris so far. The hydrolytic process of CsnA showed a time-dependent manner. Chitosan oligosaccharides (COSs) generated by CsnA showed antifungal activity against Fusarium oxysporum sp. cucumerinum (F. oxysporum sp. cucumerinum). The secreted expression and hydrolytic performance make the enzyme a desirable biocatalyst for industrial controllable production of chitooligosaccharides with specific degree of polymerization, which have potential to control fungi that cause important crop diseases.

Enhancing the thermostability and catalytic activity of Bacillus subtilis chitosanase by saturation mutagenesis of Lys242

Catalysis activity and thermostability are some of the fundamental characteristic of enzymes, which are of great significance to their industrial applications. Bacillus subtilis chitosanase BsCsn46A is a kind of enzyme with good catalytic activity and stability, which can hydrolyze chitosan to produce chitobiose and chitotriose. In order to further improve the catalytic activity and stability of BsCsn46A, saturation mutagenesis of the C-terminal K242 of BsCsn46A was performed. The results showed that the six mutants (K242A, K242D, K242E, K242F, K242P, and K242T) showed increased catalytic activity on chitosan. The catalytic activity of K242P increased from 12971 ± 597 U mg-1 of wild type to 17820 ± 344 U mg-1 , and the thermostability of K242P increased by 2.27%. In order to elucidate the reason for the change of enzymatic properties, hydrogen network, molecular docking, and molecular dynamics simulation were carried out. The hydrogen network results showed that all the mutants lose their interaction with Asp6 at 242 site, thereby increasing the flexibility of Glu19 at the junction sites of α1 and loop1. Molecular dynamics results showed that the RMSD of K242P was lower at both 313 and 323 K than that of other mutants, which supported that K242P had better thermostability. The catalytic activity of mutant K242P reached 17820.27 U mg-1 , the highest level reported so far, which could be a robust candidate for the industrial application of chitooligosaccharide (COS) production.

Structure-based mining of a chitosanase with distinctive degradation mode and product specificity

Chitosan derivates with varying degrees of polymerization (DP) have attracted great concern due to their excellent biological activities. Increasing the abundance of chitosanases with different degradation modes contributes to revealing their catalytic mechanisms and facilitating the production of chitosan derivates. However, the identification of endo-chitosanases capable of producing chitobiose and D-glucosamine (GlcN) from chitosan substrates has remained elusive. Herein, an endo-chitosanase (CsnCA) belonging to the GH46 family was identified based on structural analysis in phylogenetic evolution. Moreover, we demonstrate that CsnCA acts in a random endo-acting manner, producing chitosan derivatives with DP ≤ 2. The in-depth analysis of CsnCA revealed that (GlcN)3 serves as the minimal substrate, undergoing cleavage in the mode that occupies the subsites - 2 to + 1, resulting in the release of GlcN. This study succeeded in discovering a chitosanase with distinctive degradation modes, which could facilitate the mechanistic understanding of chitosanases, further empowering the production of chitosan derivates with specific DP. KEY POINTS: • Structural docking and evolutionary analysis guide to mining the chitosanase. • The endo-chitosanase exhibits a unique GlcN-producing cleavage pattern. • The cleavage direction of chitosanase to produce GlcN was identified.

Rational Redesign of Chitosanase to Enhance Thermostability and Catalytic Activity to Produce Chitooligosaccharides with a Relatively High Degree of Polymerization

Chitooligosaccharides (hdpCOS) with a high degree of polymerization (hdp, DP 4-10) generally have greater biological activities than those of low-DP (ldp, DP 2-3) COS. Chitosanase from Bacillus amyloliquefaciens KCP2 (Csn46) can degrade chitosan to more hdpCOS at high temperature (70 °C), but low thermal stability at this temperature makes it unsuitable for industrial application; the wild-type enzyme can only produce COS (DP 2-4) at lower temperatures. Several thermostable mutants were obtained by modifying chitosanase using a comprehensive strategy based on a computer-aided mutant design. A combination of four beneficial single-point mutations (A129L/T175 V/K70T/D34G) to Csn46 was selected to obtain a markedly improved mutant, Mut4, with a half-life at 60 °C extended from 34.31 to 690.80 min, and the specific activity increased from 1671.73 to 3528.77 U/mg. Mut4 produced COS with DPs of 2-4 and 2-7 at 60 and 70 °C, respectively. Therefore, Mut4 has the potential to be applied to the industrial-scale preparation of hdpCOS with high biological activity.

