X-ray structure and mutagenesis analyses of Clostridioides difficile endolysin Ecd09610 glucosaminidase domain.

Clostridioides difficile endolysin (Ecd09610) consists of an unknown domain at its N terminus, followed by two catalytic domains, a glucosaminidase domain and endopeptidase domain. X-ray structure and mutagenesis analyses of the Ecd09610 catalytic domain with glucosaminidase activity (Ecd09610CD53) were performed. Ecd09610CD53 was found to possess an α-bundle-like structure with nine helices, which is well conserved among GH73 family enzymes. The mutagenesis analysis based on X-ray structures showed that Glu405 and Asn470 were essential for enzymatic activity. Ecd09610CD53 may adopt a neighboring-group mechanism for a catalytic reaction in which Glu405 acted as an acid/base catalyst and Asn470 helped to stabilize the oxazolinium ion intermediate. Structural comparisons with the newly identified Clostridium perfringens autolysin catalytic domain (AcpCD) in the P1 form and a zymography analysis demonstrated that AcpCD was 15-fold more active than Ecd09610CD53. The strength of the glucosaminidase activity of the GH73 family appears to be dependent on the depth of the substrate-binding groove.

Functionally modified chitotriosidase catalytic domain for chitin detection based on split-luciferase complementation.

In this study, we applied a luciferase-fragment complementation assay for chitin detection. When luciferase-fragment fused chitin-binding proteins were mixed with chitin, the reconstituted luciferase became active. The recombinant chitin-binding domain (CBD) and a functionally modified catalytic domain (CatD) of human chitotriosidase were employed for this method. We designed the CatD mutant as a chitin-binding protein with diminished chitinolytic activity. The non-wash assay using the CatD mutant had higher sensitivity than CBD for chitin detection and proved to be a structure-specific biosensor for chitin, including crude biomolecules (from fungi, mites, and cockroaches). The CatD mutant recognized a chitin-tetramer as the minimal binding unit and bound chitin at KD 99 nM. Furthermore, a sandwich ELISA using modified CatD showed a low limit of quantification for soluble chitin (13.6 pg/mL). Altogether, our work shows a reliable method for chitin detection using the potential capabilities of CatD.

Discovery of Octahydroisoindolone as a Scaffold for the Selective Inhibition of Chitinase B1 from Aspergillus fumigatus: In Silico Drug Design Studies.

Chitinases represent an alternative therapeutic target for opportunistic invasive mycosis since they are necessary for fungal cell wall remodeling. This study presents the design of new chitinase inhibitors from a known hydrolysis intermediate. Firstly, a bioinformatic analysis of Aspergillus fumigatus chitinase B1 (AfChiB1) and chitotriosidase (CHIT1) by length and conservation was done to obtain consensus sequences, and molecular homology models of fungi and human chitinases were built to determine their structural differences. We explored the octahydroisoindolone scaffold as a potential new antifungal series by means of its structural and electronic features. Therefore, we evaluated several synthesis-safe octahydroisoindolone derivatives by molecular docking and evaluated their AfChiB1 interaction profile. Additionally, compounds with the best interaction profile (1-5) were docked within the CHIT1 catalytic site to evaluate their selectivity over AfChiB1. Furthermore, we considered the interaction energy (MolDock score) and a lipophilic parameter (aLogP) for the selection of the best candidates. Based on these descriptors, we constructed a mathematical model for the IC50 prediction of our candidates (60-200 µM), using experimental known inhibitors of AfChiB1. As a final step, ADME characteristics were obtained for all the candidates, showing that 5 is our best designed hit, which possesses the best pharmacodynamic and pharmacokinetic character.

Prominent members of the human gut microbiota express endo-acting O-glycanases to initiate mucin breakdown.

