Degradation of chitosans with chitinase B from Serratia marcescens

Validated HPAEC-PAD Method for the Determination of Fully Deacetylated Chitooligosaccharides

An efficient and sensitive analytical method based on high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was established for the simultaneous separation and determination of glucosamine (GlcN)₁ and chitooligosaccharides (COS) ranging from (GlcN)₂ to (GlcN)₆ without prior derivatization. Detection limits were 0.003 to 0.016 mg/L (corresponding to 0.4-0.6 pmol), and the linear range was 0.2 to 10 mg/L. The optimized analysis was carried out on a CarboPac-PA100 analytical column (4 × 250 mm) using isocratic elution with 0.2 M aqueous sodium hydroxide-water mixture (10:90, v/v) as the mobile phase at a 0.4 mL/min flow rate. Regression equations revealed a good linear relationship (R² = 0.9979-0.9995, n = 7) within the test ranges. Quality parameters, including precision and accuracy, were fully validated and found to be satisfactory. The fully validated HPAEC-PAD method was readily applied for the quantification of (GlcN)_1-6 in a commercial COS technical concentrate. The established method was also used to monitor the acid hydrolysis of a COS technical concentrate to ensure optimization of reaction conditions and minimization of (GlcN)₁ degradation.

A novel analytical method for d-glucosamine quantification and its application in the analysis of chitosan degradation by a minimal enzyme cocktail

Enzymatic depolymerization of chitosan, a β-(1,4)-linked polycationic polysaccharide composed of d-glucosamine (GlcN) and N-acetyl-d-glucosamine (GlcNAc) provides a possible route to the exploitation of chitin-rich biomass. Complete conversion of chitosan to mono-sugars requires the synergistic action of endo- and exo- chitosanases. In the present study we have developed an efficient and cost-effective chitosan-degrading enzyme cocktail containing only two enzymes, an endo-attacking bacterial chitosanase, ScCsn46A, from Streptomyces coelicolor, and an exo-attacking glucosamine specific β-glucosaminidase, Tk-Glm, from the archaeon Thermococcus kodakarensis KOD1. Moreover, we developed a fast, reliable quantitative method for analysis of GlcN using high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The sensitivity of this method is high and less than 50 pmol was easily detected, which is about 1000-fold better than the sensitivity of more commonly used detection methods based on refractive index. We also obtained qualitative insight into product development during the enzymatic degradation reaction by means of ElectroSpray Ionization-Mass Spectrometry (ESI-MS).

Preparation of chitooligosaccharides from fungal waste mycelium by recombinant chitinase

This study aimed to develop an enzymatic method for conversion of chitin from fungal waste mycelia to chitooligosaccharides. The recombinant chitinase LlChi18A from Lactococcus lactis was over-expressed by Escherichia coli BL21 (DE3) and purified by affinity chromatography. The enzymatic properties of the purified enzyme were studied by chitin oligosaccharides. Waste mycelium was pre-treated by alkaline. The optimal conditions for hydrolysis of fungal chitin by recombinant chitinase were determined by Schales method. HPLC/ESI-MS was used to determine the content of N-acetylglucosamine and chitooligosaccharides after hydrolysis. The level of reducing sugar released from pretreated mycelium by chitinase increased with the reaction time during 6 days. The main product in the hydrolysates was N,N'-diacetylchitobiose. After hydrolysis by chitinase for 5 d, the yield of N,N'-diacetylchitobiose from waste mycelium was around 10% with estimated purity of around 70%. Combination of chitinase and snailase remarkably increased the yield to 24% with purity of 78%. Fungal mycelium which contains chitin is a new potential source for obtaining food grade chitooligosaccharides.

