Purification and characterization of chitosanase and Exo-beta-D-glucosaminidase from a Koji mold, Aspergillus oryzae IAM2660

Synthesis of novel 5-[3-(4-chlorophenyl)-substituted-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione derivatives as potential anti-diabetic and anticancer agents

In this work, we developed a series of novel 5-[3-(4-chlorophenyl)-substituted-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione derivatives 4(a-e) via a one-pot multicomponent reaction. The structures of the compounds were confirmed using analytical and spectroscopic techniques. Also, the synthesized compounds were screened for their anti-diabetic activity, cytotoxicity and in silico studies. The activity results suggested that the compound 4e exhibited least IC50 values of 0.055 ± 0.002 µM, 0.050 ± 0.002 µM and 0.009 ± 0.001 µM for α-amylase, α-glucosidase and cytotoxicity respectively. Further, in silico molecular docking results revealed that all the obtained compounds effectively interacted with exo-β-D-glucosaminidase and P38 MAP kinase proteins with good binding energies. In that, 4e compound established the least binding energy of -9.6 and -9.1 kcal/mol, respectively. Moreover, our synthesized compounds were subjected to ADME studies, which suggested that all the synthesized compounds obeyed all five rules with good bioavailability and were suitable as drug leads against anti-diabetic and anticancer treatment.

Cell Wall Anchoring of a Bacterial Chitosanase in Lactobacillus plantarum Using a Food-Grade Expression System and Two Versions of an LP TG Anchor

Lactic acid bacteria (LAB) have attracted increasing interest recently as cell factories for the production of proteins as well as a carrier of proteins that are of interest for food and therapeutic applications. In this present study, we exploit a lactobacillal food-grade expression system derived from the pSIP expression vectors using the alr (alanine racemase) gene as the selection marker for the expression and cell-surface display of a chitosanase in Lactobacillus plantarum using two truncated forms of a LP × TG anchor. CsnA, a chitosanase from Bacillus subtilis 168 (ATCC23857), was fused to two different truncated forms (short-S and long-L anchors) of an LP × TG anchor derived from Lp_1229, a key-protein for mannose-specific adhesion in L. plantarum WCFS1. The expression and cell-surface display efficiency driven by the food-grade alr-based system were compared with those obtained from the erm-based pSIP system in terms of enzyme activities and their localisation on L. plantarum cells. The localization of the protein on the bacterial cell surface was confirmed by flow cytometry and immunofluorescence microscopy. The highest enzymatic activity of CsnA-displaying cells was obtained from the strain carrying the alr-based expression plasmid with short cell wall anchor S. However, the attachment of chitosanase on L. plantarum cells via the long anchor L was shown to be more stable compared with the short anchor after several repeated reaction cycles. CsnA displayed on L. plantarum cells is catalytically active and can convert chitosan into chito-oligosaccharides, of which chitobiose and chitotriose are the main products.

Characterization and antifungal activity of chitosanase produced by Pedobacter sp. PR-M6

To investigate the temperature requirements of chitosanase activity, as well as the degradation patterns generated by enzyme-induced chitosan oligomer hydrolysis, Pedobacter sp. PR-M6 was inoculated onto 0.5% colloidal chitosan medium agar plates. Cell growth was higher at 30 °C than at 20 °C during the initial 2 days of incubation. The protein content rapidly increased on day 1 at both temperatures and then it slowly increased at 20 °C and slowly decreased at 30 °C during the following 5 days of incubation. In order to characterize the electrophoretic pattern, Pedobacter sp. PR-M6 was cultured in 1% powder chitosan medium at 20 °C and 30 °C for 5 days after incubation and analyzed by SDS-PAGE. Four bands were visible, corresponding to ct1 (25 kDa), ct2 (17 kDa), ct3 (15 kDa), and ct4 (14 kDa), at both 20 °C and 30 °C. The optimal conditions for the activity of chitosanase produced from Pedobacter sp. PR-M6 were 60 °C and 1.81 enzyme units/mg protein. Two major isozyme bands (ct3 and ct4) exhibited their strongest chitosanase activity at 50 °C in SDS-PAGE gel. The reaction products generated from (GlcN)₂-(GlcN)₅ substrates at 60 °C after a 1 h incubation were investigated by thin-layer chromatography. Low-molecular weight chitosan and oligochitosan (LCOC) and soluble chitosan showed antifungal activity against A. brassicicola, B. cinerea, F. solani, and R. solani. LCOC exhibited higher antifungal activity than soluble chitosan. Moreover, LCOC treatments (500 ppm and 1000 ppm) inhibited conidia germination in A. brassicicola.

