Hydrolysis of chitin and chitosans by the human chitinolytic enzymes: chitotriosidase, acidic mammalian chitinase, and lysozyme

Human chitinolytic enzymes trigger growing interest, not only because a wide range of diseases and allergic responses are linked to chitinous components of pathogens, including their interplay with human enzymes, but also due to the increasing use of chitosans in biomedical applications. Here, we present a detailed side-by-side analysis of the only two human chitinases, chitotriosidase and acidic mammalian chitinase, as well as human lysozyme. By analyzing the cleavage of well-characterized chitosan polymers and defined chitin and chitosan oligomers, we report mild processivity and a quantitative subsite preference typical for GH18 chitinases for chitotriosidase and acidic mammalian chitinase. In contrast, lysozyme is negligibly processive and preferentially binds acetylated units at subsites -2, -1, and +1, thus exhibiting an even higher overall preference for acetylated units. A common feature of all three enzymes is their endo-chitinase behavior. For efficient hydrolysis, chitotriosidase or lysozyme require substrates of ≥4 or ≥5 units, respectively, and we identified defined chitosan oligomers which can competitively inhibit chitotriosidase. Knowledge about the enzymes' actions provides insight into the metabolic fate of chitin and chitosans in the human body, which is crucial to develop and approve chitosan applications, and to elucidate molecular mechanisms in chitin-associated diseases.

Fabrication of Chitosan/PEGDA Bionanocomposites for Enhanced Drug Encapsulation and Release Efficiency

Drug delivery systems (DDS) have evolved in the last decades with the development of hydrogels and particles. However, challenges such as high systemic uptake, side effects, low bioavailability, and encapsulation efficiency continue to be significant hurdles faced by such DDSs. Particles and hydrogels can be specifically designed for targeted DDSs to mitigate some of these problems. This study developed chitosan (Cs) particles (Ps) and composite films using poly(ethylene glycol) diacrylate (PEGDA) as a copolymer to encapsulate gentamicin (GtS) for drug delivery. We demonstrated that lysozyme degrades the chitosan β-1,4 glycosidic bonds to release GtS. PEGDA increased drug encapsulation efficiency by shielding the repelling forces of like charges between Cs and GtS. The data show that PEGDA does not hinder enzymatic degradation while increasing drug encapsulation efficiency and producing more homogeneous particles. Additionally, we utilized Michael's reaction to cross-link Cs, CsPs, and PEGDA to produce a film designed for drug delivery. The film is an anchor for CsPs to prevent premature drug release. The cross-linking of Cs and PEGDA does not affect lysozyme activity, and CsPs could successfully release GtS without affecting GtS activity.

Chitosan-based coatings with tunable transparency and superhydrophobicity: A solvent-free and fluorine-free approach by stearoyl derivatization

One of the current greatest challenges in materials science and technology is the development of safe- and sustainable-by-design coatings with enhanced functionalities, e.g. to substitute fluorinated substances raising concerns for their potential hazard on human health. Bio-based polymeric coatings represent a promising route with a high potential. In this study, we propose an innovative sustainable method for fabricating coatings based on chitosan with modified functionality, with a fine-tuning of coating properties, namely transparency and superhydrophobicity. The process consists in two main steps: i) fluorine-free modification of chitosan functional groups with stearoyl chloride and freeze-drying to obtain a superhydrophobic powder, ii) coating deposition using a novel solvent-free approach through a thermal treatment. The modified chitosan is characterized to assess its chemico-physical properties and confirm the functionality modification with fatty acid tails. The deposition method enables tuning the coating properties of transparency and superhydrophobicity, maintaining good durability.

Biotechnologically produced chitosans with nonrandom acetylation patterns differ from conventional chitosans in properties and activities

Chitosans are versatile biopolymers with multiple biological activities and potential applications. They are linear copolymers of glucosamine and N-acetylglucosamine defined by their degree of polymerisation (DP), fraction of acetylation (F_A), and pattern of acetylation (PA). Technical chitosans produced chemically from chitin possess defined DP and F_A but random PA, while enzymatically produced natural chitosans probably have non-random PA. This natural process has not been replicated using biotechnology because chitin de-N-acetylases do not efficiently deacetylate crystalline chitin. Here, we show that such enzymes can partially N-acetylate fully deacetylated chitosan in the presence of excess acetate, yielding chitosans with F_A up to 0.7 and an enzyme-dependent non-random PA. The biotech chitosans differ from technical chitosans both in terms of physicochemical and nanoscale solution properties and biological activities. As with synthetic block co-polymers, controlling the distribution of building blocks within the biopolymer chain will open a new dimension of chitosan research and exploitation.