Processivity, Substrate Positioning, and Binding: The Role of Polar Residues in a Family 18 Glycoside Hydrolase

The enzymatic degradation of recalcitrant polysaccharides such as cellulose (β-1,4-linked glucose) and chitin (β-1,4-linked N-acetylglucosamine) by glycoside hydrolases (GHs) is of significant biological and economical importance. In nature, depolymerization is primarily accomplished by processive GHs, which remain attached to the substrate between subsequent hydrolytic reactions. Recent computational efforts have suggested that the processive ability of a GH is directly linked to the ligand binding free energy. The contribution of individual aromatic residues in the active site of these enzymes has been extensively studied. In this study, we offer the first experimental evidence confirming correlation of binding free energy and degree of processivity and evidence that polar residues are essential for maintaining processive ability. Exchanging Thr(276) with Ala in substrate binding subsite -2 in the processive ChiA of Serratia marcescens results in a decrease in both the enthalpy (2.6 and 3.8 kcal/mol) and free energy (0.5 and 2.2 kcal/mol) for the binding to the substrate (GlcNAc)6 and the inhibitor allosamidin, respectively, compared to that of the wild type. Moreover, the initial apparent processivity as measured by [(GlcNAc)2]/[GlcNAc] ratios (17.1 ± 0.4) and chitin degradation efficiency (20%) are greatly reduced for ChiA-T276A versus those of the wild type (30.1 ± 1.5 and 75%, respectively). Mutation of Arg(172) to Ala reduces the level of recognition and positioning of the substrate into the active site. Molecular dynamics simulations indicate ChiA-R172A behaves like the wild type, but the dynamics of ChiA-T276A are greatly influenced by mutation, which is reflective of their influence on processivity.

Enzymatic production of defined chitosan oligomers with a specific pattern of acetylation using a combination of chitin oligosaccharide deacetylases

Chitin and chitosan oligomers have diverse biological activities with potentially valuable applications in fields like medicine, cosmetics, or agriculture. These properties may depend not only on the degrees of polymerization and acetylation, but also on a specific pattern of acetylation (PA) that cannot be controlled when the oligomers are produced by chemical hydrolysis. To determine the influence of the PA on the biological activities, defined chitosan oligomers in sufficient amounts are needed. Chitosan oligomers with specific PA can be produced by enzymatic deacetylation of chitin oligomers, but the diversity is limited by the low number of chitin deacetylases available. We have produced specific chitosan oligomers which are deacetylated at the first two units starting from the non-reducing end by the combined use of two different chitin deacetylases, namely NodB from Rhizobium sp. GRH2 that deacetylates the first unit and COD from Vibrio cholerae that deacetylates the second unit starting from the non-reducing end. Both chitin deacetylases accept the product of each other resulting in production of chitosan oligomers with a novel and defined PA. When extended to further chitin deacetylases, this approach has the potential to yield a large range of novel chitosan oligomers with a fully defined architecture.

Bioproduction of chitooligosaccharides: present and perspectives

Chitin and chitosan oligosaccharides (COS) have been traditionally obtained by chemical digestion with strong acids. In light of the difficulties associated with these traditional production processes, environmentally compatible and reproducible production alternatives are desirable. Unlike chemical digestion, biodegradation of chitin and chitosan by enzymes or microorganisms does not require the use of toxic chemicals or excessive amounts of wastewater. Enzyme preparations with chitinase, chitosanase, and lysozymeare primarily used to hydrolyze chitin and chitosan. Commercial preparations of cellulase, protease, lipase, and pepsin provide another opportunity for oligosaccharide production. In addition to their hydrolytic activities, the transglycosylation activity of chitinolytic enzymes might be exploited for the synthesis of desired chitin oligomers and their derivatives. Chitin deacetylase is also potentially useful for the preparation of oligosaccharides. Recently, direct production of oligosaccharides from chitin and crab shells by a combination of mechanochemical grinding and enzymatic hydrolysis has been reported. Together with these, other emerging technologies such as direct degradation of chitin from crustacean shells and microbial cell walls, enzymatic synthesis of COS from small building blocks, and protein engineering technology for chitin-related enzymes have been discussed as the most significant challenge for industrial application.

Bioproduction of chitooligosaccharides: present and perspectives

Chitin and chitosan oligosaccharides (COS) have been traditionally obtained by chemical digestion with strong acids. In light of the difficulties associated with these traditional production processes, environmentally compatible and reproducible production alternatives are desirable. Unlike chemical digestion, biodegradation of chitin and chitosan by enzymes or microorganisms does not require the use of toxic chemicals or excessive amounts of wastewater. Enzyme preparations with chitinase, chitosanase, and lysozymeare primarily used to hydrolyze chitin and chitosan. Commercial preparations of cellulase, protease, lipase, and pepsin provide another opportunity for oligosaccharide production. In addition to their hydrolytic activities, the transglycosylation activity of chitinolytic enzymes might be exploited for the synthesis of desired chitin oligomers and their derivatives. Chitin deacetylase is also potentially useful for the preparation of oligosaccharides. Recently, direct production of oligosaccharides from chitin and crab shells by a combination of mechanochemical grinding and enzymatic hydrolysis has been reported. Together with these, other emerging technologies such as direct degradation of chitin from crustacean shells and microbial cell walls, enzymatic synthesis of COS from small building blocks, and protein engineering technology for chitin-related enzymes have been discussed as the most significant challenge for industrial application.