The thick mucus layer of the gut provides a barrier to infiltration of the underlying epithelia by both the normal microbiota and enteric pathogens. Some members of the microbiota utilise mucin glycoproteins as a nutrient source, but a detailed understanding of the mechanisms used to breakdown these complex macromolecules is lacking. Here we describe the discovery and characterisation of endo-acting enzymes from prominent mucin-degrading bacteria that target the polyLacNAc structures within oligosaccharide side chains of both animal and human mucins. These O-glycanases are part of the large and diverse glycoside hydrolase 16 (GH16) family and are often lipoproteins, indicating that they are surface located and thus likely involved in the initial step in mucin breakdown. These data provide a significant advance in our knowledge of the mechanism of mucin breakdown by the normal microbiota. Furthermore, we also demonstrate the potential use of these enzymes as tools to explore changes in O-glycan structure in a number of intestinal disease states.

Purification and biochemical/biophysical characterization of two hexosaminidases from the fresh water mussel, Lamellidens corrianus.

Two thermostable isoforms of a hexosaminidase were purified to homogeneity from the soluble extract of fresh water mussel Lamellidens corrianus, employing a variety of chromatographic techniques. Hexosaminidase A (HexA) is a heterodimer with subunit masses of ~80 and 55 kDa. Hexosaminidase B (HexB) is a homodimer with a subunit mass of 55-60 kDa. Circular dichroism spectroscopic studies indicated that both HexA and HexB contain ß-sheet as the major secondary structural component with considerably lower content of α-helix. The temperature and pH optima of both the isoforms were found to be 60 °C and 4.0, respectively. The IC50 values for HexA with N-acetyl-d-galactosamine, N-acetyl-d-glucosamine, d-galactosamine, d-glucosamine, methyl α-d-mannopyranoside and d-mannose are 3.7, 72.8, 307, 216, 244 and 128 mM, respectively, whereas the corresponding IC50 values for HexB were estimated as 5.1, 61, 68, 190, 92 and 133 mM, respectively. Kinetic parameters KM and Vmax for HexA and B with p-nitrophenyl N-acetyl-ß-d-glucosaminide are 4 mM, 0.23 µmol·min-1·mL-1 and 2.86 mM, 0.29 µmol·min-1·mL-1, respectively, and with p-nitrophenyl N-acetyl-ß-d-galactosaminide are 4.5 mM, 0.054 µmol·min-1·mL-1 and 1.4 mM, 0.14 µmol·min-1·mL-1, respectively. GalNAc inhibited both isoforms in a non-competitive manner, whereas a mixed mode of inhibition was observed with GlcNAc with both forms.

An enzymatic pathway in the human gut microbiome that converts A to universal O type blood.

Access to efficient enzymes that can convert A and B type red blood cells to 'universal' donor O would greatly increase the supply of blood for transfusions. Here we report the functional metagenomic screening of the human gut microbiome for enzymes that can remove the cognate A and B type sugar antigens. Among the genes encoded in our library of 19,500 expressed fosmids bearing gut bacterial DNA, we identify an enzyme pair from the obligate anaerobe Flavonifractor plautii that work in concert to efficiently convert the A antigen to the H antigen of O type blood, via a galactosamine intermediate. The X-ray structure of the N-acetylgalactosamine deacetylase reveals the active site and mechanism of the founding member of an esterase family. The galactosaminidase expands activities within the CAZy family GH36. Their ability to completely convert A to O of the same rhesus type at very low enzyme concentrations in whole blood will simplify their incorporation into blood transfusion practice, broadening blood supply.

Lacto-N-tetraose synthesis by wild-type and glycosynthase variants of the ß-N-hexosaminidase from Bifidobacterium bifidum.

Lacto-N-biose 1,2-oxazoline was prepared chemo-enzymatically and shown to be a donor substrate for ß-1,3-glycosylation of lactose by the wild-type and glycosynthase variants (D320E, D320A, Y419F) of Bifidobacterium bifidum ß-N-hexosaminidase. Lacto-N-tetraose, a core structure of human milk oligosaccharides, was formed in 20-60% yield of donor substrate (up to 8 mM product titre), depending on the degree of selectivity control by the enzyme used.

