The roles of the C-terminal domain and type III domains of chitinase A1 from Bacillus circulans WL-12 in chitin degradation

Role of fibronectin type III domain in enhancing the substrate accessibility of modular GH9 endocellulase by reducing non-specific binding to lignin

Utilizing lignocellulosic biomass effectively can lessen reliance on fossil fuels and facilitate the production of second-generation biorefinery feedstocks. The nonspecific binding of lignin to cellulases is one of the main factors affecting their enzymatic performance and hampering their efficiency in degrading lignocellulose. Processive endocellulase from Acidothermus cellulolyticus 11B has a modular structure consisting of several carbohydrate-binding modules, a glycoside hydrolase family 9 catalytic domain, and a fibronectin type III (FN3) domain. This study investigated the role of the FN3 in the degradation of lignocellulose by constructing multiple mutants. The results showed that the FN3 could improve the thermal stability of the enzyme and resist the nonspecific binding of lignin to cellulase. This characteristic can significantly increase the lignocellulose's enzymatic efficiency and offer a novel approach to the artificial design of multi-modular cellulases.

Enhanced degradation of insoluble chitin: Engineering high-efficiency chitinase fusion enzymes for sustainable applications

N-acetyl-D-glucosamine and its dimer are degradation products of chitin waste with great potential in therapeutic and agricultural applications. However, the hydrolysis of insoluble chitin by chitinases remains a major bottleneck. This study investigated the biochemical properties and catalytic mechanisms of PoChi chitinase obtained from Penicillium oxalicum with a focus on enhancing its efficiency during the degradation of insoluble chitin. Recombinant plasmids were engineered to incorporate chitin-binding (ChBD) and/or fibronectin III (FnIII) domains. Notably, PoChi-FnIII-ChBD exhibited the highest substrate affinity (Km = 2.7 mg/mL) and a specific activity of 15.4 U/mg, which surpasses those of previously reported chitinases. These findings highlight the potential of engineered chitinases in advancing industrial biotechnology applications and offer a promising approach to more sustainable chitin waste management.

Functional role of carbohydrate-binding modules in multi-modular chitinase OfChtII

The primary distinction between insect and bacterial chitin degradation systems lies in the presence of a multi-modular endo-acting chitinase ChtII, in contrast to a processive exo-acting chitinase. Although the essential role of ChtII during insect development and its synergistic action with processive chitinase during chitin degradation has been established, the mechanistic understanding of how it deconstructs chitin remains largely elusive. Here OfChtII from the insect Ostrinia furnacalis was investigated employing comprehensive approaches encompassing biochemical and microscopic analyses. The results demonstrated that OfChtII truncations with more carbohydrate-binding modules (CBMs) exhibited enhanced hydrolysis activity, effectively yielding a greater proportion of fibrillary fractions from the compacted chitin substrate. At the single-molecule level, the CBMs in these OfChtII truncations have been shown to primarily facilitate chitin substrate association rather than dissociation. Furthermore, a greater number of CBMs was demonstrated to be essential for the enzyme to effectively bind to chitin substrates with high crystallinity. Through real-time imaging by high-speed atomic force microscopy, the OfChtII-B4C1 truncation with three CBMs was observed to shear chitin fibers, thereby generating fibrillary fragments and deconstructing the compacted chitin structure. This work pioneers in revealing the nanoscale mechanism of endo-acting multi-modular chitinase involved in chitin degradation, which provides an important reference for the rational design of chitinases or other glycoside hydrolases.

The chitin-binding domain of Bacillus thuringiensis ChiA74 inhibits gram-negative bacterial and fungal pathogens of humans and plants

The chitinase ChiA74 is synthesized by Bacillus thuringiensis and possesses a modular organization composed of four domains. In the C-terminal of the enzyme is located the chitin-binding domain (CBD), which has not been isolated as a single unit or characterized. Here, we aimed to isolate the ChiA74's CBD as a single unit, determine the binding properties, and evaluate its antimicrobial and hemolytic activities. We cloned the ChiA74's CBD and expressed it in Escherichia coli BL21. The single domain was purified, analyzed by SDS-PAGE, and characterized. The recombinant CBD (rCBD) showed a molecular mass of ∼14 kDa and binds strongly to α-chitin, with Kd and Bmax of ∼4.7 ± 0.9 μM and 1.5 ± 0.1 μmoles/g chitin, respectively. Besides, the binding potential (Bmax/Kd) was stronger for α-chitin (∼0.31) than microcrystalline cellulose (∼0.19). It was also shown that the purified rCBD inhibited the growth of the clinically relevant Gram-negative bacteria (GNB) Vibrio cholerae, and V. parahemolyticus CVP2 with minimum inhibitory concentrations (MICs) of 121 ± 9.9 and 138 ± 3.2 μg/mL, respectively, and of one of the most common GNB plant pathogens, Pseudomonas syringae with a MIC of 230 ± 13.8 μg/mL. In addition, the rCBD possessed antifungal activity inhibiting the conidia germination of Fusarium oxysporum (MIC = 192 ± 37.5 μg/mL) and lacked hemolytic and agglutination activities against human erythrocytes. The significance of this work lies in the fact that data provided here show for the first time that ChiA74's CBD from B. thuringiensis has antimicrobial activity, suggesting its potential use against significant pathogenic microorganisms. Future works will be focused on testing the inhibitory effect against other pathogenic microorganisms and elucidating the mechanism of action.

Genomic analysis and chitinase characterization of Vibrio harveyi WXL538: insight into its adaptation to the marine environment

Chitin, the most abundant bio-polymer in seawater, may be utilized by various microorganisms as a carbon source. Vibrios have been regarded as one of the main groups of chitin consumers in the marine carbon cycle and chitinase producers. The organisms are widely distributed in the aquatic environment. However, the co-working mechanism between their chitinases, and whether the chitinase's diversity contributes to their adaption to the environment, needs to be further elucidated. Here, we obtained a chitinolytic strain, Vibrio harveyi WXL538 with eight putative chitinase-coding genes. Five of the genes, i.e., Chi4733, Chi540, Chi4668, Chi5174, and Chi4963, were overexpressed and validated, in which Chi4668, Chi4733 and Chi540 were purified and characterized. The result of Chi4668 was described in our previous study. Endo-chitinase Chi4733 degraded colloidal chitin to produce (GlcNAc)2 and minor (GlcNAc)3. The enzymatic activity of Chi4733 was 175.5 U mg-1 and Kcat/Km was 54.9 s-1 M-1. Chi4733 had its maximum activity at 50°C and pH 4-6, activated by Sr2+, Co2+, Ca2+, and Mg2+ and inhibited by Al3+, Zn2+, Cu2+, Ni2+, and SDS. Exo-chitinase Chi540 degraded colloidal chitin to (GlcNAc)2. The enzymatic activity of Chi540 was 134.5 U mg-1 and Kcat/Km was 54.9 s-1 M-1. Chi540 had its maximum activity at 60°C and pH 6-8, was activated by Sr2+, Ca2+, and Mg2+ but inhibited by K+, Ba2+, Zn2+, Cu2+, Ni2+, SDS and urea. Whole genome analysis of V. harveyi WXL538 and characterization of its chitinase can provide a better understanding of its adaptability to the changing marine environment.