Structural insights into the substrate-binding mechanism for a novel chitosanase

We present the first chitosanase–substrate complex structure, and, in combination with a mutagenesis and thermal stability assay, we elucidate the chitosanase–substrate binding mechanism precisely for the first time. The structural basis for chitosanase cleavage specificity is analysed as well.

Chitosan-Soyprotein Interaction as Determined by Thermal Unfolding Experiments

Chitosan interaction with soybean beta-conglycinin beta(3) was investigated by thermal unfolding experiments using CD spectroscopy. The negative ellipticity of the protein was enhanced with rising solution temperature. The transition temperature of thermal unfolding of the protein (T(m)) was 63.4 degrees C at pH 3.0 (0.15 M KCl). When chitosan was added to the protein solution, the T(m) value was elevated by 7.7 degrees C, whereas the T(m) elevation upon addition of chitosan hexamer (GlcN)(6) was 2.2 degrees C. These carbohydrates appear to interact with the protein stabilizing the protein structure, and the interaction ability could be evaluated from the T(m) elevation. Similar experiments were conducted at various pHs from 2.0 to 3.5, and the T(m) elevation was found to be enhanced in the higher pH region. We conclude that chitosan interacts with beta-conglycinin through electrostatic interactions between the positive charges of the chitosan polysaccharide and the negative charges of the protein surface.

Inhibition of fungal plant pathogens by synergistic action of chito-oligosaccharides and commercially available fungicides

Chitosan is a linear heteropolymer consisting of β 1,4-linked N-acetyl-D-glucosamine (GlcNAc) and D-glucosamine (GlcN). We have compared the antifungal activity of chitosan with DPn (average degree of polymerization) 206 and FA (fraction of acetylation) 0.15 and of enzymatically produced chito-oligosaccharides (CHOS) of different DPn alone and in combination with commercially available synthetic fungicides, against Botrytis cinerea, the causative agent of gray mold in numerous fruit and vegetable crops. CHOS with DPn in the range of 15-40 had the greatest anti-fungal activity. The combination of CHOS and low dosages of synthetic fungicides showed synergistic effects on antifungal activity in both in vitro and in vivo assays. Our study shows that CHOS enhance the activity of commercially available fungicides. Thus, addition of CHOS, available as a nontoxic byproduct of the shellfish industry, may reduce the amounts of fungicides that are needed to control plant diseases.

Ultrasonication and steam-explosion as chitin pretreatments for chitin oligosaccharide production by chitinases of Lecanicillium lecanii

In this study, chitin oligosaccharides have been successfully produced using chitinases from submerged fermentation of Lecanicillium lecanii. The highest Hex, Chit and Prot production was 0.14, 0.26 and 2.05 U/mg of protein, respectively, which were attained varying pH from 5 to 8 after 96 h. Culture conditions conducted at constant pH of 6 resulted in significantly lower enzyme production. The crude enzyme was partially purified by salting out with (NH4)2SO4 followed by size exclusion chromatography to isolate the chitinase mixture for further chitin hydrolysis assays. In this regard, chitin substrates were pretreated with sonication and steam explosion prior to enzymatic reaction. Structural changes were observed with steam explosion with 11.28% reduction of the crystallinity index attained with the lowest chitin/water ratio (0.1g/mL). Pretreated chitins reached the highest production of reducing sugars (0.37 mg/mL) and GlcNAc (0.59 mg/mL) in 23.6% yield.