Characterization of a novel exo-chitosanase, an exo-chitobiohydrolase, from Gongronella butleri

An exo-chitosanase was purified from the culture filtrate of Gongronella butleri NBRC105989 to homogeneity by ammonium sulfate precipitation, followed by column chromatography using CM-Sephadex C-50 and Sephadex G-100. The enzyme comprised a monomeric protein with a molecular weight of approximately 47,000 according to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme exhibited optimum activity at pH 4.0, and was stable between pH 5.0 and 11.0. It was most active at 45°C, but was stable at temperatures below 30°C. The enzyme hydrolyzed soluble chitosan and glucosamine (GlcN) oligomers larger than tetramers, but did not hydrolyze N-acetylglucosamine (GlcNAc) oligomers. To clarify the mode of action of the enzyme, we used thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) to investigate the products resulting from the enzyme-catalyzed hydrolysis of chitosan and N¹-acetylchitohexaose [(GlcN)₅-GlcNAc] with a GlcNAc residue at the reducing end. The results indicated that the enzyme is a novel exo-type chitosanase, exo-chitobiohydrolase, that releases (GlcN)₂ from the non-reducing ends of chitosan molecules. Analyses of the hydrolysis products of partially N-acetylated chitooligosaccharides revealed that the enzyme cleaves both GlcN-GlcNAc and GlcNAc-GlcN bonds in addition to GlcN-GlcN bonds in the substrate.

Proteinase and glycoside hydrolase production is enhanced in solid-state fermentation by manipulating the carbon and nitrogen fluxes in Aspergillus oryzae

Soy sauce materials of soybean meal and wheat bran were evaluated in solid-state (koji) fermentation (SSF) and submerged fermentation (SmF) by Aspergillus oryzae. Proteinase production in SSF (2331 ± 39 U g^-1) was about 4.9 times higher than that in SmF (477 ± 13 U g^-1), and glycoside hydrolase was approximately 2 times higher in SSF than that in SmF. In addition, protein expression of iTRAQ analysis deepens our understanding of the secreting mechanism. Abundant proteinases (dipeptidase, dipeptidyl aminopeptidase, puromycin-sensitive aminopeptidase, Xaa-pro aminopeptidase, neutral protease 2 and leucine aminopeptidase 2), along with the glycoside hydrolase (glycoamylase, glucosidase and β-xylanase) were secreted at the late stage of SSF, but tripeptidyl peptidase sed 2 was proposed as an indispensable protease in SmF or the early stage of SSF. Several metabolites associated with the carbon flux and amino acid biosynthesis were proved to be regulated by the proteinase and glycoside hydrolase production.

Diversity of family GH46 chitosanases in Kitasatospora setae KM-6054

The genome of Kitasatospora setae KM-6054, a soil actinomycete, has three genes encoding chitosanases belonging to GH46 family. The genes (csn1-3) were cloned in Streptomyces lividans and the corresponding enzymes were purified from the recombinant cultures. The csn2 clone yielded two proteins (Csn2BH and Csn2H) differing by the presence of a carbohydrate-binding domain. Sequence analysis showed that Csn1 and Csn2H were canonical GH46 chitosanases, while Csn3 resembled chitosanases from bacilli. The activity of the four chitosanases was tested in a variety of conditions and on diverse chitosan forms, including highly N-deacetylated chitosan or chitosan complexed with humic or polyphosphoric acid. Kinetic parameters were also determined. These tests unveiled the biochemical diversity among these chitosanases and the peculiarity of Csn3 compared with the other three enzymes. The observed biochemical diversity is discussed based on structural 3D models and sequence alignment. This is a first study of all the GH46 chitosanases produced by a single microbial strain.