Production, Characterization and Application of a Novel Chitosanase from Marine Bacterium Bacillus paramycoides BP-N07

Chitooligosaccharides (COS), a high-value chitosan derivative, have many applications in food, pharmaceuticals, cosmetics and agriculture owing to their unique biological activities. Chitosanase, which catalyzes the hydrolysis of chitosan, can cleave β-1,4 linkages to produce COS. In this study, a chitosanase-producing Bacillus paramycoides BP-N07 was isolated from marine mud samples. The chitosanase enzyme (BpCSN) activity was 2648.66 ± 20.45 U/mL at 52 h and was able to effectively degrade chitosan. The molecular weight of purified BpCSN was approximately 37 kDa. The yield and enzyme activity of BpCSN were 0.41 mg/mL and 8133.17 ± 47.83 U/mg, respectively. The optimum temperature and pH of BpCSN were 50 °C and 6.0, respectively. The results of the high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) of chitosan treated with BpCSN for 3 h showed that it is an endo-chitosanase, and the main degradation products were chitobiose, chitotriose and chitotetraose. BpCSN was used for the preparation of oligosaccharides: 1.0 mg enzyme converted 10.0 g chitosan with 2% acetic acid into oligosaccharides in 3 h at 50 °C. In summary, this paper reports that BpCSN has wide adaptability to temperature and pH and high activity for hydrolyzing chitosan substrates. Thus, BpCSN is a chitosan decomposer that can be used for producing chitooligosaccharides industrially.

A Novel Cold-Adapted and High-Alkaline Alginate Lyase with Potential for Alginate Oligosaccharides Preparation

Alginate oligosaccharides (AOs) prepared through enzymatic reaction by diverse alginate lyases under relatively controllable and moderate conditions possess versatile biological activities. But widely used commercial alginate lyases are still rather rare due to their poor properties (e.g., lower activity, worse thermostability, ion tolerance, etc.). In this work, the alginate lyase Alyw208, derived from Vibrio sp. W2, was expressed in Yarrowia lipolytica of food grade and characterized in order to obtain an enzyme with excellent properties adapted to industrial requirements. Alyw208 classified into the polysaccharide lyase (PL) 7 family showed maximum activity at 35 °C and pH 10.0, indicating its cold-adapted and high-alkaline properties. Furthermore, Alyw208 preserved over 70% of the relative activity within the range of 10-55 °C, with a broader temperature range for the activity compared to other alginate-degrading enzymes with cold adaptation. Recombinant Alyw208 was significantly activated with 1.5 M NaCl to around 2.1 times relative activity. In addition, the endolytic Alyw208 was polyG-preferred, but identified as a bifunctional alginate lyase that could degrade both polyM and polyG effectively, releasing AOs with degrees of polymerization (DPs) of 2-6 and alginate monomers as the final products (that is, DPs 1-6). Alyw208 has been suggested with favorable properties to be a potent candidate for biotechnological and industrial applications.

Enhancing Enzyme Activity and Thermostability of Bacillus amyloliquefaciens Chitosanase BaCsn46A Through Saturation Mutagenesis at Ser196

Chitosanase plays an important role in chitooligosaccharides (COS) production. We found that the chitosanase (BaCsn46A) of Bacillus amyloliquefacien was a good candidate for chitosan hydrolysis of COS. In order to further improve the enzyme properties of BaCsn46A, the S196 located near the active center was found to be a critical site impacts on enzyme properties by sequence alignment analysis. Herein, saturation mutation was carried out to study role of 196 site on BaCsn46A catalytic function. Compared with WT, the specific enzyme activity of S196A increased by 118.79%, and the thermostability of S196A was much higher than WT. In addition, we found that the enzyme activity of S196P was 2.41% of that of WT, indicating that the type of amino acid in 196 site could significant affect the catalytic activity and thermostability of BaCsn46A. After molecular docking analysis we found that the increase in hydrogen bonds and decrease in unfavorable bonds interacting with the substrate were the main reason for the change of enzyme properties which is valuable for future studies on Bacillus species chitosanase.