Biotechnological approaches for field applications of chitooligosaccharides (COS) to induce innate immunity in plants

Plants have evolved mechanisms to recognize a wide range of pathogen-derived molecules and to express induced resistance against pathogen attack. Exploitation of induced resistance, by application of novel bioactive elicitors, is an attractive alternative for crop protection. Chitooligosaccharide (COS) elicitors, released during plant fungal interactions, induce plant defenses upon recognition. Detailed analyses of structure/function relationships of bioactive chitosans as well as recent progress towards understanding the mechanism of COS sensing in plants through the identification and characterization of their cognate receptors have generated fresh impetus for approaches that would induce innate immunity in plants. These progresses combined with the application of chitin/chitosan/COS in disease management are reviewed here. In considering the field application of COS, however, efficient and large-scale production of desired COS is a challenging task. The available methods, including chemical or enzymatic hydrolysis and chemical or biotechnological synthesis to produce COS, are also reviewed.

Substrate recognition and hydrolysis by a family 50 exo-β-agarase, Aga50D, from the marine bacterium Saccharophagus degradans

The bacteria that metabolize agarose use multiple enzymes of complementary specificities to hydrolyze the glycosidic linkages in agarose, a linear polymer comprising the repeating disaccharide subunit of neoagarobiose (3,6-anhydro-l-galactose-α-(1,3)-d-galactose) that are β-(1,4)-linked. Here we present the crystal structure of a glycoside hydrolase family 50 exo-β-agarase, Aga50D, from the marine microbe Saccharophagus degradans. This enzyme catalyzes a critical step in the metabolism of agarose by S. degradans through cleaving agarose oligomers into neoagarobiose products that can be further processed into monomers. The crystal structure of Aga50D to 1.9 Å resolution reveals a (β/α)8-barrel fold that is elaborated with a β-sandwich domain and extensive loops. The structures of catalytically inactivated Aga50D in complex with non-hydrolyzed neoagarotetraose (2.05 Å resolution) and neoagarooctaose (2.30 Å resolution) provide views of Michaelis complexes for a β-agarase. In these structures, the d-galactose residue in the -1 subsite is distorted into a (1)S3 skew boat conformation. The relative positioning of the putative catalytic residues are most consistent with a retaining catalytic mechanism. Additionally, the neoagarooctaose complex showed that this extended substrate made substantial interactions with the β-sandwich domain, which resembles a carbohydrate-binding module, thus creating additional plus (+) subsites and funneling the polymeric substrate through the tunnel-shaped active site. A synthesis of these results in combination with an additional neoagarobiose product complex suggests a potential exo-processive mode of action of Aga50D on the agarose double helix.

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.

Adherence inhibition of enteropathogenic Escherichia coli by chitooligosaccharides with specific degrees of acetylation and polymerization

Some oligosaccharides are known to act as molecular decoys by inhibiting pathogen adherence to epithelial cells. The present study was aimed at analyzing whether chitooligosaccharides (CHOS), that is, oligomers of D-glucosamine and N-acetyl-D-glucosamine, have such antiadherence activity. CHOS of varied degree of polymerization (DP) and fraction of acetylation (F(A)) were produced. Adherence of enteropathogenic Escherichia coli (EPEC) to the surface of a human HEp-2 cell line was determined in the absence or presence of the various CHOS fractions. Adherence was assessed by microscopic counting and image analysis of bacterial clusters and cells. The results showed that all CHOS fractions inhibited adherence of EPEC to HEp-2 cells. Hydrolysates with lower F(A) were more effective at reducing adherence. This effect is greater than that obtained with other oligosaccharides, such as galactooligosaccharides, applied at the same concentrations.

Isolation and characterization of chitosan-producing bacteria from beaches of chennai, India

Chitosan is a deacetylated product of chitin produced by chitin deacetylase, an enzyme that hydrolyses acetamido groups of N-acetylglucosamine in chitin. Chitosan is a natural polymer that has great potential in biotechnology and in the biomedical and pharmaceutical industries. Commercially, it is produced from chitin via a harsh thermochemical process that shares most of the disadvantages of a multistep chemical procedure. It is environmentally unsafe and not easily controlled, leading to a broad and heterogeneous range of products. An alternative or complementary procedure exploiting the enzymatic deacetylation of chitin could potentially be employed, especially when a controlled and well-defined process is required. In this study, 20 strains of bacteria were isolated from soil samples collected from different beaches of Chennai, India. Of these 20 bacterial strains, only 2 strains (S3, S14) are potent degrader of chitin and they are also a good producer of the enzyme chitin deacetylase so as to release chitosan.