Enzymatic production of glucosamine and chitooligosaccharides using newly isolated exo-β-D-glucosaminidase having transglycosylation activity

Exochitosanase secreting fungus (A. fumigatus IIT-004) was isolated from fish waste using 1 % (w/v) chitosan as sole carbon source after multistage screening. Chitosan-dependent exochitosanase enzyme production (6 IU ml⁻¹) in log phase of growth (chitosan utilization rate 0.11 g g⁻¹ cell h⁻¹) was observed for Aspergillus fumigatus in chitosan minimal salt medium and there was no enzyme production in glucose medium. Enzyme production was found to be extracellular and subjected to purification by a number of steps like acetone fractionation as well as column chromatography. 40 % yield and 26-fold of enzyme purification was achieved after all the steps. Purified enzyme was characterized for optimum temperature, pH, ionic strength and substrate specificity. The K_m and V_max for purified exochitosanase enzyme was calculated to be 8 mg ml⁻¹ and 5.2 × 10⁻⁶ mol mg⁻¹ min⁻¹. Enzyme was immobilized on polyacrylonitrile nanofibres membrane matrix by adsorption as well as amidination. Enzymatic production of glucosamine was achieved using various chitosan substrates by free/immobilized exochitosanase and compared. Isolated and purified exochitosanase also showed transglycosylation activity.

Extracellular overexpression of chitosanase from Bacillus sp. TS in Escherichia coli

The chitosanase gene from a Bacillus sp. strain isolated from soil in East China was cloned and expressed in Escherichia coli. The gene had 1224 nucleotides and encoded a mature protein of 407 amino acid residues. The optimum pH and temperature of the purified recombinant chitosanase were 5.0 and 60 °C, respectively, and the enzyme was stable below 40 °C. The K m, V max, and specific activity of the enzyme were 1.19 mg mL(-1), 674.71 μmol min(-1) at 50 °C, and 555.3 U mg(-1), respectively. Mn(2+) was an activator of the recombinant chitosanase, while Co(2+) was an inhibitor. Hg(2+) and Cu(2+) inhibited the enzyme at 1 mM. The highest level of enzyme activity (186 U mL(-1)) was achieved in culture medium using high cell-density cultivation in a 7-L fermenter. The main products of chitosan hydrolyzed by recombinant chitosanase were (GlcN)3-6. The chitosanases was successfully secreted to the culture media through the widely used SecB-dependent type II pathway in E. coli. The high yield of the extracellular overexpression, relevant thermostability, and effective hydrolysis of commercial grade chitosan showed that this recombinant enzyme had a great potential for industrial applications.

Squid pen chitin chitooligomers as food colorants absorbers

One of the most promising applications of chitosanase is the conversion of chitinous biowaste into bioactive chitooligomers (COS). TKU033 chitosanase was induced from squid pen powder (SPP)-containing Bacillus cereus TKU033 medium and purified by ammonium sulfate precipitation and column chromatography. The enzyme was relatively more thermostable in the presence of the substrate and had an activity of 93% at 50 °C in a pH 5 buffer solution for 60 min. Furthermore, the enzyme used for the COS preparation was also studied. The enzyme products revealed various mixtures of COS that with different degrees of polymerization (DP), ranging from three to nine. In the culture medium, the fermented SPP was recovered, and it displayed a better adsorption rate (up to 96%) for the disperse dyes than the water-soluble food colorants, Allura Red AC (R40) and Tartrazne (Y4). Fourier transform-infrared spectroscopic (FT-IR) analysis proved that the adsorption of the dyes onto fermented SPP was a physical adsorption. Results also showed that fermented SPP was a favorable adsorber and could be employed as low-cost alternative for dye removal in wastewater treatment.

Bioproduction of chitooligosaccharides: present and perspectives

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

Production and purification of a fungal chitosanase and chitooligomers from Penicillium janthinellum D4 and discovery of the enzyme activators

Chitosanases have received much attention because of their wide range of applications. Although most fungal chitosanases use sugar as their major carbon source, in the present work, a chitosanase was induced from a squid pen powder (SPP)-containing Penicillium janthinellum D4 medium and purified by ammonium sulphate precipitation and combined column chromatography. The purified D4 chitosanase exhibited optimum activity at pH 7-9, 60°C and was stable at pH 7-11, 25-50°C. The D4 chitosanase that was used for chitooligomers preparation was studied. The enzyme products revealed various chitooligomers with different degrees of polymerisation (DP) from 3 to 9, as determined by a MALDI-TOF mass spectrometer, confirming the endo-type nature of the D4 chitosanase. D4 chitosanase activity was significantly inhibited by Cu(2+), Mn(2+), and EDTA. However, Fe(2+) activated or inhibited D4 chitosanases at different concentrations. The D4 chitosanase was also activated by some small synthetic boron-containing molecules with boronate ester side chains.