Interactions of azole-based inhibitors with human heme oxygenase

Human heme oxygenase-1 (hHO-1) plays a crucial role in human physiology because of its ability to metabolize free heme. The heme degradation products, biliverdin and bilirubin, were shown to have protective antioxidant properties in cells. In the context of cancer, hHO-1 function grants cancer cells defense from standard chemotherapy treatments, leading to the development of azole-based inhibitors that target hHO-1 for potential anticancer therapy. This work reports experimental and theoretical characterization of interactions between three azole-based inhibitors and the active site of hHO-1. It was found that all three compounds have Kd values within the μM order. The electronic absorption and resonance Raman (rR) spectra indicated that they bind to the ferric heme and coordinate through a nitrogen atom. rR measurements revealed varying effects of inhibitors on the geometry of heme vinyl groups in the ferric form of hHO-1. Changes in peripheral group orientation are known to affect heme redox potential, and consequently can reflect the inhibitory properties of studied azoles. The subsequent docking studies showed that inhibitors with lower Kd values are located close to two vinyl groups, while the compound with higher Kd is situated near only one, consistent with the rR studies. Finally, the rR studies of the CO adducts showed that the inhibitors bind to the heme in a reversible manner. Altogether, the combination of ligand binding studies, UV-Vis and rR spectroscopies, as well as computational approach revealed an importance of the steric hindrance imposed by the inhibitor's side chain.

The stress effect of atrazine on the inducible defense traits of Daphnia pulex in response to fish predation risk: Evidences from morphology, life history traits, and expression of the defense-related genes

Herbicide pollution is persistent, which not only has a negative impact on individual organisms, but also may endanger the interspecific relationship between predators and prey. Cladocerans, i.e. zooplankton that plays an important role in the energy flow and material circulation in freshwater ecosystem, usually develop induced defense in response to predation risk. We used atrazine, one of the most used herbicides in the world, and Daphnia pulex, a representative cladocerans, to test the possible interference effect of herbicides on the induced defensive traits of cladocerans in response to predator fish (Rhodeus ocellatus) kairomone, including morphological defense, life history strategies, and the expression of defense-related genes. Atrazine reduced the body size, spine size, growth rate, total offspring, and the relative reproductive output of D. pulex, which further affected the response strength of the morphological and life history defenses, i.e., atrazine significantly reduced the spine size, relative spine size, and fecundity of D. pulex in response to R. ocellatus kairomone. Exposure to atrazine affected the expression of defense-related genes, and we speculated that atrazine affected the signaling process in the induced anti-predation defense of cladocerans. Specially, fish kairomone attenuated the negative effects of high concentrations of atrazine on the life history traits of D. pulex. Our results will help to accurately assess the potential risk of artificial compounds in freshwater ecosystems from the perspective of interspecific relationships, and help to understand the impact of environmental changes on the inducible anti-predator defense of prey in aquatic ecosystems.

Identification and Characterization of Three Chitinases with Potential in Direct Conversion of Crystalline Chitin into N,N′-diacetylchitobiose

Chitooligosaccharides (COSs) have been widely used in agriculture, medicine, cosmetics, and foods, which are commonly prepared from chitin with chitinases. So far, while most COSs are prepared from colloidal chitin, chitinases used in preparing COSs directly from natural crystalline chitin are less reported. Here, we characterize three chitinases, which were identified from the marine bacterium Pseudoalteromonas flavipulchra DSM 14401^T, with an ability to degrade crystalline chitin into (GlcNAc)₂ (N,N’-diacetylchitobiose). Strain DSM 14401 can degrade the crystalline α-chitin in the medium to provide nutrients for growth. Genome and secretome analyses indicate that this strain secretes six chitinolytic enzymes, among which chitinases Chia4287, Chib0431, and Chib0434 have higher abundance than the others, suggesting their importance in crystalline α-chitin degradation. These three chitinases were heterologously expressed, purified, and characterized. They are all active on crystalline α-chitin, with temperature optima of 45–50 °C and pH optima of 7.0–7.5. They are all stable at 40 °C and in the pH range of 5.0–11.0. Moreover, they all have excellent salt tolerance, retaining more than 92% activity after incubation in 5 M NaCl for 10 h at 4 °C. When acting on crystalline α-chitin, the main products of the three chitinases are all (GlcNAc)₂, which suggests that chitinases Chia4287, Chib0431, and Chib0434 likely have potential in direct conversion of crystalline chitin into (GlcNAc)₂.

Response of Coastal Shewanella and Duganella Bacteria to Planktonic and Terrestrial Food Substrates

Global warming scenarios indicate that in subarctic regions, the precipitation will increase in the future. Coastal bacteria will thus receive increasing organic carbon sources from land runoff. How such changes will affect the function and taxonomic composition of coastal bacteria is poorly known. We performed a 10-day experiment with two isolated bacteria: Shewanella baltica from a seaside location and Duganella sp. from a river mouth, and provided them with a plankton and a river extract as food substrate. The bacterial growth and carbon consumption were monitored over the experimental period. Shewanella and Duganella consumed 40% and 30% of the plankton extract, respectively, while the consumption of the river extract was low for both bacteria, ∼1%. Shewanella showed the highest bacterial growth efficiency (BGE) (12%) when grown on plankton extract, while when grown on river extract, the BGE was only 1%. Duganella showed low BGE when grown on plankton extract (< 1%) and slightly higher BGE when grown on river extract (2%). The cell growth yield of Duganella was higher than that of Shewanella when grown on river extract. These results indicate that Duganella is more adapted to terrestrial organic substrates with low nutritional availability, while Shewanella is adapted to eutrophied conditions. The different growth performance of the bacteria could be traced to genomic variations. A closely related genome of Shewanella was shown to harbor genes for the sequestration of autochthonously produced carbon substrates, while Duganella contained genes for the degradation of relatively refractive terrestrial organic matter. The results may reflect the influence of environmental drivers on bacterial community composition in natural aquatic environments. Elevated inflows of terrestrial organic matter to coastal areas in subarctic regions would lead to increased occurrence of bacteria adapted to the degradation of complex terrestrial compounds with a low bioavailability.

Structure-function characterization of the mono- and diheme forms of MhuD, a noncanonical heme oxygenase from Mycobacterium tuberculosis

MhuD is a noncanonical heme oxygenase (HO) from Mycobacterium tuberculosis (Mtb) that catalyzes unique heme degradation chemistry distinct from canonical HOs, generating mycobilin products without releasing carbon monoxide. Its crucial role in the Mtb heme uptake pathway has identified MhuD as an auspicious drug target. MhuD is capable of binding either one or two hemes within a single active site, but only the monoheme form was previously reported to be enzymatically active. Here we employed resonance Raman (rR) spectroscopy to examine several factors proposed to impact the reactivity of mono- and diheme MhuD, including heme ruffling, heme pocket hydrophobicity, and amino acid–heme interactions. We determined that the distal heme in the diheme MhuD active site has negligible effects on both the planarity of the His-coordinated heme macrocycle and the strength of the Fe-N_His linkage relative to the monoheme form. Our rR studies using isotopically labeled hemes unveiled unexpected biomolecular dynamics for the process of heme binding that converts MhuD from mono- to diheme form, where the second incoming heme replaces the first as the His75-coordinated heme. Ferrous CO-ligated diheme MhuD was found to exhibit multiple Fe-C-O conformers, one of which contains catalytically predisposed H-bonding interactions with the distal Asn7 residue identical to those in the monoheme form, implying that it is also enzymatically active. This was substantiated by activity assays and MS product analysis that confirmed the diheme form also degrades heme to mycobilins, redefining MhuD’s functional paradigm and further expanding our understanding of its role in Mtb physiology.