Molecular characterization of a novel strain of Bacillus halotolerans protecting wheat from sheath blight disease caused by Rhizoctonia solani Kühn

Rhizoctonia solani Kühn naturally infects and causes Sheath blight disease in cereal crops such as wheat, rice and maize, leading to severe reduction in grain yield and quality. In this work, a new bacterial strain Bacillus halotolerans LDFZ001 showing efficient antagonistic activity against the pathogenic strain Rhizoctonia solani Kühn sh-1 was isolated. Antagonistic, phylogenetic and whole genome sequencing analyses demonstrate that Bacillus halotolerans LDFZ001 strongly suppressed the growth of Rhizoctonia solani Kühn sh-1, showed a close evolutionary relationship with B. halotolerans F41-3, and possessed a 3,965,118 bp circular chromosome. Bioinformatic analysis demonstrated that the genome of Bacillus halotolerans LDFZ001 contained ten secondary metabolite biosynthetic gene clusters (BGCs) encoding five non-ribosomal peptide synthases, two polyketide synthase, two terpene synthases and one bacteriocin synthase, and a new kijanimicin biosynthetic gene cluster which might be responsible for the biosynthesis of novel compounds. Gene-editing experiments revealed that functional expression of phosphopantetheinyl transferase (SFP) and major facilitator superfamily (MFS) transporter genes in Bacillus halotolerans LDFZ001 was essential for its antifungal activity against R. solani Kühn sh-1. Moreover, the existence of two identical chitosanases may also make contribution to the antipathogen activity of Bacillus halotolerans LDFZ001. Our findings will provide fundamental information for the identification and isolation of new sheath blight resistant genes and bacterial strains which have a great potential to be used for the production of bacterial control agents.

IMPORTANCE

A new Bacillus halotolerans strain Bacillus halotolerans LDFZ001 resistant to sheath blight in wheat is isolated. Bacillus halotolerans LDFZ001 harbors a new kijanimicin biosynthetic gene cluster, and the functional expression of SFP and MFS contribute to its antipathogen ability.

Heterologous Expression of GH5 Chitosanase in Pichia pastoris and Antioxidant Biological Activity of Its Chitooligosacchride Hydrolysate

Chitosanase was widely used in the production of bioactive chitooligosacchride (CHOS) due to their safety, controllability, environmental protection, and biodegradability. Studies showed that the bioactivity of CHOS is closely related to its degree of polymerization. Therefore, the production of ideal polymerized CHOS becomes our primary goal. In this study, the glycosyl hydrolase (GH) family 5 chitosanase was successfully expressed heterologously in Pichia pastoris. After 96h of high-density fermentation, the chitosanase activity reached 90.62 U·mL^-1, the protein content reached 9.76mg·mL^-1. When 2% chitosan was hydrolyzed by crude enzyme (20U/mL), the hydrolysis rate reached 91.2% after 8h, producing a mixture of CHOS with 2-4 desirable degrees of polymerization (DP). Then, the antioxidant activity of CHOS mixture was investigated, and the results showed that the antioxidant effect was concentration-dependent and had great application potential in the field of nutrition.

A temperature-induced chitosanase bacterial cell-surface display system for the efficient production of chitooligosaccharides

OBJECTIVE

To establish a temperature-induced chitosanase bacterial cell-surface display system to produce chitooligosaccharides (COSs) efficiently for industrial applications.

RESULTS

Temperature-inducible chitosanase CSN46A bacterial surface display systems containing one or two copies of ice nucleation protein (InaQ-N) as anchoring motifs were successfully constructed on the basis of Escherichia coli and named as InaQ-N-CSN46A (1 copy) and 2InaQ-N-CSN46A (2 copies). The specific enzyme activity of 2InaQ-N-CSN46A reached 761.34 ± 0.78 U/g cell dry weight, which was 45.6% higher than that of InaQ-N-CSN46A. However, few proteins were detected in the 2InaQ-N-CSN46A hydrolysis system. Therefore, 2InaQ-N-CSN46A had higher hydrolysis efficiency and stability than InaQ-N-CSN46A. Gel permeation chromatography revealed that under the optimum enzymatic hydrolysis temperature, the final products were mainly chitobiose and chitotriose. Chitopentaose accumulated (77.62%) when the hydrolysis temperature reached 60 °C. FTIR and NMR analysis demonstrated that the structures of the two hydrolysis products were consistent with those of COSs.