Contrasting effects of nitrogen and phosphorus additions on soil nitrous oxide fluxes and enzyme activities in an alpine wetland of the Tibetan Plateau.

Alpine wetlands are important ecosystems, but an increased availability of soil nutrients may affect their soil nitrous oxide (N2O) fluxes and key enzyme activities. We undertook a 3-year experiment of observing nitrogen (N) and/or phosphorus (P) addition to alpine wetland soils of the Tibetan Plateau, China, with measurements made of soil extracellular enzyme activities and soil N2O fluxes. Our study showed that soil N2O flux was significantly increased by 72% and 102% following N and N+P additions, respectively. N addition significantly increased acid phosphatase (AP) and ß-1, 4-N-acetyl-glucosaminidase (NAG) activities by 32% and 26%, respectively. P addition alone exerted a neutral effect on soil AP activities, while increasing NAG activities. We inferred that microbes produce enzymes based on 'resource allocation theory', but that a series of constitutive enzymes or the treatment duration interfere with this response. Our findings suggest that N addition increases N- and P-cycling enzyme activities and soil N2O flux, whereas P addition exerts a neutral effect on P-cycling enzyme activities and N2O flux after 3 years of nutrient applications to an alpine wetland.

Direct comparison of chitinolytic properties and determination of combinatory effects of mouse chitotriosidase and acidic mammalian chitinase.

Chitotriosidase (Chit1) and acidic mammalian chitinase (AMCase) have been implicated in food processing and various pathophysiological conditions such as chronic inflammatory diseases. By combination of the colorimetric analysis and fluorophore-assisted carbohydrate electrophoresis (FACE) method, we directly compared the chitinolytic properties of mouse Chit1 and AMCase and determined their combinatory effects in artificial and natural chitin substrates processing. Chit1 and AMCase display different dynamics of chitinolytic properties through acidic to neutral conditions. At pH2.0, the activity of AMCase was higher than that of Chit1 and stronger or comparable with that of Serratia marcescens chitinase B, a well-characterized bacterium chitinase. Changes of degradation products using different substrates indicate that AMCase and Chit1 have diverse properties under various pH conditions. Exposure of the chitin substrates to both Chit1 and AMCase did not indicate any mutual interference of these enzymes and showed no synergistic effect, in contrast to observations regarding some bacterial chitinases. Our results suggest that Chit1 and AMCase have no synergistic effect under physiological conditions.

Structural Insights into the Molecular Evolution of the Archaeal Exo-ß-d-Glucosaminidase.

The archaeal exo-ß-d-glucosaminidase (GlmA), a thermostable enzyme belonging to the glycosidase hydrolase (GH) 35 family, hydrolyzes chitosan oligosaccharides into monomer glucosamines. GlmA is a novel enzyme in terms of its primary structure, as it is homologous to both GH35 and GH42 ß-galactosidases. The catalytic mechanism of GlmA is not known. Here, we summarize the recent reports on the crystallographic analysis of GlmA. GlmA is a homodimer, with each subunit comprising three distinct domains: a catalytic TIM-barrel domain, an α/ß domain, and a ß1 domain. Surprisingly, the structure of GlmA presents features common to GH35 and GH42 ß-galactosidases, with the domain organization resembling that of GH42 ß-galactosidases and the active-site architecture resembling that of GH35 ß-galactosidases. Additionally, the GlmA structure also provides critical information about its catalytic mechanism, in particular, on how the enzyme can recognize glucosamine. Finally, we postulate an evolutionary pathway based on the structure of an ancestor GlmA to extant GH35 and GH42 ß-galactosidases.

Novel Glycosylated Naphthalimide-Based Activatable Fluorescent Probe: A Tool for the Assessment of Hexosaminidase Activity and Intracellular Hexosaminidase Imaging.