Classification of chitosanases by hydrolytic specificity toward N¹,N⁴-diacetylchitohexaose

The hydrolytic specificities of chitosanases were determined using N¹,N⁴-diacetylchitohexaose [(GlcN)₂-GlcNAc-(GlcN)₂-GlcNAc]. The results for the hydrolytic specificities of chitosanases belonging to subclasses I, II, and III toward chitohexaose and N¹,N⁴-diacetylchitohexaose agreed with previous results obtained by analysis of the hydrolysis products of partially N-acetylated chitosan. N¹,N⁴-Diacetylchitohexaose is a useful substrate to determine the hydrolytic specificity of chitosanase. On the other hand, chitosanases from Amycolatopsis sp. CsO-2 and Pseudomonas sp. A-01 showed broad cleavage specificity. They cleaved both the GlcNAc-GlcN and the GlcN-GlcNAc bonds in addition to the GlcN-GlcN bond in the substrate. Thus, both enzymes were new chitosanases. The chitosanases were divided into four subclasses according to their specificity for hydrolysis of the β-glycosidic linkages in partially N-acetylated chitosan.

Cloning and characterization of a gene coding for a major extracellular chitosanase from the koji mold Aspergillus oryzae

A gene coding for a major extracellular chitosanase was isolated from Aspergillus oryzae IAM2660. It had a multi-domain structure composed of a signal peptide, a catalytic domain, Thr- and Pro-rich linkers, and repeated peptides (the R3 domain) from the N-terminus. The R3 domain bound to insoluble powder chitosan, but it did not promote the hydrolysis rate of the chitosanase to any extent.

Modification of genetic regulation of a heterologous chitosanase gene in Streptomyces lividans TK24 leads to chitosanase production in the absence of chitosan

BACKGROUND

Chitosanases are enzymes hydrolysing chitosan, a β-1,4 linked D-glucosamine bio-polymer. Chitosan oligosaccharides have numerous emerging applications and chitosanases can be used for industrial enzymatic hydrolysis of chitosan. These extracellular enzymes, produced by many organisms including fungi and bacteria, are well studied at the biochemical and enzymatic level but very few works were dedicated to the regulation of their gene expression. This is the first study on the genetic regulation of a heterologous chitosanase gene (csnN106) in Streptomyces lividans.

RESULTS

Two S. lividans strains were used for induction experiments: the wild type strain and its mutant (ΔcsnR), harbouring an in-frame deletion of the csnR gene, encoding a negative transcriptional regulator. Comparison of chitosanase levels in various media indicated that CsnR regulates negatively the expression of the heterologous chitosanase gene csnN106. Using the ΔcsnR host and a mutated csnN106 gene with a modified transcription operator, substantial levels of chitosanase could be produced in the absence of chitosan, using inexpensive medium components. Furthermore, chitosanase production was of higher quality as lower levels of extracellular protease and protein contaminants were observed.

CONCLUSIONS

This new chitosanase production system is of interest for biotechnology as only common media components are used and enzyme of high degree of purity is obtained directly in the culture supernatant.

Characterization of the novel antifungal chitosanase PgChP and the encoding gene from Penicillium chrysogenum

The protein PgChP is a new chitosanase produced by Penicillium chrysogenum AS51D that showed antifungal activity against toxigenic molds. Two isoforms were found by SDS-PAGE in the purified extract of PgChP. After enzymatic deglycosylation, only the smaller isoform was observed by SDS-PAGE. Identical amino acid sequences were obtained from the two isoforms. Analysis of the molecular mass by electrospray ionization-mass spectrometry revealed six major peaks from 30 to 31 kDa that are related to different levels of glycosylation. The pgchp gene has 1,146 bp including four introns and an open reading frame encoding a protein of 304 amino acids. The translated open reading frame has a predicted mass of 32 kDa, with the first 21 amino acids comprising a signal peptide. Two N glycosylation consensus sequences are present in the protein sequence. The deduced sequence showed high identity with fungal chitosanases. A high level of catalytic activity on chitosan was observed. PgChP is the first chitosanase described from P. chrysogenum. Given that enzymes produced by this mold species are granted generally recognized as safe status, PgChP could be used as a food preservative against toxigenic molds and to obtain chitosan oligomers for food additives and nutraceuticals.