CONCLUSIONS

In this study, chitosanase was expressed on the surfaces of E. coli by increasing the induction temperature, and chitosan was hydrolysed directly without enzyme purification steps. This study provides a novel strategy for industrial COS production.

Biochemical characterization of a novel bifunctional chitosanase from Paenibacillus barengoltzii for chitooligosaccharide production

A novel chitosanase gene, designated as PbCsn8, was cloned from Paenibacillus barengoltzii. It shared the highest identity of 73% with the glycoside hydrolase (GH) family 8 chitosanase from Bacillus thuringiensis JAM-GG01. The gene was heterologously expressed in Bacillus subtilis as an extracellular protein, and the highest chitosanase yield of 1, 108 U/mL was obtained by high-cell density fermentation in a 5-L fermentor. The recombinant chitosanase (PbCsn8) was purified to homogeneity and biochemically characterized. PbCsn8 was most active at pH 5.5 and 70 °C, respectively. It was stable in a wide pH range of 5.0-11.0 and up to 55 °C. PbCsn8 was a bifunctional enzyme, exhibiting both chitosanase and glucanase activities, with the highest specificity towards chitosan (360 U/mg), followed by barley β-glucan (72 U/mg) and lichenan (13 U/mg). It hydrolyzed chitosan to release mainly chitooligosaccharides (COSs) with degree of polymerization (DP) 2-3, while hydrolyzed barley β-glucan to yield mainly glucooligosaccharides with DP > 5. PbCsn8 was further applied in COS production, and the highest COS yield of 79.3% (w/w) was obtained. This is the first report on a GH family 8 chitosanase from P. barengoltzii. The high yield and remarkable hydrolysis properties may make PbCsn8 a good candidate in industrial application.

Preparation of Active Chitooligosaccharides with a Novel Chitosanase AqCoA and Their Application in Fungal Disease Protection

Enzymes that degrade fungal cell walls and the resulting oligosaccharides are promising weapons to combat plant fungal disease. In this study, we identified a novel endo-chitosanase, AqCoA, from Aquabacterium sp. A7-Y. The enzyme showed a specific activity of 18 U/mg toward 95% deacetylated chitosan at pH 5.0 and 40 °C. AqCoA also showed activity toward sodium carboxymethylcellulose, indicating substrate promiscuity. AqCoA hydrolyzed chitosan into chitooligosaccharides (CoA-COSs) with degrees of polymerization (DPs) of 3-5 but showed no activity toward CoA-COSs with DPs <6, indicating an endo-type activity. At 2.5 μg/mL, AqCoA inhibited appressorium formation of Magnaporthe oryzae; the produced CoA-COSs also inhibited the growth of M. oryzae and Fusarium oxysporum. Furthermore, CoA-COSs acted as immune elicitors in rice by inducing the reactive oxygen species burst and the expression of defense genes. These results demonstrated that AqCoA and its resulting CoA-COSs might be effective tools for protecting plants against pathogenic fungi.

Marine-polysaccharide degrading enzymes: Status and prospects

Marine-polysaccharide degrading enzymes have recently been studied extensively. They are particularly interesting as they catalyze the cleavage of glycosidic bonds in polysaccharide macromolecules and produce oligosaccharides with low degrees of polymerization. Numerous findings have demonstrated that marine polysaccharides and their biotransformed products possess beneficial properties including antitumor, antiviral, anticoagulant, and anti-inflammatory activities, and they have great value in healthcare, cosmetics, the food industry, and agriculture. Exploitation of enzymes that can degrade marine polysaccharides is in the ascendant, and is important for high-value use of marine biomass resources. In this review, we describe research and prospects regarding the classification, biochemical properties, and catalytic mechanisms of the main types of marine-polysaccharide degrading enzymes, focusing on chitinase, chitosanase, alginate lyase, agarase, and carrageenase, and their product oligosaccharides. The state-of-the-art discussion of marine-polysaccharide degrading enzymes and their properties offers information that might enable more efficient production of marine oligosaccharides. We also highlight current problems in the field of marine-polysaccharide degrading enzymes and trends in their development. Understanding the properties, catalytic mechanisms, and modification of known enzymes will aid the identification of novel enzymes to degrade marine polysaccharides and facilitation of their use in various biotechnological processes.