Mode of action of a family 75 chitosanase from Streptomyces avermitilis

Chitooligosaccharides (CHOS) are oligomers composed of glucosamine and N-acetylglucosamine with several interesting bioactivities that can be produced from enzymatic cleavage of chitosans. By controlling the degree of acetylation of the substrate chitosan, the enzyme, and the extent of enzyme degradation, CHOS preparations with limited variation in length and sequence can be produced. We here report on the degradation of chitosans with a novel family 75 chitosanase, SaCsn75A from Streptomyces avermitilis . By characterizing the CHOS preparations, we have obtained insight into the mode of action and subsite specificities of the enzyme. The degradation of a fully deacetylated and a 31% acetylated chitosan revealed that the enzyme degrade these substrates according to a nonprocessive, endo mode of action. With the 31% acetylated chitosan as substrate, the kinetics of the degradation showed an initial rapid phase, followed by a second slower phase. In the initial faster phase, an acetylated unit (A) is productively bound in subsite -1, whereas deacetylated units (D) are bound in the -2 subsite and the +1 subsite. In the slower second phase, D-units bind productively in the -1 subsite, probably with both acetylated and deacetylated units in the -2 subsite, but still with an absolute preference for deacetylated units in the +1 subsite. CHOS produced in the initial phase are composed of deacetylated units with an acetylated reducing end. In the slower second phase, higher amounts of low DP fully deacetylated oligomers (dimer and trimer) are produced, while the higher DP oligomers are dominated by compounds with acetylated reducing ends containing increasing amounts of internal acetylated units. The degradation of chitosans with varying degrees of acetylation to maximum extents of degradation showed that increasingly longer oligomers are produced with increasing degree of acetylation, and that the longer oligomers contain sequences of consecutive acetylated units interspaced by single deacetylated units. The catalytic properties of SaCsn75A differ from the properties of a previously characterized family 46 chitosanase from S. coelicolor (ScCsn46A).

Chitosan oligosaccharide as potential therapy of inflammatory bowel disease: therapeutic efficacy and possible mechanisms of action

Inflammatory bowel disease (IBD) results from intestinal epithelial barrier defect and dysregulated mucosal immune response. This study aimed to evaluate the therapeutic potential of chitosan oligosaccharide (COS), a biodegradation product of dietary fiber chitosan, in the treatment of IBD and to elucidate its possible mechanisms of action. Oral administration of COS protected against mortality and intestinal inflammation in a mouse model of acute colitis induced by 5% dextran sulfate sodium (DSS). The most effective dose range of COS was 10-20 mg/kg/day. In addition, nuclear factor kappa B (NF-κB) activation, and levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in colonic tissues were suppressed in mice receiving COS. Similar protective effect of COS against mortality and intestinal inflammation was observed in another mouse model of acute colitis induced by rectal instillation of 4% acetic acid. Importantly, COS administration after colitis induction was effective in ameliorating intestinal inflammation in both acute colitis models induced by 5% DSS and chronic colitis models induced by cycles of 2.5% DSS. In human colonic epithelial cells (T84 cells), COS treatment prevented NF-κB activation, production of TNF-α and IL-6, and loss of epithelial barrier integrity under both lipopolysaccharide (LPS) and TNF-α-stimulated conditions. Furthermore, binding of LPS to T84 cells, and TNF-α and oxidative stress-induced apoptosis of T84 cells were prevented by treatment with COS. These results suggest that COS may be effective in the treatment of IBD through inhibition of NF-κB signaling and apoptosis of intestinal epithelial cells.

Inhibition of angiogenesis by chitooligosaccharides with specific degrees of acetylation and polymerization

Chitooligosaccharides (CHOS) inhibit angiogenesis and may be used in the treatment of cancer tumors. We have studied the effect of the fraction of acetylation (FA) and the degree of polymerization (DP) on CHOS anti-angiogenic activity. We tested enzymatically produced CHOS-mixtures with FA0.15, FA0.3 and FA0.6, and DP≤12 in initial experiments with chorioallantoic membranes. All of the samples reduced the formation of new blood vessels, CHOS with FA0.3 giving the best effect. Single-DP fractions from the FA0.3 sample purified by size-exclusion chromatography (DP3-DP12) were then tested for inhibition of migration of human endothelial cells, which is an important element of the angiogenesis process. All of the fractions inhibited migration, meaning that, within the DP area tested in this study, FA is more important than DP for the effect. Generally, the results reveal that DP3-DP12 CHOS have considerable potential as anti-angiogenic compounds.