Chitosan modification and pharmaceutical/biomedical applications

Chitosan has received much attention as a functional biopolymer for diverse applications, especially in pharmaceutics and medicine. Our recent efforts focused on the chemical and biological modification of chitosan in order to increase its solubility in aqueous solutions and absorbability in the in vivo system, thus for a better use of chitosan. This review summarizes chitosan modification and its pharmaceutical/biomedical applications based on our achievements as well as the domestic and overseas developments: (1) enzymatic preparation of low molecular weight chitosans/chitooligosaccharides with their hypocholesterolemic and immuno-modulating effects; (2) the effects of chitin, chitosan and their derivatives on blood hemostasis; and (3) synthesis of a non-toxic ion ligand--D-Glucosaminic acid from oxidation of D-Glucosamine for cancer and diabetes therapy.

Isolation, characterization and heterologous expression of a novel chitosanase from Janthinobacterium sp. strain 4239

BACKGROUND

Chitosanases (EC 3.2.1.132) hydrolyze the polysaccharide chitosan, which is composed of partially acetylated beta-(1,4)-linked glucosamine residues. In nature, chitosanases are produced by a number of Gram-positive and Gram-negative bacteria, as well as by fungi, probably with the primary role of degrading chitosan from fungal and yeast cell walls for carbon metabolism. Chitosanases may also be utilized in eukaryotic cell manipulation for intracellular delivery of molecules formulated with chitosan as well as for transformation of filamentous fungi by temporal modification of the cell wall structures.However, the chitosanases used so far in transformation and transfection experiments show optimal activity at high temperature, which is incompatible with most transfection and transformation protocols. Thus, there is a need for chitosanases, which display activity at lower temperatures.

RESULTS

This paper describes the isolation of a chitosanase-producing, cold-active bacterium affiliated to the genus Janthinobacterium. The 876 bp chitosanase gene from the Janthinobacterium strain was isolated and characterized. The chitosanase was related to the Glycosyl Hydrolase family 46 chitosanases with Streptomyces chitosanase as the closest related (64% amino acid sequence identity). The chitosanase was expressed recombinantly as a periplasmic enzyme in Escherichia coli in amounts about 500 fold greater than in the native Janthinobacterium strain. Determination of temperature and pH optimum showed that the native and the recombinant chitosanase have maximal activity at pH 5-7 and at 45 degrees C, but with 30-70% of the maximum activity at 10 degrees C and 30 degrees C, respectively.

CONCLUSIONS

A novel chitosanase enzyme and its corresponding gene was isolated from Janthinobacterium and produced recombinantly in E. coli as a periplasmic enzyme. The Janthinobacterium chitosanase displayed reasonable activity at 10 degrees C to 30 degrees C, temperatures that are preferred in transfection and transformation experiments.

Chitinases are essential for sexual development but not vegetative growth in Cryptococcus neoformans

Cryptococcus neoformans is an opportunistic pathogen that mainly infects immunocompromised individuals. The fungal cell wall of C. neoformans is an excellent target for antifungal therapies since it is an essential organelle that provides cell structure and integrity. Importantly, it is needed for localization or attachment of known virulence factors, including melanin, phospholipase, and the polysaccharide capsule. The polysaccharide fraction of the cryptococcal cell wall is a complex structure composed of chitin, chitosan, and glucans. Chitin is an indispensable component of many fungal cell walls that contributes significantly to cell wall strength and integrity. Fungal cell walls are very dynamic, constantly changing during cell division and morphogenesis. Hydrolytic enzymes, such as chitinases, have been implicated in the maintenance of cell wall plasticity and separation of the mother and daughter cells at the bud neck during vegetative growth in yeast. In C. neoformans we identified four predicted endochitinases, CHI2, CHI21, CHI22, and CHI4, and a predicted exochitinase, hexosaminidase, HEX1. Enzymatic analysis indicated that Chi2, Chi22, and Hex1 actively degraded chitinoligomeric substrates. Chi2 and Hex1 activity was associated mostly with the cellular fraction, and Chi22 activity was more prominent in the supernatant. The enzymatic activity of Hex1 increased when grown in media containing only N-acetylglucosamine as a carbon source, suggesting that its activity may be inducible by chitin degradation products. Using a quadruple endochitinase deletion strain, we determined that the endochitinases do not affect the growth or morphology of C. neoformans during asexual reproduction. However, mating assays indicated that Chi2, Chi21, and Chi4 are each involved in sexual reproduction. In summary, the endochitinases were found to be dispensable for routine vegetative growth but not sexual reproduction.