High level production of a Bacillus amlyoliquefaciens chitosanase in Pichia pastoris suitable for chitooligosaccharides preparation

Chitooligosaccharides (COS) are hydrolytic products of chitosan that are essential in functional food, medicine, and other fields due to their biological activities. Commercial COS are often prepared by the hydrolysis of chitosan by chitosanase. In this study, a glycoside hydrolase family 46 cluster B chitosanase from Bacillus amyloliquefaciens (BaCsn46B) was efficiently expressed in Pichia pastoris. The recombinant enzyme was secreted into the culture medium that reached a total extracellular protein concentration of 4.5 g/L with an activity of 8907.2 U/mL in a high cell density fermenter (5 L). The molecular mass of deglycosylated BaCsn46B was 29.0 kDa. Purified BaCsn46B exhibited excellent enzymatic properties, which had high specific activity (2380.5 U/mg) under optimal reaction conditions (55 °C and pH 6.5). BaCsn46B hydrolyzed chitosan yielded a series of COS with different degrees of polymerization by endo-type cleavage. The end hydrolytic products of BaCsn46B were chitobiose and chitotriose, while no monosaccharide yield was evident in the hydrolytic reaction. The excellent secreted expression level and hydrolytic performance make the enzyme a desirable biocatalyst for the industrial preparation of COS.

Purification of Recombinant Glycoproteins from Pichia pastoris Culture Supernatants

Pichia pastoris is a common host organism for the production of recombinant proteins. While unglycosylated recombinant proteins derived from this yeast can be purified efficiently by only a few conventional chromatography steps, the purification of glycosylated recombinant proteins is a very challenging process due to the intrinsic feature of the yeast of hypermannosylation. The resulting vast glycosylation pattern on the recombinant target protein masks its physicochemical properties hampering a conventional downstream process. Here, we describe a fast and efficient two-step chromatography strategy, where both steps are operated in flow-through mode, to purify recombinant glycoproteins from P. pastoris culture supernatants.

High-Level Expression of a Thermally Stable Alginate Lyase Using Pichia pastoris, Characterization and Application in Producing Brown Alginate Oligosaccharide

An alginate lyase encoding gene sagl from Flavobacterium sp. H63 was codon optimized and recombinantly expressed at high level in P.pastoris through high cell-density fermentation. The highest yield of recombinant enzyme of sagl (rSAGL) in yeast culture supernatant reached 226.4 μg/mL (915.5 U/mL). This was the highest yield record of recombinant expression of alginate lyase so far. The rSAGL was confirmed as a partially glycosylated protein through EndoH digestion. The optimal reaction temperature and pH of this enzyme were 45 °C and 7.5; 80 mM K⁺ ions could improve the catalytic activity of the enzyme by 244% at most. rSAGL was a thermal stable enzyme with T50¹⁵ of 57⁻58 °C and T50³⁰ of 53⁻54 °C. Its thermal stability was better than any known alginate lyase. In 100 mM phosphate buffer of pH 6.0, rSAGL could retain 98.8% of the initial activity after incubation at 50 °C for 2 h. Furthermore, it could retain 61.6% of the initial activity after 48 h. The specific activity of the purified rSAGL produced by P. pastoris attained 4044 U/mg protein, which was the second highest record of alginate lyase so far. When the crude enzyme of the rSAGL was directly used in transformation of sodium alginate with 40 g/L, 97.2% of the substrate was transformed to di, tri, tetra brown alginate oligosaccharide after 32 h of incubation at 50 °C, and the final concentration of reducing sugar in mixture reached 9.51 g/L. This is the first report of high-level expression of thermally stable alginate lyase using P. pastoris system.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Recent Progress in Chitosanase Production of Monomer-Free Chitooligosaccharides: Bioprocess Strategies and Future Applications