Investigation of Cyanide Ligand as an Active Site Probe of Human Heme Oxygenase

Human heme oxygenase (hHO-1) is a physiologically important enzyme responsible for free heme catabolism. The enzyme's high regiospecificity is controlled by the distal site hydrogen bond network that involves water molecules and the D140 amino acid residue. In this work, we probe the active site environment of the wild-type (WT) hHO-1 and its D140 mutants using resonance Raman (rR) spectroscopy. Cyanide ligands are more stable than dioxygen adducts and are an effective probe of active site environment of heme proteins. The inherently linear geometry of the Fe-C-N fragment can be altered by the steric, electrostatic, and H-bonding interactions imposed by the amino acid residues present in the heme distal site, resulting in a tilted or bent configuration. The WT hHO-1 and its D140A, D140N, and D140E mutants were studied in the presence of natural abundance CN^- and its isotopic analogues (¹³CN^-, C¹⁵N^-, and ¹³C¹⁵N^-). Deconvolution of spectral data revealed that the ν(Fe-CN) stretching and δ(Fe-CN) bending modes are present at 454 and 376 cm^-1, respectively. The rR spectral patterns of the CN^- adducts of WT revealed that the Fe-C-N fragment adopts a tilted conformation, with a larger bending contribution for the D140A, D140N, and D140E mutants. These studies suggest that the FeCN fragment in hHO-1 is tilted more strongly toward the porphyrin macrocycle compared to other histidine-ligated proteins, reflecting the propensity of the exogenous hHO-l ligands to position toward the α-meso-carbon, which is crucial for the HO reactivity and essential for regioselectivity.

Heterologous expression of recombinant urate oxidase using the intein-mediated protein purification in Pichia pastoris

The potential of urate oxidase (uricase) for clinical use has been highlighted because of its role in lowering the blood uric acid levels for the treatment of tumor lysis syndrome. In the present study, the codon-optimized synthetic gene of Aspergillus flavus uricase was fused to the Mxe GyrA intein and chitin-binding domain. The construct was inserted into pPICZA and pPICZαA vectors and electroporated into Pichia pastoris GS115 for the cytosolic and secretory expression. Transformants were screened on gradients of Zeocin up to 2000 μg/ml to find multi-copy integrants. For both constructs, colonies with more resistance were screened for the highest uricase producers by enzyme assay. PCR analysis confirmed successful cassettes insertion into the genome and Mut + phenotype. The gene copy index was determined to be two and five for cytosolic and secretory strains, respectively. Productivity of the cytosolic and secretory strains was found to be 0.74 and 0.001 U/ml culture media in order while the cytosolic recombinant enzyme accounted for about 6% of total proteins. One-step purification of the expressed uricase was done with the aid of the chitin affinity column, followed by DTT induction for intein on-column cleavage. The yield of 40.8 mg/L and K m of 0.22 mM was obtained for intracellular expression. It seems that the intracellular production of uricase can indeed serve as an effective alternative to secretory expression. Moreover, this is the first report considering cytosolic production of uricase using the intein-mediated protein purification in the methylotrophic yeast, P. pastoris.

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.

Chitinase Gene Positively Regulates Hypersensitive and Defense Responses of Pepper to Colletotrichum acutatum Infection

Anthracnose caused by Colletotrichum acutatum is one of the most devastating fungal diseases of pepper (Capsicum annuum L.). The utilization of chitin-binding proteins or chitinase genes is the best option to control this disease. A chitin-binding domain (CBD) has been shown to be crucial for the innate immunity of plants and activates the hypersensitive response (HR). The CaChiIII7 chitinase gene has been identified and isolated from pepper plants. CaChiIII7 has repeated CBDs that encode a chitinase enzyme that is transcriptionally stimulated by C. acutatum infection. The knockdown of CaChiIII7 in pepper plants confers increased hypersensitivity to C. acutatum, resulting in its proliferation in infected leaves and an attenuation of the defense response genes CaPR1, CaPR5, and SAR8.2 in the CaChiIII7-silenced pepper plants. Additionally, H₂O₂ accumulation, conductivity, proline biosynthesis, and root activity were distinctly reduced in CaChiIII7-silenced plants. Subcellular localization analyses indicated that the CaChiIII7 protein is located in the plasma membrane and cytoplasm of plant cells. The transient expression of CaChiIII7 increases the basal resistance to C. acutatum by significantly expressing several defense response genes and the HR in pepper leaves, accompanied by an induction of H₂O₂ biosynthesis. These findings demonstrate that CaChiIII7 plays a prominent role in plant defense in response to pathogen infection.

Structural insights of the enzymes from the chitin utilization locus of Flavobacterium johnsoniae

Chitin is one of the most abundant renewable organic materials found on earth. The chitin utilization locus in Flavobacterium johnsoniae, which encodes necessary proteins for complete enzymatic depolymerization of crystalline chitin, has recently been characterized but no detailed structural information on the enzymes was provided. Here we present protein structures of the F. johnsoniae chitobiase (FjGH20) and chitinase B (FjChiB). FjGH20 is a multi-domain enzyme with a helical domain not before observed in other chitobiases and a domain organization reminiscent of GH84 (β-N-acetylglucosaminidase) family members. The structure of FjChiB reveals that the protein lacks loops and regions associated with exo-acting activity in other chitinases and instead has a more solvent accessible substrate binding cleft, which is consistent with its endo-chitinase activity. Additionally, small angle X-ray scattering data were collected for the internal 70 kDa region that connects the N- and C-terminal chitinase domains of the unique 158 kDa multi-domain chitinase A (FjChiA). The resulting model of the molecular envelope supports bioinformatic predictions of the region comprising six domains, each with similarities to either Fn3-like or Ig-like domains. Taken together, the results provide insights into chitin utilization by F. johnsoniae and reveal structural diversity in bacterial chitin metabolism.

Chitinolytic proteins secreted by Cellulosimicrobium sp. NTK2

Cellulosimicrobium sp. NTK2 (NTK2 strain) was isolated as a chitinolytic bacterium from mature compost derived from chitinous waste. The growth of the NTK2 strain was enhanced by supplementation of the culture medium with 2% crystalline chitin. Approximately 70% of the supplemented crystalline chitin was degraded during cultivation. Whole genome analysis of the NTK2 strain identified eight chitinases and two chitin-binding proteins. The NTK2 strain secreted two bacterial extracellular solute-binding proteins, three family 18 glycosyl hydrolases and one lytic polysaccharide monooxygenase specifically in the presence of crystalline chitin. A chitinolytic enzyme with a molecular mass of 29 kDa on SDS-PAGE under native conditions was also secreted. This chitinolytic enzyme exhibited the largest band upon zymography but could not be identified. In an attempt to identify all the chitinases secreted by the NTK2 strain, we expressed recombinant versions of the proteins exhibiting chitinolytic activity in Escherichia coli. Our results suggest that the 29 kDa protein belonging to family 19 glycosyl hydrolase was expressed specifically in the presence of 2% crystalline chitin.