The development of effective detection methods for hexosaminidase is of great importance for the rapid screening of potential inhibitors in vitro and for the early diagnosis of related diseases ex vivo. In this study, the activatable fluorescent probes that are based on naphthalimide decorated with ethylene glycol units were synthesized using N-acetyl-ß-d-glucosaminide as a hexosaminidase-responsive group. When exposed to this enzyme, the glucoside-linked naphthalimide moiety of 1c can be cleaved quickly with significant changes in both color (from colorless to yellow) and fluorescence (from blue to green). Probe 1c shows better water-solubility and fluorescence properties than common substrate 4-methylumbelliferyl N-acetyl-ß-d-glucosaminide. Furthermore, the response mechanism of 1c to hexosaminidase was evaluated using HPLC analysis and TD-DFT calculations. Molecular docking was performed to investigate the interaction mode. In addition, 1c has successfully achieved the straightforward rapid discovery of effective hexosaminidase inhibitors. Fluorescence imaging experiments indicate that 1c has good cell safety and can be employed as a useful tool for detecting intracellular hexosaminidase activity.

The broad-specificity chitinases: their origin, characterization, and potential application.

Chitinases are hydrolases that catalyze the cleavage of the ß-1,4-O-glycosidic linkages in chitin, a polysaccharide abundantly found in nature. Although numerous chitinolytic enzymes have been studied in detail, relatively little is known about chitinases capable of broad specificity. Broad-specificity chitinases are a sort of novel chitinases possessing two or three different catalytic activities among exochitinase, endochitinase, and N-acetylglucosaminidase. In the light of the difference of module composition and catalytic mechanism, the broad-specificity chitinases included two broad categories, broad-specificity chitinases with a single catalytic domain or multi-catalytic domains. This broad-specificity chitinases have great potential in chitin conversion. In this review, we summarize all reported cases of broad-specificity chitinases and provide an overview of the recent findings on their origin, characterization, catalytic mechanism, and potential application. Moreover, in-depth study into these chitinases could contribute to our understanding of other broad-specificity enzymes which may have some benefits on progress of biotechnology.

Enzymatic Production and Enzymatic-Mass Spectrometric Fingerprinting Analysis of Chitosan Polymers with Different Nonrandom Patterns of Acetylation.

Chitosans, a family of ß-(1,4)-linked, partially N-acetylated polyglucosamines, are considered to be among the most versatile and most promising functional biopolymers. Chemical analysis and bioactivity studies revealed that the functionalities of chitosans strongly depend on the polymers' degree of polymerization and fraction of acetylation. More recently, the pattern of acetylation ( PA) has been proposed as another important parameter to influence functionalities of chitosans. We therefore carried out studies on the acetylation pattern of chitosan polymers produced by three recombinant fungal chitin deacetylases (CDAs) originating from different species, namely, Podospora anserina, Puccinia graminis f. sp. tritici, and Pestalotiopsis sp. We analyzed the chitosans by 1H NMR, 13C NMR, and SEC-MALS and established new methods for PA analysis based on enzymatic mass spectrometric fingerprinting and in silico simulations. Our studies strongly indicate that the different CDAs indeed produce chitosans with different PA. Finally, Zimm plot analysis revealed that enzymatically treated polymers differ with respect to their second virial coefficient and radius of gyration indicating an influence of PA on polymer-solvent interactions.

Utility of amniotic fluid chitotriosidase in the prenatal diagnosis of lysosomal storage disorders.

OBJECTIVE: Plasma chitotriosidase is a documented biomarker for certain lysosomal storage disorders. However, its clinical utility for prenatal samples is not elucidated yet. METHODS: We have established Reference intervals for amniotic fluid chitotriosidase using control amniotic fluids (n = 47) and compared the activity with amniotic fluids affected by lysosomal storage disorders (n = 25). RESULTS: The reference interval established was 0-6.76 nmol/h/ml. The amniotic fluids affected with LSDs exhibited elevation of chitotriosidase. The area under the curve (AUC) of receiver operating characteristic curve for affected vs. healthy was 0.987 indicating 98.6% accuracy of chitotriosidase in identifying pregnancies affected with LSDs. Among the different LSDs, Gaucher (202.00 ±â€¯35.27 nmol/h/ml) and Niemann-pick A/B (60.33 ±â€¯21.59 nmol/h/ml) showed very high levels of chitotriosidase. CONCLUSION: Amniotic fluid chitotriosidase has the potential to serve as a diagnostic marker for lysosomal storage disorders, more specifically for Gaucher and Niemann-Pick A/B.