Measuring processivity

Natural cellulolytic enzyme systems as well as leading commercial cellulase cocktails are dominated by enzymes that degrade cellulose chains in a processive manner. Despite the abundance of processivity among natural cellulases, the molecular basis as well as the biotechnological implications of this mechanism are only partly understood. One of the major limitations lies in the fact that it is not straightforward to measure and quantify processivity in what essentially are biphasic experimental systems. Here, we describe and discuss both well-established methods and newer methods for measuring cellulase processivity. In addition, we discuss recent insights from studies on chitinases that may help direct further studies on processivity in cellulases.

Human chitotriosidase-catalyzed hydrolysis of chitosan

Chitotriosidase (HCHT) is one of two family 18 chitinases produced by humans, the other being acidic mammalian chitinase (AMCase). The enzyme is thought to be part of the human defense mechanism against fungal parasites, but its precise role and the details of its enzymatic properties have not yet been fully unraveled. We have studied the properties of HCHT by analyzing how the enzyme acts on high-molecular weight chitosans, soluble copolymers of β-1,4-linked N-acetylglucosamine (GlcNAc, A), and glucosamine (GlcN, D). Using methods for in-depth studies of the chitinolytic machinery of bacterial family 18 enzymes, we show that HCHT degrades chitosan primarily via an endoprocessive mechanism, as would be expected on the basis of the structural features of its substrate-binding cleft. The preferences of HCHT subsites for acetylated versus nonacetylated sugars were assessed by sequence analysis of obtained oligomeric products showing a very strong, absolute, and a relative weak preference for an acetylated unit in the -2, -1, and +1 subsites, respectively. The latter information is important for the design of inhibitors that are specific for the human chitinases and also provides insight into what kind of products may be formed in vivo upon administration of chitosan-containing medicines or food products.

Substrate positioning in chitinase A, a processive chito-biohydrolase from Serratia marcescens

The contributions of the -3 subsite and a putative +3 subsite to substrate positioning in ChiA from Serratia marcescens have been investigated by comparing how ChiA and its -3 subsite mutant W167A interact with soluble substrates. The data show that Trp - GlcNAc stacking in the -3 subsite rigidifies the protein backbone supporting the formation of the intermolecular interaction network that is necessary for the recognition and positioning of the N-acetyl groups before the -1 subsite. The +3 subsite exhibits considerable substrate affinity that may promote endo-activity in ChiA and/or assist in expelling dimeric products from the +1 and +2 subsites during processive hydrolysis.

Analysis of noncovalent chitinase-chito-oligosaccharide complexes by infrared-matrix assisted laser desorption ionization and nanoelectrospray ionization mass spectrometry

Transferring noncovalently bound complexes from the condensed phase into the gas phase represents a challenging task due to weak intermolecular bonds that have to be maintained during the phase transition. Currently, electrospray ionization (ESI) is the standard mass spectrometric (MS) technique to analyze noncovalent complexes. Although infrared matrix-assisted laser desorption ionization (IR-MALDI)-MS also provides particular soft desorption/ionization conditions, this method has so far hardly been applied for the analysis of noncovalent complexes. In this study, we employed IR-MALDI orthogonal time-of-flight (o-TOF)-MS in combination with the liquid matrix glycerol to characterize the specific complex formation of chito-oligosaccharide (CHOS) ligands with two variants of Chitinase A (ChiA) from Serratia marcescens, the inactive E315Q mutant and the active W167A mutant, respectively. The IR-MALDI-o-TOF-MS results were compared to those obtained using nano-ESI-quadrupole (q)-TOF-MS and ultraviolet (UV)-MALDI-o-TOF-MS. Using IR-MALDI-o-TOF-MS, specific noncovalent complexes between ChiA and CHOS were detected with distributions between enzymes with bound oligosaccharides vs free enzymes that were essentially identical to those obtained by nano-ESI-q-TOF-MS. Chitinase-CHOS complexes were not detected when UV-MALDI was employed for desorption/ionization. The results show that IR-MALDI-MS can be a valuable tool for fast and simple screening of noncovalent enzyme-ligand interactions.