Regulation of Chitinase in Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) During Infection by Heliothis virescens ascovirus 3h (HvAV-3h)

Insect chitinases play essential roles in the molting and metamorphosis of insects. The virus Heliothis virescens ascovirus 3h (HvAV-3h) can prolong the total duration of the larval stage in its host larvae. In this study, the molecular character and function of chitinase and chitin-binding domain (CBD) were analyzed in larvae of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). In detecting the chitinase activity of mock-infected and HvAV-3h-infected larval whole bodies and four different larval tissues, the results showed that larval chitinase activity was significantly decreased at 48 h post infection (hpi) and that the chitinase activity of HvAV-3h-infected larval fat body and cuticle was notably decreased at 144 and 168 hpi. The transcription level of S. exigua chitinase 7 (SeCHIT7) was down-regulated at the 6, 9, 12, 48, 72, and 96 hpi sample times, the S. exigua chitinase 11 (SeCHIT11) was down-regulated at 3-96 hpi, while both S. exigua chitinases (SeCHITs) were up-regulated at 120-168 hpi. Further tissue-specific detection of SeCHIT7 and SeCHIT11 transcription showed that SeCHIT7 was down-regulated at 144 and 168 hpi in the fat body and cuticle. SeCHIT11 was down-regulated at 168 hpi in the fat body, midgut, and cuticle. Additionally, the transcription and expression of S. exigua chitin-binding domain (SeCBD) could not be detected in HvAV-3h-infected larvae. The in vitro analyses of SeCHIT7N, SeCHIT11, and SeCBD showed that SeCHIT7N and SeCHIT11 were typical chitinases. Conversely, no chitinase activity was detected with SeCBD. SeCBD, however, could significantly increase the activity of SeCHIT7N and SeCHIT11. In conclusion, HvAV-3h not only interfered with the transcription and expression of SeCHITs but also affected the normal transcription and expression of SeCBD and, in doing so, influenced the host larval chitinase activity. These results will aid in providing a foundation for further studies on the pathogenesis of HvAV-3h.

Uniform spheroid formation on a laboratory-made, low cell attachment surface consisting of a chitin sheet

We utilized the reaction of chitosan with acetic anhydride to form a chitin gel. This gel was then dried, which formed a chitin sheet. The procedure was extremely easy for a biologist unfamiliar with materials engineering. Spheroids derived from HEK293T cells were formed on the chitin sheet, because the spheroids slightly attached and slowly moved on the chitin sheet.

Chitinases of Bacillus thuringiensis: Phylogeny, Modular Structure, and Applied Potentials

The most important bioinsecticide used worldwide is Bacillus thuringiensis and its hallmark is a rich variety of insecticidal Cry protein, many of which have been genetically engineered for expression in transgenic crops. Over the past 20 years, the discovery of other insecticidal proteins and metabolites synthesized by B. thuringiensis, including chitinases, antimicrobial peptides, vegetative insecticidal proteins (VIP), and siderophores, has expanded the applied value of this bacterium for use as an antibacterial, fungicidal, and nematicidal resource. These properties allow us to view B. thuringiensis not only as an entity for the production of a particular metabolite, but also as a multifaceted microbial factory. In particular, chitinases of B. thuringiensis are secreted enzymes that hydrolyze chitin, an abundant molecule in the biosphere, second only to cellulose. The observation that chitinases increase the insecticidal activity of Cry proteins has stimulated further study of these enzymes produced by B. thuringiensis. Here, we provide a review of a subset of our knowledge of B. thuringiensis chitinases as it relates to their phylogenetic relationships, regulation of expression, biotechnological potential for controlling entomopathogens, fungi, and nematodes, and their use in generating chitin-derived oligosaccharides (ChOGs) that possess antibacterial activities against a number of clinically significant bacterial pathogens. Recent advances in the structural organization of these enzymes are also discussed, as are our perspective for future studies.

Truncated Thioredoxin Peptides Serves as an Efficient Fusion Tag for Production of Proinsulin

BACKGROUND

Insulin is a peptide hormone used for regulating blood glucose levels. Human insulin market is projected to grow at a rate of 12.5% annually. To meet the needs of patients, a cost effective insulin manufacturing strategy has to be developed. This can be achieved by selecting a competent host, ideal fusion tag and streamlined downstream process.

OBJECTIVE

In this article, we have demonstrated that selecting a right fusion partner for expression of toxic proteins like insulin, plays a major role in increasing the recombinant protein yield.

METHODS

In this article, we have focused on identifying a peptide tag fusion partner for expressing proinsulin by truncating thioredoxin tag. Truncations were carried out from both Amino and Carboxy terminus of the protein and efficiency of truncated sequences was evaluated by expressing it with proinsulin gene. FCTRX (1-15) sequence fused to proinsulin was processed further to establish downstream protocol for purification.

RESULTS

Thioredoxin tag was truncated appropriately by considering the fusion tag: protein ratio. A couple of sequences ranging 10 - 15 amino acids were identified based on its in silico properties. Of these FCTRX (1-15) showed increased expression and stability of fusion protein. 156 mg of purified insulin was generated from 1g of inclusion body after enzymatic conversion and chromatographic steps.

CONCLUSION

As a result of the current study, it was concluded that FCTRX (1-15) peptide has advantageous attributes to be considered as an ideal fusion tag for expression of proinsulin. This can be further explored by expressing it with other proteins.

"Fishing and Hunting"-Selective Immobilization of a Recombinant Phenylalanine Ammonia-Lyase from Fermentation Media

This article overviews the numerous immobilization methods available for various biocatalysts such as whole-cells, cell fragments, lysates or enzymes which do not require preliminary enzyme purification and introduces an advanced approach avoiding the costly and time consuming downstream processes required by immobilization of purified enzyme-based biocatalysts (such as enzyme purification by chromatographic methods and dialysis). Our approach is based on silica shell coated magnetic nanoparticles as solid carriers decorated with mixed functions having either coordinative binding ability (a metal ion complexed by a chelator anchored to the surface) or covalent bond-forming ability (an epoxide attached to the surface via a proper linker) enabling a single operation enrichment and immobilization of a recombinant phenylalanine ammonia-lyase from parsley fused to a polyhistidine affinity tag.

Chitin degradation enzyme-responsive system for controlled release of fibroblast growth factor-2

Chitin is widely found in fungal cell walls and arthropod exoskeletons, and is used as a biomedical material. However, chitin is not water-soluble, restricting its use for controlled release materials. We found that water-soluble chitosan can be acetylated to produce a chitin equivalent, or chitin gel. Chitin gel, produced by mixing chitosan solution with acetic anhydride, can be degraded by lysozyme and fetal bovine serum, so could provide an ideal means for controlled release in biological systems. We tested a combination of chitin gel with a chitin binding domain (CBD) fusion protein as a controlled release system regulated by chitin degradation. A fusion protein consisting of fibroblast growth factor 2 (FGF-2) fused to CBD bound the chitin gel, and was released time-dependently rather than as an initial burst during lysozyme degradation, suggesting that this system could provide a means for controlled drug release in biological systems. Contrastingly, the trinitrophenyl residue (TNP-X) covalently bound to chitin gel, and was released by lysozyme degradation with an initial burst. If release of CBD-FGF-2 were simply dependent on lysozyme degradation of the chitin gel, the release behavior of CBD-FGF-2 would be similar to that of TNP-X, with an initial burst. Therefore, we propose that CBD-FGF-2 repeats the cycle of binding, release, and re-binding to the chitin gel during degradation. This system allows for a time-dependent, controlled release of CBD-FGF-2 without an initial burst.