Structure of the GH9 glucosidase/glucosaminidase from Vibrio cholerae.

Glycoside hydrolase family 9 (GH9) of carbohydrate-processing enzymes primarily consists of inverting endoglucanases. A subgroup of GH9 enzymes are believed to act as exo-glucosidases or exo-glucosaminidases, with many being found in organisms of the family Vibrionaceae, where they are proposed to function within the chitin-catabolism pathway. Here, it is shown that the GH9 enzyme from the pathogen Vibrio cholerae (hereafter referred to as VC0615) is active on both chitosan-derived and ß-glucoside substrates. The structure of VC0615 at 3.17 Šresolution is reported from a crystal form with poor diffraction and lattice disorder. VC0615 was highly refractory to crystallization efforts, with crystals only appearing using a high protein concentration under conditions containing the precipitant poly-γ-glutamic acid (PGA). The structure is highly mobile within the crystal lattice, which is likely to reflect steric clashes between symmetry molecules which destabilize crystal packing. The overall tertiary structure of VC0615 is well resolved even at 3.17 Šresolution, which has allowed the structural basis for the exo-glucosidase/glucosaminidase activity of this enzyme to be investigated.

Cell-Wall Recycling of the Gram-Negative Bacteria and the Nexus to Antibiotic Resistance.

The importance of the cell wall to the viability of the bacterium is underscored by the breadth of antibiotic structures that act by blocking key enzymes that are tasked with cell-wall creation, preservation, and regulation. The interplay between cell-wall integrity, and the summoning forth of resistance mechanisms to deactivate cell-wall-targeting antibiotics, involves exquisite orchestration among cell-wall synthesis and remodeling and the detection of and response to the antibiotics through modulation of gene regulation by specific effectors. Given the profound importance of antibiotics to the practice of medicine, the assertion that understanding this interplay is among the most fundamentally important questions in bacterial physiology is credible. The enigmatic regulation of the expression of the AmpC ß-lactamase, a clinically significant and highly regulated resistance response of certain Gram-negative bacteria to the ß-lactam antibiotics, is the exemplar of this challenge. This review gives a current perspective to this compelling, and still not fully solved, 35-year enigma.

Improvement of catalytic, thermodynamics and antifungal activity of constitutive Trichoderma longibrachiatum KT693225 exochitinase by covalent coupling to oxidized polysaccharides.

Our study full filled in two main goals preparation of constitutive exochitinase with low cost, utilizing non-chitin containing agricultural wastes, and improving the thermodynamics of purified Trichoderma longibrachiatum KT693225 exochitinase by covalent coupling to sodium periodate activated agar. Central composite design (CCD) was used to improve the chemical modification of Trichoderma longibrachiatum KT693225 exochitinase. Optimum temperature for conjugated exochitinase 60 °C was higher than native form 40 °C. Covalent coupling to oxidized agar caused 4.32, 2.75 and 2.44-fold increase in half-life values at 50, 55 and 60 °C, respectively. Also, conjugated exochitinase showed higher D-values (decimal reduction time) 1790.49 compared to 733.08 min for native form at 60 °C. Moreover, conjugated form had lower deactivation constant rate (kd) 0.39 × 10-3 min-1at 60 °C than native form 1.7 × 10-3 min-1. Native exochitinase exhibited higher activation energy (Ea) 3.39 Kcal·mol-1 and lower energy for denaturation (Ed) 6.88 Kcal·mol-1 compared to 3.21 and 13.05 Kcal·mol-1, respectively for conjugated form. The values of thermodynamic parameters for inactivation of native and conjugated exochitinase indicated that conjugation significantly decreased entropy (ΔS°) and increased enthalpy (ΔH°) and free energy (ΔG°) of deactivation. Conjugated exochitinase exhibited higher antifungal effect against Alternaria alternata, Fusarium oxysporium and Aspergillus niger than native form.