Biological activities of chitosan oligosaccharides (COS) are well documented, and numerous reports of COS production using specific and non-specific enzymes are available. However, strategies for improving the overall yield by making it monomer free need to be developed. Continuous enzymatic production from chitosan derived from marine wastes is desirable and is cost-effective. Isolation of potential microbes showing chitosanase activity from various ecological niches, gene cloning, enzyme immobilization, and fractionation/purification of COS are some areas, where lot of work is in progress. This review covers recent measures to improve monomer-free COS production using chitosanase/non-specific enzymes and purification/fractionation of these molecules using ultrafiltration and column chromatographic techniques. Various bioprocess strategies, gene cloning for enhanced chitosanase enzyme production, and other measures for COS yield improvements have also been covered in this review. COS derivative preparation as well as COS-coated nanoparticles for efficient drug delivery are being focused in recent studies.

Glyco-variant library of the versatile enzyme horseradish peroxidase

When the glycosylated plant enzyme horseradish peroxidase (HRP) is conjugated to specific antibodies, it presents a powerful tool for medical applications. The isolation and purification of this enzyme from plant is difficult and only gives low yields. However, HRP recombinantly produced in the yeast Pichia pastoris experiences hyperglycosylation, which impedes the use of this enzyme in medicine. Enzymatic and chemical deglycosylation are cost intensive and cumbersome and hitherto existing P. pastoris strain engineering approaches with the goal to avoid hyperglycosylation only resulted in physiologically impaired yeast strains not useful for protein production processes. Thus, the last resort to obtain less glycosylated recombinant HRP from P. pastoris is to engineer the enzyme itself. In the present study, we mutated all the eight N-glycosylation sites of HRP C1A. After determination of the most suitable mutation at each N-glycosylation site, we physiologically characterized the respective P. pastoris strains in the bioreactor and purified the produced HRP C1A glyco-variants. The biochemical characterization of the enzyme variants revealed great differences in catalytic activity and stability and allowed the combination of the most promising mutations to potentially give an unglycosylated, active HRP C1A variant useful for medical applications. Interestingly, site-directed mutagenesis proved to be a valuable strategy not only to reduce the overall glycan content of the recombinant enzyme but also to improve catalytic activity and stability. In the present study, we performed an integrated bioprocess covering strain generation, bioreactor cultivations, downstream processing and product characterization and present the biochemical data of the HRP glyco-library.

Recent developments in chitosanase research and its biotechnological applications: a review

Chitosanases (EC 3.2.1.132) are glycosyl hydrolases that catalyse the endohydrolysis of β-1,4-glycosidic bonds of partially acetylated chitosan to release chitosan oligosaccharides (COS). Chitosanases are isolated, purified and characterised from different sources mainly from bacteria and fungi. Chitosanases have received much attention due to their wide range of applications including the preparation of bioactive COS and fungal protoplasts, as biocontrol agent against pathogenic fungi and insects, the bioconversion of chitinous bio waste associated with seafood processing, etc. Bioactive COS produced by the enzymatic hydrolysis of chitosan have finds numerous health benefits as well as other biological activities. This review summarizes the recent advances in chitosanases research, the enzyme production processes, characterization, genetic improvement and their applications.

Production of recombinant Bacillus subtilis chitosanase, suitable for biosynthesis of chitosan-oligosaccharides

Chitosanases are enzymes that catalyse the hydrolysis of the β-1,4 glycosidic bond of chitosan. One of the most promising applications of this enzyme is for the bioconversion of chitosan into value-added chitosan-oligosaccharides (COS). GH46 chitosanase (Csn) from Bacillus subtilis 168 was expressed in Escherichia coli by fusing the gene encoding mature Csn to the E. coli OmpA signal peptide sequence. The recombinant enzyme was secreted into the culture supernatant. The recombinant Csn showed high specific activity and stability over a wide range of pH. The enzyme was >100 times more thermostable in the presence of the substrate, with a half-life time of activity (τ(1/2)) of approximately 20 h at 50 °C and pH 5.5. Efficient bioconversion of chitosan into different mixtures of COS, using crude culture supernatant containing secreted enzyme was demonstrated.