Molecular and Biochemical Characterization of a Bimodular Xylanase From Marinifilaceae Bacterium Strain SPP2

In this study, the first xylantic enzyme from the family Marinifilaceae, XynSPP2, was identified from Marinifilaceae bacterium strain SPP2. Amino acid sequence analysis revealed that XynSPP2 is a rare Fn3-fused xylanase, consisting of a signal peptide, a fibronectin type-III domain (Fn3), and a C-terminal catalytic domain belonging to glycoside hydrolase family 10 (GH10). The catalytic domain shared 17–46% identities to those of biochemically characterized GH10 xylanases. Structural analysis revealed that the conserved asparagine and glutamine at the glycone −2/−3 subsite of GH10 xylanases are substituted by a tryptophan and a serine, respectively, in XynSPP2. Full-length XynSPP2 and its Fn3-deleted variant (XynSPP2ΔFn3) were overexpressed in Escherichia coli and purified by Ni-affinity chromatography. The optimum temperature and pH for both recombinant enzymes were 50°C and 6, respectively. The enzymes were stable under alkaline condition and at temperature lower than 50°C. With beechwood xylan as the substrate, XynSPP2 showed 2.8 times the catalytic efficiency of XynSPP2ΔFn3, indicating that the Fn3 module promotes xylanase activity. XynSPP2 was active toward xylooligosaccharides (XOSs) longer than xylotriose. Such a substrate preference can be explained by the unique −2/−3 subsite composition in the enzyme which provides new insight into subsite interaction within the GH10 family. XynSPP2 hydrolyzed beechwood xylan into small XOSs (xylotriose and xylotetraose as major products). No monosaccharide was detected by thin-layer chromatography which may be ascribed to putative transxylosylation activity of XynSPP2. Preferring long XOS substrate and lack of monosaccharide production suggest its potential in probiotic XOS manufacture.

Identification of an endo-chitinase from Corallococcus sp. EGB and evaluation of its antifungal properties

As the main component of the fungal cell wall, chitin has been regarded as an optimal molecular target for the biocontrol of plant-pathogenic fungi. In this study, the chitin hydrolase CcCti1, which belongs to the glycoside hydrolase family 18 (GH 18) and exhibits potential antifungal activity, was identified from Corallococcus sp. EGB. CcCti1 lacks a fibronectin type-III (FN3) domain that is present in similar enzymes from most genera of myxobacteria, indicating that CcCti1 may have acquired chitinase activity due to the FN3 domain deletion during myxobacterial evolution. CcCti1 was expressed in Escherichia coli BL21 (DE3) with a specific activity of up to 10.5 U/μmol with colloidal chitin as the substrate. Product analysis showed that CcCti1 could hydrolyze chitin into N-acetylated chitohexaose (GlcNAc)₆ as the major product, in addition to chitooligosaccharides. The analysis of biochemical properties indicated that the CBD and FN3 domains in CcCti1 determine the substrate affinity and pH stability. Otherwise, CcCti1 exhibited efficient biocontrol activity against the plant pathogen Magnaporthe oryzae in a dose-dependent manner, inhibiting the conidia germination and appressoria formation at a concentration of 0.08 mg/mL. Overall, the chitohexaose-producing chitinase CcCti1 with hydrolytic features may find potential application in chitin conversion and biocontrol of fungal plant diseases.

Scalable Geometrically Designed Protein Cages Assembled via Genetically Encoded Split Inteins

Engineering proteins to assemble into user-defined structures is key in their development for biotechnological applications. However, designing generic rather than bespoke solutions is challenging. Here we describe an expandable recombinant assembly system that produces scalable protein cages via split intein-mediated native chemical ligation. Three types of component are used: two complementary oligomeric "half-cage" protein fusions and an extendable monomeric "linker" fusion. All are composed of modular protein domains chosen to fulfill the required geometries, with two orthogonal pairs of split intein halves to drive assembly when mixed. This combination enables both one-pot construction of two-component cages and stepwise assembly of larger three-component scalable cages. To illustrate the system's versatility, trimeric half-cages and linker constructs comprising consensus-designed repeat proteins were ligated in one-pot and stepwise reactions. Under mild conditions, rapid high-yielding ligations were obtained, from which discrete proteins cages were easily purified and shown to form the desired trigonal bipyramidal structures.

The crystal structure of the chitinase ChiA74 of Bacillus thuringiensis has a multidomain assembly

There is no structural information about any chitinase synthesized by Bacillus thuringiensis, the most successful microbial insect larvicide used worldwide. In this study, we solved the 3D structure of the chitinase ChiA74 at 2.26 Å. The crystal structure shows that ChiA74 is composed of a modular arrangement formed by (i) a catalytic region (CD), (ii) a chitinase insertion domain (CID), (iii) a fibronectin type III domain (FnIII), and (iv) a chitin binding domain (CBD). The location of the CBD with respect to the CD has no structural similarity to other chitinases with known structures. The activity of a ChiA74 lacking its secretion signal peptide (ChiA74Δsp) and a truncated version lacking its CBD/FnIII domains (ChiA74Δsp-50) did not have statistical differences in activity against colloidal chitin. However, ChiA74Δsp exhibits 4.5 and 2.0 higher activity than versions lacking the CBD (ChiA74Δsp-60) and CBD/FnIII domains (ChiA74Δsp-50), respectively, when crystalline chitin was used as substrate. Our data suggest that the CBD might plays a significant role in crystalline chitin hydrolysis. We also demonstrated the importance of the catalytic E211 in the CD, as mutants ChiA74Δsp_E211N and ChiA74Δsp_{D207N, E211N} were inactive against colloidal and crystalline chitins, chitosan and 4-MU-GlcNAc₃. ChiA74 has a processive activity producing oligosaccharides with degree of polymerization (DP) of 1 (GlcNAc) and 2 (GlcNAc₂).

The Listeria innocua chitinase LinChi78 has a unique region that is necessary for hydrolytic activity

Chitinases are generally composed of multiple domains; a catalytic domain and one or more additional domains that are not absolutely required but may modify the chitinolytic activity. The LinChi78 chitinase from Listeria innocua has a catalytic domain (CatD), a fibronectin type III-like (FnIII) domain, a chitin-binding domain (ChBD), and an unknown-function region (UFR) located between the CatD and FnIII domains. The UFR is 146 amino acid residues in length and does not have a homologous domain in the Conserved Domain Database. We performed a functional analysis of these domains and the UFR using several C-terminally and internally deleted mutants of LinChi78. Hydrolysis of an artificial substrate was almost unaffected by deletion of the ChBD and/or the FnIII domain, although the ChBD-deleted enzymes were approximately 30% less active toward colloidal chitin than LinChi78. On the other hand, deletion of the UFR led to an extensive loss of chitinase activity toward an artificial substrate as well as polymeric substrates. Upon further analysis, we found that the GKQTI stretch, between the 567th (G) and 571th (I) amino acid residues, in the UFR is critical for LinChi78 activity and demonstrated that Gln569 and Ile571 play central roles in eliciting this activity. Taken together, these results indicated that LinChi78 has a unique catalytic region composed of a typical CatD and an additional region that is essential for activity. Characterization of the unique catalytic region of LinChi78 will improve our understanding of GH18 chitinases.