Crystal structure and mode of action of a class V chitinase from Nicotiana tabacum

A class V chitinase from Nicotiana tabacum (NtChiV) with amino acid sequence similar to that of Serratia marcescens chitinase B (SmChiB) was expressed in E. coli and purified to homogeneity. When N-acetylglucosamine oligosaccharides [(NAG)(n)] were hydrolyzed by the purified NtChiV, the second glycosidic linkage from the non-reducing end was predominantly hydrolyzed in a manner similar to that of SmChiB. NtChiV was shown to hydrolyze partially N-acetylated chitosan non-processively, whereas SmChiB hydrolyzes the same substrate processively. The crystal structure of NtChiV was determined by the single-wavelength anomalous dispersion method at 1.2 Å resolution. The protein adopts a classical (β/α)₈-barrel fold (residues 1-233 and 303-348) with an insertion of a small (α + β) domain (residues 234-302). This is the first crystal structure of a plant class V chitinase. The crystal structure of the inactive mutant NtChiV E115Q complexed with (NAG)₄ was also solved and exhibited a linear conformation of the bound oligosaccharide occupying -2, +1, +2, and +3 subsites. The complex structure corresponds to an initial state of (NAG)₄ binding, which is proposed to be converted into a bent conformation through sliding of the +1, +2, and +3 sugar units to -1, +1, and +2 subsites. Although NtChiV is similar to SmChiB, the chitin-binding domain is present in the C-terminus of the latter, but not in the former. Aromatic amino acid residues found in the substrate binding cleft of SmChiB, including Trp97, are substituted with aliphatic residues in NtChiV. These structural differences appear to be responsible for NtChiV being a non-processive enzyme.

Degradation of chitosans with a family 46 chitosanase from Streptomyces coelicolor A3(2)

We have studied the degradation of well-characterized soluble heteropolymeric chitosans by a novel family 46 chitosanase, ScCsn46A from Streptomyces coelicolor A3(2), to obtain insight into the enzyme's mode of action and to determine its potential for production of different chitooligosaccharides. The degradation of both a fully deacetylated chitosan and a 32% acetylated chitosan showed a continuum of oligomeric products and a rapid disappearance of the polymeric fraction, which is diagnostic for a nonprocessive endomode of action. The kinetics of the degradation of the 32% acetylated chitosan demonstrated an initial rapid phase and a slower second phase, in addition to a third and even slower kinetic phase. The first phase reflects the cleavage of the glycosidic linkage between two deacetylated units (D-D), the primary products being fully deacetylated dimers, trimers, and tetramers, as well as longer oligomers with increasing degrees of acetylation. In the subsequent slower kinetic phases, oligomers with a higher degree of acetylated units (A) appear, including oligomers with A's at the reducing or nonreducing end, which indicate that there are no absolute preferences for D in subsites -1 and +1. After maximum degradation of the chitosan, the dimers DA and DD were the dominant products. The degradation of chitosans with varying degrees of acetylation to a maximum degree of scission showed that ScCsn46A could degrade all chitosan substrates extensively, although to decreasing degrees of scission with increasing F(A). The potential use of ScCsn46A to prepare fully deacetylated oligomers and more highly acetylated oligomers from chitosan substrates with varying degrees of acetylation is discussed.

Application of spectroscopic methods for structural analysis of chitin and chitosan

Chitin, the second most important natural polymer in the world, and its N-deacetylated derivative chitosan, have been identified as versatile biopolymers for a broad range of applications in medicine, agriculture and the food industry. Two of the main reasons for this are firstly the unique chemical, physicochemical and biological properties of chitin and chitosan, and secondly the unlimited supply of raw materials for their production. These polymers exhibit widely differing physicochemical properties depending on the chitin source and the conditions of chitosan production. The presence of reactive functional groups as well as the polysaccharide nature of these biopolymers enables them to undergo diverse chemical modifications. A complete chemical and physicochemical characterization of chitin, chitosan and their derivatives is not possible without using spectroscopic techniques. This review focuses on the application of spectroscopic methods for the structural analysis of these compounds.