Optimizing Chitin Depolymerization by Lysozyme to Long-Chain Oligosaccharides

Chitin oligosaccharides (COs) hold high promise as organic fertilizers in the ongoing agro-ecological transition. Short- and long-chain COs can contribute to the establishment of symbiotic associations between plants and microorganisms, facilitating the uptake of soil nutrients by host plants. Long-chain COs trigger plant innate immunity. A fine investigation of these different signaling pathways requires improving the access to high-purity COs. Here, we used the response surface methodology to optimize the production of COs by enzymatic hydrolysis of water-soluble chitin (WSC) with hen egg-white lysozyme. The influence of WSC concentration, its acetylation degree, and the reaction time course were modelled using a Box–Behnken design. Under optimized conditions, water-soluble COs up to the nonasaccharide were formed in 51% yield and purified to homogeneity. This straightforward approach opens new avenues to determine the complex roles of COs in plants.

Lysozyme-Responsive Spray-Dried Chitosan Particles for Early Detection of Wound Infection

Infections are a severe health issue, and the need for an early point-of-care diagnostic approach for wound infections is continuously growing. Lysozyme has shown a great potential as a biomarker for rapid detection of wound infection. In this study, spray-drying of labeled and derivatized chitosans was investigated for the production of small particles responsive to lysozyme. Therefore, various chitosans, differing in their origin (snow crab, Chionoecetes sp., with medium and low molecular weight or shrimp) were N-acetylated, labeled with reactive black 5, and tested for solubility and spray-drying suitability. Reactive black-5-stained N-acetylated chitosan (low molecular weight, origin crab) was successfully spray-dried, and the obtained particles were characterized regarding size, ζ potential, and morphology. The particles showed an average hydrodynamic radius of 612.5 ± 132.8 nm. ζ potential was measured in the context of a later application as an infection detection system for wound infections in artificial wound fluid (-6.14 ± 0.16 mV) and infected wound fluid (-7.93 ± 1.35 mV). Furthermore, the aggregation behavior and surface structure were analyzed by using scanning electron microscopy and confocal laser scanning microscopy revealing spherical-shaped particles with explicit surface topologies. Spray-dried N-acetylated chitosan particles showed a 5-fold increase in lysozyme-responsive release of dyed chitosan fragments due to the enhanced surface area to volume ratio when compared to non-spray-dried N-acetylated chitosan flakes. On the basis of these results, the study showed the improved properties of N-acetylated spray-dried chitosan particles for future applications for early and rapid infection detection.

Fabrication of biodegradable nano test tubes by template synthesis

Aims: Recent publications have suggested that cylindrically shaped drug-delivery carriers have an advantage over carriers based on spherical particles in both blood circulation and cell internalization rates. For this reason, this article introduces a method to fabricate hollow, uniform, biodegradable chitosan nano test tubes for applications in drug delivery. Methods: A nanoporous alumina template membrane was used to fabricate hollow chitosan nano test tubes. The chitosan nano test tubes were crosslinked with a disulfide cleavable crosslinker before being removed from the alumina template membrane. We explored two mechanisms for degrading the chitosan nano test tubes – enzymatic degradation by lysozyme and cleavage of the disulfide bond in the crosslinking agent. Results: The template synthesis method resulted in the fabrication of uniform hollow chitosan nano test tubes whose dimensions were easily manipulated based on the dimensions of the pores in the alumina template membrane. The tubes were degraded upon exposure to either lysozyme or sulfhydryl-containing reducing reagents. Conclusion: These tubes have potential for drug-delivery applications. The fact that these tubes degrade upon exposure to a sulfhydryl-containing reducing agent allows for a mechanism for intercellular drug delivery as the tubes should degrade in the presence of intercellular glutathione.

Development and application of a model for chitosan hydrolysis by a family 18 chitinase

Hydrolysis of partially deacetylated chitosans by ChitinaseB (ChiBeta) from Serratia marcescens results in mixtures of oligosaccharides typically between 2 and 20 sugar residues. The amounts of different oligomer fractions depend on the degree of acetylation of the starting chitosans. We have used experimentally determined distributions of hydrolysis products to develop a model for chitosan hydrolysis by ChiB. Important elements of the model include interaction parameters for acetylated/deacetylated units in each of the six subsites in the active cleft and degree of processivity (multiple attack). The hydrolysis reaction is described as a chemical reaction with an activation barrier that depends on the substrate sequence presented to the enzyme subsites. Using a Monte Carlo approach, the interaction parameters were refined by minimizing the difference between observed and predicted amounts of hydrolysis products obtained upon degradation of chitosan with a degree of acetylation of 65%. The final model can accurately predict complex patterns of oligosaccharides produced in the hydrolysis of chitosans with various degrees of acetylation, as well as patterns observed during reactions with chito-oligosaccharides. The behavior of a ChiB mutant with a mutation in subsite +2 (Gly188Asp), which reduces the affinity for an acetylated sugar, could be predicted correctly by introducing one single change in the model parameters (the interaction energy for an acetylated unit in the +2 subsite). The proposed model may be used to explore degradation products for different enzyme-substrates combinations and to optimize conditions for preparation of specific oligosaccharides. In addition, the model provides insight into subsite interaction parameters and the degree of processivity, which complements previous experimental studies on the mode of action of ChiB.