Bacterial Chitinase System as a Model of Chitin Biodegradation

Chitin, a structural polysaccharide of β-1,4-linked N-acetyl-D-glucosamine residues, is the second most abundant natural biopolymer after cellulose. The metabolism of chitin affects the global carbon and nitrogen cycles, which are maintained by marine and soil-dwelling bacteria. The degradation products of chitin metabolism serve as important nutrient sources for the chitinolytic bacteria. Chitinolytic bacteria have elaborate enzymatic systems for the degradation of the recalcitrant chitin biopolymer. This chapter introduces chitin degradation and utilization systems of the chitinolytic bacteria. These bacteria secrete many chitin-degrading enzymes, including processive chitinases, endo-acting non-processive chitinases, lytic polysaccharide monooxygenases, and N-acetyl-hexosaminidases. Bacterial chitinases play a fundamental role in the degradation of chitin. Enzymatic properties, catalytic mechanisms, and three-dimensional structures of chitinases have been extensively studied by many scientists. These enzymes can be exploited to produce a range of chitin-derived products, e.g., biocontrol agents against many plant pathogenic fungi and insects. We introduce bacterial chitinases in terms of their reaction modes and structural features.

Deletion of uncharacterized domain from α-1,3-glucanase of Bacillus circulans KA-304 enhances heterologous enzyme production in Escherichia coli

α-1,3-Glucanase (Agl-KA) of Bacillus circulans KA-304 consists of an N-terminal discoidin domain (DS1), a carbohydrate binding module family 6 (CBM6), threonine and proline repeats (TP), a second discoidin domain (DS2), an uncharacterized conserved domain (UCD), and a C-terminal catalytic domain. Previously, we reported that DS1, CBM6, and DS2 have α-1,3-glucan-binding activity and contribute to α-1,3-glucan hydrolysis. In this study, UCD deletion mutant (AglΔUCD) was constructed, and its properties were compared with those of Agl-KA. α-1,3-Glucan hydrolyzing, α-1,3-glucan binding, and protoplast-forming activities of AglΔUCD were almost the same as those of Agl-KA. k_cat/K_m values of AgΔUCD and Agl-KA were 11.4 and 11.1 s^-1 mg^-1 mL, respectively. AglΔUCD and Agl-KA exhibited similar characteristics, such as optimal pH, pH stability, optimal temperature, and thermostability. These results suggest that UCD is not α-1,3-glucan-binding and flexible linker domain, and that deletion of UCD does not affect the affinity of N-terminal binding domains and the catalytic action of the C-terminal domain. Subsequently, heterologous UCenzyme productivity of AglΔD in Escherichia coli was compared with that of Agl-KA. The productivity of AglΔUCD was about 4-fold larger than that of Agl-KA after an 8-h induction at 30°C. In the case of induction at 20°C, the productivity of AglΔUCD was also larger than that of Agl-KA. These findings indicate that deletion of only UCD enhances the enzyme productivity in E. coli.

Chitin-based barrier immunity and its loss predated mucus-colonization by indigenous gut microbiota

Mammalian gut microbiota are integral to host health. However, how this association began remains unclear. We show that in basal chordates the gut space is radially compartmentalized into a luminal part where food microbes pass and an almost axenic peripheral part, defined by membranous delamination of the gut epithelium. While this membrane, framed with chitin nanofibers, structurally resembles invertebrate peritrophic membranes, proteome supports its affinity to mammalian mucus layers, where gut microbiota colonize. In ray-finned fish, intestines harbor indigenous microbes, but chitinous membranes segregate these luminal microbes from the surrounding mucus layer. These data suggest that chitin-based barrier immunity is an ancient system, the loss of which, at least in mammals, provided mucus layers as a novel niche for microbial colonization. These findings provide a missing link for intestinal immune systems in animals, revealing disparate mucosal environment in model organisms and highlighting the loss of a proven system as innovation.

The coevolution of the animal gut mucosa and the gut microbiota is poorly understood. Here, Nakashima et al. identify intestinal chitinous membranes in basal chordates and ray-finned fish, and propose that the loss of this chitin barrier allowed mucus layers to become colonized by microbes in mammals.

C-Terminal sequence is involved in the incorporation of Bgl2p glucanosyltransglycosylase in the cell wall of Saccharomyces cerevisiae

A cell wall (CW) provides a protective barrier for a yeast cell and is a firm structure that nevertheless dynamically changes during cell's growth. Bgl2p is a non-covalently anchored glucanosyltransglycosylase in the CW of the yeast Saccharomyces cerevisiae. The mode of its anchorage is poorly understood, while its association with CW components is tight and resistant to 1-h treatment with 1% SDS at 37°C. In order to demarcate the potential structural block responsible for incorporation of Bgl2p into the CW, bioinformatics analysis of its sequence was performed, and a conservative structural region was identified in the C-terminal region of Bgl2p, which was absent in its homologues in S. cerevisiae, the Scw4p and Scw10p. Deletion of this region disrupted the incorporation of Bgl2p into the CW and led to release of this protein through the CW into the culture medium. Two left-handed polyproline-II helices were identified in the C-terminal region of the structure model of a wild-type Bgl2p. These helices potentially formed binding sites, which were absent in the truncated protein. Using immune fluorescence microscopy, we demonstrated that C-truncated Bgl2p was exported into culture medium and lost its ability to form fibrils described earlier. It was also shown that the C-terminal truncation of Bgl2p led to a more severe decrease of cell survivability in extreme conditions than BGL2 deletion.

Rapid determination of binding parameters of chitin binding domains using chitin-coated quartz crystal microbalance sensor chips

Chitin present in fungal cell walls has been considered as a diagnostic polymer for the detection of fungal infections.

Characterization of a Bacillus thuringiensis chitinase that binds to cellulose and chitin

Bacillus thuringiensis is a Gram-positive soil bacterium that is known to be a bacterial biopesticide that produces insecticidal proteins called crystal proteins (Cry). In the insecticidal process, chitinases are suggested to perforate the peritrophic membrane barrier to facilitate the invasion of the Cry proteins into epithelial membranes. A chitinase gene from B. thuringiensis was successfully expressed in a soluble form in Escherichia coli, and the gene product was purified and characterized. The purified recombinant enzyme, BthChi74, hydrolyzed an artificial substrate, 4-nitrophenyl N,N′-diacetyl-β-d-chitobioside [4NP-(GlcNAc)₂], and the natural substrates, colloidal chitin and crystalline α-chitin, but it did not hydrolyze cellulose. BthChi74 exhibited catalytic activity under a weakly acidic to neutral pH range at 50 °C, and it was stable over a wide pH range for 24 h. Differential scanning fluorimetry (DSF) indicated a protein melting temperature (T_m) of 63.6 °C. Kinetic analysis revealed k_cat and K_M values of 1.5 s⁻¹ and 159 μM, respectively, with 4NP-(GlcNAc)₂ as a substrate. BthChi74 produced (GlcNAc)₂ and GlcNAc from colloidal chitin and α-chitin as substrates, but the activity toward the latter was lower than that toward the former. BthChi74 could bind similarly to chitin beads, crystalline α-chitin, and cellulose through a unique family 2 carbohydrate-binding module (CBM2). The structure–function relationships of BthChi74 are discussed in relation to other chitinases, such as Listeria chitinase, which possesses a family 5 carbohydrate-binding module (CBM5).