Production of chitooligosaccharides and their potential applications in medicine

Chitooligosaccharides (CHOS) are homo- or heterooligomers of N-acetylglucosamine and D-glucosamine. CHOS can be produced using chitin or chitosan as a starting material, using enzymatic conversions, chemical methods or combinations thereof. Production of well-defined CHOS-mixtures, or even pure CHOS, is of great interest since these oligosaccharides are thought to have several interesting bioactivities. Understanding the mechanisms underlying these bioactivities is of major importance. However, so far in-depth knowledge on the mode-of-action of CHOS is scarce, one major reason being that most published studies are done with badly characterized heterogeneous mixtures of CHOS. Production of CHOS that are well-defined in terms of length, degree of N-acetylation, and sequence is not straightforward. Here we provide an overview of techniques that may be used to produce and characterize reasonably well-defined CHOS fractions. We also present possible medical applications of CHOS, including tumor growth inhibition and inhibition of T(H)2-induced inflammation in asthma, as well as use as a bone-strengthener in osteoporosis, a vector for gene delivery, an antibacterial agent, an antifungal agent, an anti-malaria agent, or a hemostatic agent in wound-dressings. By using well-defined CHOS-mixtures it will become possible to obtain a better understanding of the mechanisms underlying these bioactivities.

N-Acetyl-D-glucosamine oligosaccharides induce mucin secretion from colonic tissue and induce differentiation of human keratinocytes

Chitin oligosaccharides (DP2, DP3, DP4, DP5 and DP7) were investigated for their effects on epithelial cells and tissue (skin keratinocytes in-vitro and ex-vivo, and gastrointestinal epithelial membranes ex-vivo). Oligomers DP2, DP3 and DP5 at 10 μg mL−1 significantly stimulated the mitochondrial activity of cultured keratinocytes in-vitro (primary cells and HaCaT cell line), with highest activity observed for the pentamer (150% of untreated control). The effects were dose dependent. This higher energy status of primary cells was triggered into a higher differentiation status, as determined by the early and late differentiation markers keratins K1/K10 and involucrin, respectively. In contrast, increased mitogenic cell proliferation was not induced by the oligosaccharides. Toxic effects on keratinocytes were absent. Additionally for the first time a mucin-stimulating effect of chitin oligosaccharides DP3 and DP5 was observed in an ex-vivo model based on intestinal epithelial mucosa tissue. Mucin secretion was time dependent, leading to the secretion of polymers comparable to those normally secreted under physiological conditions. Mucin induction was observed from colonic tissue isolated from humans and pigs. Also, porcine stomach mucosa was stimulated by DP5, while ileum tissue reacted to only a minor extent. Potential developments towards products with wound-healing capacity and activity against chronic bowel disease are discussed.

Degradation of chitosans with chitinase G from Streptomyces coelicolor A3(2): production of chito-oligosaccharides and insight into subsite specificities

We have studied the degradation of soluble heteropolymeric chitosans with a bacterial family 19 chitinase, ChiG from Streptomyces coelicolor A3(2), to obtain insight into the mode of action of ChiG, to determine subsite preferences for acetylated and deacetylated sugar units, and to evaluate the potential of ChiG for production of chito-oligosaccharides. Degradation of chitosans with varying degrees of acetylation was followed using NMR for the identity (acetylated/deacetylated) of new reducing and nonreducing ends as well as their nearest neighbors and using gel filtration to analyze the size distribution of the oligomeric products. Degradation of a 64% acetylated chitosan yielded a continuum of oligomers, showing that ChiG operates according to a nonprocessive, endo mode of action. The kinetics of the degradation showed an initial rapid phase dominated by cleavage of three consecutive acetylated units (A; occupying subsites -2, -1, and +1), and a slower kinetic phase reflecting the cleavage of the glycosidic linkage between a deacetylated unit (D, occupying subsite -1) and an A (occupying subsite +1). Characterization of isolated oligomer fractions obtained at the end of the initial rapid phase and at the end of the slower kinetic phase confirmed the preference for A binding in subsites -2, -1, and +1 and showed that oligomers with a deacetylated reducing end appeared only during the second kinetic phase. After maximum conversion of the chitosan, the dimers AD/AA and the trimer AAD were the dominating products. Degradation of chitosans with varying degrees of acetylation to maximum degree of scission produced a wide variety of oligomer mixtures, differing in chain length and composition of acetylated/deacetylated units. These results provide insight into the properties of bacterial family 19 chitinases and show how these enzymes may be used to convert chitosans to several types of chito-oligosaccharide mixtures.