Dual transcriptomics reveals co-evolutionary mechanisms of intestinal parasite infections in blue mussels Mytilus edulis.

On theoretical grounds, antagonistic co-evolution between hosts and their parasites should be a widespread phenomenon but only received little empirical support so far. Consequently, the underlying molecular mechanisms and evolutionary steps remain elusive, especially in nonmodel systems. Here, we utilized the natural history of invasive parasites to document the molecular underpinnings of co-evolutionary trajectories. We applied a dual-species transcriptomics approach to experimental cross-infections of blue mussel Mytilus edulis hosts and their invasive parasitic copepods Mytilicola intestinalis from two invasion fronts in the Wadden Sea. We identified differentially regulated genes from an experimental infection contrast for hosts (infected vs. control) and a sympatry contrast (sympatric vs. allopatric combinations) for both hosts and parasites. The damage incurred by Mytilicola infection and the following immune response of the host were mainly reflected in cell division processes, wound healing, apoptosis and the production of reactive oxygen species (ROS). Furthermore, the functional coupling of host and parasite sympatry contrasts revealed the concerted regulation of chitin digestion by a Chitotriosidase 1 homolog in hosts with several cuticle proteins in the parasite. Together with the coupled regulation of ROS producers and antagonists, these genes represent candidates that mediate the different evolutionary trajectories within the parasite's invasion. The host-parasite combination-specific coupling of these effector mechanisms suggests that underlying recognition mechanisms create specificity and local adaptation. In this way, our study demonstrates the use of invasive species' natural history to elucidate molecular mechanisms of host-parasite co-evolution in the wild.

Human Chitotriosidase Does Not Catabolize Hyaluronan.

Humans express an enzyme that degrades chitin, called chitotriosidase, despite the fact that we do not produce chitin. One possible explanation for this is that chitinase also degrades hyaluronan, a polysaccharide that is abundant in human tissues and shares structural attributes in common with chitinase. The objective of this study was to determine whether human chitotriosidase is capable of hydrolyzing hyaluronan. Hyaluronan of various sizes under a range of pH conditions displayed no degradation when incubated with various chitinases over a period of 5 days, while commercial hyaluronidase readily digested the hyaluronan. Under the same conditions, recombinant chitinase but not our negative control chitinase, was able to digest chitosan. We conclude that human chitinase does not digest hyaluronan. Because chitin is a prominent component of certain fungi and insects, it seems likely that human chitinase evolved for roles in host defense rather than serving to catabolize the endogenous polymer hyaluronan.

Human Chitotriosidase: Catalytic Domain or Carbohydrate Binding Module, Who's Leading HCHT's Biological Function.

Chitin is an important structural component of numerous fungal pathogens and parasitic nematodes. The human macrophage chitotriosidase (HCHT) is a chitinase that hydrolyses glycosidic bonds between the N-acetyl-D-glucosamine units of this biopolymer. HCHT belongs to the Glycoside Hydrolase (GH) superfamily and contains a well-characterized catalytic domain appended to a chitin-binding domain (ChBDCHIT1). Although its precise biological function remains unclear, HCHT has been described to be involved in innate immunity. In this study, the molecular basis for interaction with insoluble chitin as well as with soluble chito-oligosaccharides has been determined. The results suggest a new mechanism as a common binding mode for many Carbohydrate Binding Modules (CBMs). Furthermore, using a phylogenetic approach, we have analysed the modularity of HCHT and investigated the evolutionary paths of its catalytic and chitin binding domains. The phylogenetic analyses indicate that the ChBDCHIT1 domain dictates the biological function of HCHT and not its appended catalytic domain. This observation may also be a general feature of GHs. Altogether, our data have led us to postulate and discuss that HCHT acts as an immune catalyser.