The recombinant Azotobacter vinelandii mannuronan C-5-epimerase AlgE4 epimerizes alginate by a nonrandom attack mechanism

The Ca2+-dependent mannuronan C-5-epimerase AlgE4 is a representative of a family of Azotobacter vinelandii enzymes catalyzing the polymer level epimerization of beta-D-mannuronic acid (M) to alpha-L-guluronic acid (G) in the commercially important polysaccharide alginate. The reaction product of recombinantly produced AlgE4 is predominantly characterized by an alternating sequence distribution of the M and G residues (MG blocks). AlgE4 was purified after intracellular overexpression in Escherichia coli, and the activity was shown to be optimal at pH values between 6.5 and 7.0, in the presence of 1-3 mM Ca2+, and at temperatures near 37 degrees C. Sr2+ was found to substitute reasonably well for Ca2+ in activation, whereas Zn2+ strongly inhibited the activity. During epimerization of alginate, the fraction of GMG blocks increased linearly as a function of the total fraction of G residues and comparably much faster than that of MMG blocks. These experimental data could not be accounted for by a random attack mechanism, suggesting that the enzyme either slides along the alginate chain during catalysis or recognizes a pre-existing G residue as a preferred substrate in its consecutive attacks.

In vitro degradation rates of partially N-acetylated chitosans in human serum

The initial degradation rates (r) in human serum of three chitosans with FA = 0.42, 0.51, and 0.60 were determined by measuring the decrease in viscosity as a function of time. A strong increase in r with increasing FA of the chitosans was observed, with r increasing proportionally to FA4.5. With increasing concentrations of lysozyme added to the reaction mixtures of chitosan and serum, the relative increase in degradation rate of chitosans with increasing FA was almost the same as that without lysozyme added. Addition of the chitinase inhibitor allosamidin (50 microM) did not inhibit the degradation rate of chitosan (FA = 0.60) by human serum. The results suggest that chitosans are actually mainly depolymerized by lysozyme in human serum, and not by other enzymes or other depolymerization mechanisms.

Determination of enzymatic hydrolysis specificity of partially N-acetylated chitosans

A new method for determining the specificity of hydrolysis of the linear binary heteropolysaccharide chitosan composed of (1-->4)-linked 2-acetamido-2-deoxy-beta-D-glucopyranose (GlcNAc; A-unit) and 2-amino-2-deoxy-beta-D-glucopyranose (GlcN; D-unit) residues is described. The method is based on the assignments of the 13C chemical shifts of the identity (A- or D-units) of the new reducing and non-reducing ends and the variation in their nearest neighbours, using low molecular weight chitosans with known random distribution of A- and D-units as substrate. A highly N-acetylated chitosan with fraction of acetylated units (FA) of 0.68 and a number-average degree of polymerization (DPn) of 30 was hydrolysed with hen egg-white lysozyme, showing that both the new reducing and non-reducing ends consisted exclusively of A-units, indicating a high specificity for A-units in subsites DL and EL on lysozyme. Our data suggests that the preceding unit of the reducing A-units, is invariable, and based on earlier studies, most probably an A-unit, while the unit following the non-reducing A-units can be either an A- or a D-unit. A more detailed study of the specificity of lysozyme at subsite DL was performed by hydrolyzing a more deacetylated chitosan (FA = 0.35 and DPn of 20) to a DPn of 9, showing that even for this chitosan more than 90% of the new reducing ends were acetylated units. Thus, lysozyme depolymerizes partially N-acetylated chitosans by preferentially hydrolyzing sequences of acetylated units bound to site CL, DL and EL of the active cleft, while there is no specificity between acetylated and deacetylated units to site FL. In addition, a moderately N-acetylated chitosan with fraction of acetylated units (FA) of 0.35 and a DPn of 20 was hydrolysed with Bacillus sp. No. 7-M chitosanase, showing that both the new reducing and non-reducing ends consisted exclusively of D-units. Our data suggests that the nearest neigbour to the D-unit at the reducing end is invariable, and based on earlier studies, most probably a D-unit, while the unit following the non-reducing D-units can be either an A- or a D-unit. We conclude that the Bacillus chitosanase hydrolyzes partially N-acetylated chitosan by preferentially attacking sequences of three consecutive deacetylated units, hypothetical subsites CC, DC and EC, where the cleavage occur between sugar units bound to subsites DC and EC. A hypothetical subsite FC on the chitosanase show no specificity with respect to A- and D-units. The new NMR method described herein offers a time and labour-saving alternative to the procedure of extensive hydrolysis of the binary heteropolysaccharide chitosan and subsequent isolation and characterization of the oligosaccharides.