A case study of Desmozoon lepeophtherii infection in farmed Atlantic salmon associated with gill disease, peritonitis, intestinal infection, stunted growth, and increased mortality

Background

In September 2008, a disease outbreak characterized by acute, severe gill pathology and peritonitis, involving the gastrointestinal tract, was observed in an Atlantic salmon (Salmo salar L.) farm in north-western Norway. During subsequent sampling in November 2008 and January 2009, chronic proliferative gill inflammation and peritonitis was observed. Cumulative mortalities of 5.6–12.8% and severe growth retardation were observed. Routine diagnostic analysis revealed no diseases known to salmon at the time, but microsporidian infection of tissues was observed.

Methods

To characterize the disease outbreak, a combination of histopathology, in situ hybridization (ISH), chitin, calcofluor-white (CFW) staining, and real-time PCR were used to describe the disease progression with visualization of the D. lepeophtherii stages in situ.

Results

The presence of the microsporidian Desmozoon lepeophtherii was confirmed with real-time PCR, DNA sequencing and ISH, and the parasite was detected in association with acute lesions in the gills and peritoneum. ISH using a probe specific to small subunit 16S rRNA gene provided an effective tool for demonstrating the distribution of D. lepeophtherii in the tissue. Infection in the peritoneum seemed localized in and around pre-existing vaccine granulomas, and in the gastrointestinal walls. In the heart, kidney and spleen, the infection was most often associated with mononuclear leucocytes and macrophages, including melanomacrophages. Desmozoon lepeophtherii exospores were found in the nuclei of the gastrointestinal epithelium for the first time, suggesting a role of the gastrointestinal tract in the spread of spores to the environment.

Conclusions

This study describes the progression of D. lepeophtherii disease outbreak in an Atlantic salmon farm without any other known diseases present. Using different methods to examine the disease outbreak, new insight into the pathology of D. lepeophtherii was obtained. The parasite was localized in situ in association with severe tissue damage and inflammation in the gills, peritoneal cavity and in the gastrointestinal (GI) tract that links the parasite directly to the observed pathology.

In silico analysis of ChtBD3 domain to find its role in bacterial pathogenesis and beyond

Chitin binding domain 3, known by the acronym ChtBD3, is a domain in the enzymes and proteins of several pathogenic virus, bacteria and fungi. As this domain is evolutionarily-conserved in virulence factors of these infectious agents, its detailed investigation is of clinical interest. In this regard, the current in silico study analyzed ChtBD3 domain distribution in bacterial proteins present in publicly-available SMART (simple modular architecture research tool) database. Also, the co-occurring domains of ChtBD3 in the studied proteins were mapped to understand positional rearrangement of the domain and consequent functional diversity. Custom-made scripts were used to interpret the data and to derive patterns. As expected, interesting results were obtained. ChtBD3 domain co-occurred with other critical domains like peptidase, glycol_hydrolase, kinase, hemagglutinin-acting, collagen-binding, among others. The findings are expected to be of clinical relevance.

Characterization of N-Acetylglucosamine Biosynthesis in Pneumocystis species. A New Potential Target for Therapy

N-acetylglucosamine (GlcNAc) serves as an essential structural sugar on the cell surface of organisms. For example, GlcNAc is a major component of bacterial peptidoglycan, it is an important building block of fungal cell walls, including a major constituent of chitin and mannoproteins, and it is also required for extracellular matrix generation by animal cells. Herein, we provide evidence for a uridine diphospho (UDP)-GlcNAc pathway in Pneumocystis species. Using an in silico search of the Pneumocystis jirovecii and P. murina (Pm) genomic databases, we determined the presence of at least four proteins implicated in the Saccharomyces cerevisiae UDP-GlcNAc biosynthetic pathway. These genes, termed GFA1, GNA1, AGM1, and UDP-GlcNAc pyrophosphorylase (UAP1), were either confirmed to be present in the Pneumocystis genomes by PCR, or, in the case of Pm uap1 (Pmuap1), functionally confirmed by direct enzymatic activity assay. Expression analysis using quantitative PCR of Pneumocystis pneumonia in mice demonstrated abundant expression of the Pm uap1 transcript. A GlcNAc-binding recombinant protein and a novel GlcNAc-binding immune detection method both verified the presence of GlcNAc in P. carinii (Pc) lysates. Studies of Pc cell wall fractions using high-performance gas chromatography/mass spectrometry documented the presence of GlcNAc glycosyl residues. Pc was shown to synthesize GlcNAc in vitro. The competitive UDP-GlcNAc substrate synthetic inhibitor, nikkomycin Z, suppressed incorporation of GlcNAc by Pc preparations. Finally, treatment of rats with Pneumocystis pneumonia using nikkomycin Z significantly reduced organism burdens. Taken together, these data support an important role for GlcNAc generation in the cell surface of Pneumocystis organisms.

Spontaneous Chitin Accumulation in Airways and Age-Related Fibrotic Lung Disease

The environmentally widespread polysaccharide chitin is degraded and recycled by ubiquitous bacterial and fungal chitinases. Although vertebrates express active chitinases from evolutionarily conserved loci, their role in mammalian physiology is unclear. We show that distinct lung epithelial cells secrete acidic mammalian chitinase (AMCase), which is required for airway chitinase activity. AMCase-deficient mice exhibit premature morbidity and mortality, concomitant with accumulation of environmentally derived chitin polymers in the airways and expression of pro-fibrotic cytokines. Over time, these mice develop spontaneous pulmonary fibrosis, which is ameliorated by restoration of lung chitinase activity by genetic or therapeutic approaches. AMCase-deficient epithelial cells express fibrosis-associated gene sets linked with cell stress pathways. Mice with lung fibrosis due to telomere dysfunction and humans with interstitial lung disease also accumulate excess chitin polymers in their airways. These data suggest that altered chitin clearance could exacerbate fibrogenic pathways in the setting of lung diseases characterized by epithelial cell dysfunction.

Purification and Characterization of a Major Extracellular Chitinase from a Biocontrol Bacterium, Paenibacillus elgii HOA73

Chitinase-producing Paenibacillus elgii strain HOA73 has been used to control plant diseases. However, the antimicrobial activity of its extracellular chitinase has not been fully elucidated. The major extracellular chitinase gene (PeChi68) from strain HOA73 was cloned and expressed in Escherichia coli in this study. This gene had an open reading frame of 2,028 bp, encoding a protein of 675 amino acid residues containing a secretion signal peptide, a chitin-binding domain, two fibronectin type III domains, and a catalytic hydrolase domain. The chitinase (PeChi68) purified from recombinant E. coli exhibited a molecular mass of approximately 68 kDa on SDS-PAGE. Biochemical analysis indicated that optimum temperature for the actitvity of purified chitinase was 50ºC. However, it was inactivated with time when it was incubated at 40ºC and 50ºC. Its optimum activity was found at pH 7, although its activity was stable when incubated between pH 3 and pH 11. Heavy metals inhibited this chitinase. This purified chitinase completely inhibited spore germination of two Cladosporium isolates and partially inhibited germination of Botrytis cinerea spores. However, it had no effect on the spores of a Colletotricum isolate. These results indicate that the extracellular chitinase produced by P. elgii HOA73 might have function in limiting spore germination of certain fungal pathogens.

A chitinase is required for Xylella fastidiosa colonization of its insect and plant hosts

Xylella fastidiosa colonizes the xylem network of host plant species as well as the foregut of its required insect vectors to ensure efficient propagation. Disease management strategies remain inefficient due to a limited comprehension of the mechanisms governing both insect and plant colonization. It was previously shown that X. fastidiosa has a functional chitinase (ChiA), and that chitin likely serves as a carbon source for this bacterium. We expand on that research, showing that a chiA mutant strain is unable to grow on chitin as the sole carbon source. Quantitative PCR assays allowed us to detect bacterial cells in the foregut of vectors after pathogen acquisition; populations of the wild-type and complemented mutant strain were both significantly larger than the chiA mutant strain 10 days, but not 3 days, post acquisition. These results indicate that adhesion of the chiA mutant strain to vectors may not be impaired, but that cell multiplication is limited. The mutant was also affected in its transmission by vectors to plants. In addition, the chiA mutant strain was unable to colonize host plants, suggesting that the enzyme has other substrates associated with plant colonization. Lastly, ChiA requires other X. fastidiosa protein(s) for its in vitro chitinolytic activity. The observation that the chiA mutant strain is not able to colonize plants warrants future attention to be paid to the substrates for this enzyme.

Characterization of two novel bacterial type A exo-chitobiose hydrolases having C-terminal 5/12-type carbohydrate-binding modules

Type A chitinases (EC 3.2.1.14), GH family 18, attack chitin ((1 → 4)-2-acetamido-2-deoxy-β-D-glucan) and chito-oligosaccharides from the reducing end to catalyze release of chitobiose (N,N'-diacetylchitobiose) via hydrolytic cleavage of N-acetyl-β-D-glucosaminide (1 → 4)-β-linkages and are thus "exo-chitobiose hydrolases." In this study, the chitinase type A from Serratia marcescens (SmaChiA) was used as a template for identifying two novel exo-chitobiose hydrolase type A enzymes, FbalChi18A and MvarChi18A, originating from the marine organisms Ferrimonas balearica and Microbulbifer variabilis, respectively. Both FbalChi18A and MvarChi18A were recombinantly expressed in Escherichia coli and were confirmed to exert exo-chitobiose hydrolase activity on chito-oligosaccharides, but differed in temperature and pH activity response profiles. Amino acid sequence comparison of the catalytic β/α barrel domain of each of the new enzymes showed individual differences, but ~69% identity of each to that of SmaChiA and highly conserved active site residues. Superposition of a model substrate on 3D structural models of the catalytic domain of the enzymes corroborated exo-chitobiose hydrolase type A activity for FbalChi18A and MvarChi18A, i.e., substrate attack from the reducing end. A main feature of both of the new enzymes was the presence of C-terminal 5/12 type carbohydrate-binding modules (SmaChiA has no C-terminal carbohydrate binding module). These new enzymes may be useful tools for utilization of chitin as an N-acetylglucosamine donor substrate via chitobiose.

Chitin and chitinase: Role in pathogenicity, allergenicity and health

Chitin, a polysaccharide with particular abundance in fungi, nematodes and arthropods is immunogenic. It acts as a threat to other organisms, to tackle which they have been endowed with chitinase enzyme. Even if this enzyme is not present in all organisms, they possess proteins having chitin-binding domain(s) (ChtBD). Many lethal viruses like Ebola, and HCV (Hepatitis C virus) have these domains to manipulate their carriers and target organisms. In keeping with the basic rule of survival, the self-origin (own body component) chitins and chitinases are protective, but that of non-self origin (from other organisms) are detrimental to health. The exogenous chitins and chitinases provoke human innate immunity to generate a deluge of inflammatory cytokines, which injure organs (leading to asthma, atopic dermatitis etc.), and in persistent situations lead to death (multiple sclerosis, systemic lupus erythromatosus (SLE), cancer, etc.). Unfortunately, chitin-chitinase-stimulated hypersensitivity is a common cause of occupational allergy. On the other hand, chitin, and its deacetylated derivative chitosan are increasingly proving useful in pharmaceutical, agriculture, and biocontrol applications. This critical review discusses the complex nexus of chitin and chitinase and assesses both their pathogenic as well as utilitarian aspects.

Mechanical Control of Whole Body Shape by a Single Cuticular Protein Obstructor-E in Drosophila melanogaster

Body shapes are much more variable than body plans. One way to alter body shapes independently of body plans would be to mechanically deform bodies. To what extent body shapes are regulated physically, or molecules involved in physical control of morphogenesis, remain elusive. During fly metamorphosis, the cuticle (exoskeleton) covering the larval body contracts longitudinally and expands laterally to become the ellipsoidal pupal case (puparium). Here we show that Drosophila melanogaster Obstructor-E (Obst-E) is a protein constituent of the larval cuticle that confers the oriented contractility/expandability. In the absence of obst-E function, the larval cuticle fails to undergo metamorphic shape change and finally becomes a twiggy puparium. We present results indicating that Obst-E regulates the arrangement of chitin, a long-chain polysaccharide and a central component of the insect cuticle, and directs the formation of supracellular ridges on the larval cuticle. We further show that Obst-E is locally required for the oriented shape change of the cuticle during metamorphosis, which is associated with changes in the morphology of those ridges. Thus, Obst-E dramatically affects the body shape in a direct, physical manner by controlling the mechanical property of the exoskeleton.

Shapes of objects, living or not, should depend on their material properties and forces acting on them. Mechanical processes that create whole body shapes of multicellular organisms, or genes that regulate such processes, are largely unknown. Insect bodies are coated by cuticle, a matrix composed of proteins and the polysaccharide chitin. We show that, during metamorphosis of the fruit fly Drosophila melanogaster, the cuticle covering the long and thin larva (maggot) undergoes longitudinal contraction and lateral expansion to become the short and stout puparium covering the pupa. Furthermore, we identify a single protein component of the larval cuticle that confers the oriented contractility/expandability, thereby determining the pupal body shape in a mechanical manner.

Biological Potential of Chitinolytic Marine Bacteria

Chitinolytic microorganisms secrete a range of chitin modifying enzymes, which can be exploited for production of chitin derived products or as fungal or pest control agents. Here, we explored the potential of 11 marine bacteria (Pseudoalteromonadaceae, Vibrionaceae) for chitin degradation using in silico and phenotypic assays. Of 10 chitinolytic strains, three strains, Photobacterium galatheae S2753, Pseudoalteromonas piscicida S2040 and S2724, produced large clearing zones on chitin plates. All strains were antifungal, but against different fungal targets. One strain, Pseudoalteromonas piscicida S2040, had a pronounced antifungal activity against all seven fungal strains. There was no correlation between the number of chitin modifying enzymes as found by genome mining and the chitin degrading activity as measured by size of clearing zones on chitin agar. Based on in silico and in vitro analyses, we cloned and expressed two ChiA-like chitinases from the two most potent candidates to exemplify the industrial potential.