Expression, purification, and characterization of exo-beta-D-glucosaminidase of Aspergillus sp. CJ22-326 from Escherichia coli

An exo-beta-D-glucosaminidase gene was cloned from Aspergillus sp. CJ22-326 and expressed in Escherichia coli. The purified protein showed an exo-chitosanase activity in a viscosimetric assay and TLC analysis. This is the first report on cloning of a gene encoding an Aspergillus sp. exo-beta-D-glucosaminidase.

Expression, purification and characterization of endo-type chitosanase of Aspergillus sp. CJ22-326 from Escherichia coli

An endo-chitosanase gene was cloned from Aspergillus sp. CJ22-326 and expressed in Escherichia coli. The purified protein showed an endo-chitosanase activity during viscosimetric assay and TLC analysis. The enzyme had higher chitosanolytic activity than previously reported fungal chitosanases.

Exo-β-d-glucosaminidase from Amycolatopsis orientalis: catalytic residues, sugar recognition specificity, kinetics, and synergism

Catalytic residues and the mode of action of the exo-beta-D-glucosaminidase (GlcNase) from Amycolatopsis orientalis were investigated using the wild-type and mutated enzymes. Mutations were introduced into the putative catalytic residues resulting in five mutated enzymes (D469A, D469E, E541D, E541Q, and S468N/D469E) that were successfully produced. The four single mutants were devoid of enzymatic activity, indicating that Asp469 and Glu541 are essential for catalysis as predicted by sequence alignments of enzymes belonging to GH-2 family. When mono-N-acetylated chitotetraose [(GlcN)3-GlcNAc] was hydrolyzed by the enzyme, the nonreducing-end glucosamine unit was produced together with the transglycosylation products. The rate of hydrolysis of the disaccharide, 2-amino-2-deoxy-D-glucopyranosyl 2-acetamido-2-deoxy-D-glucopyranose (GlcN-GlcNAc), was slightly lower than that of (GlcN)2, suggesting that N-acetyl group of the sugar residue located at (+1) site partly interferes with the catalytic reaction. The time-course of the enzymatic hydrolysis of the completely deacetylated chitotetraose [(GlcN)4] was quantitatively determined by high-performance liquid chromatography (HPLC) and used for in silico modeling of the enzymatic hydrolysis. The modeling study provided the values of binding free energy changes of +7.0, -2.9, -1.8, -0.9, -1.0, and -0.5 kcal/mol corresponding, respectively, to subsites (-2), (-1), (+1), (+2), (+3), and (+4). When chitosan polysaccharide was hydrolyzed by a binary enzyme system consisting of A. orientalis GlcNase and Streptomyces sp. N174 endochitosanase, the highest synergy in the rate of product formation was observed at the molar ratio 2:1. Thus, GlcNase would be an efficient tool for industrial production of glucosamine monosaccharide.

Two exo-beta-D-glucosaminidases/exochitosanases from actinomycetes define a new subfamily within family 2 of glycoside hydrolases

A GlcNase (exo-beta-D-glucosaminidase) was purified from culture supernatant of Amycolatopsis orientalis subsp. orientalis grown in medium with chitosan. The enzyme hydrolysed the terminal GlcN (glucosamine) residues in oligomers of GlcN with transglycosylation observed at late reaction stages. 1H-NMR spectroscopy revealed that the enzyme is a retaining glycoside hydrolase. The GlcNase also behaved as an exochitosanase against high-molecular-mass chitosan with K(m) and kcat values of 0.16 mg/ml and 2832 min(-1). On the basis of partial amino acid sequences, PCR primers were designed and used to amplify a DNA fragment which then allowed the cloning of the GlcNase gene (csxA) associated with an open reading frame of 1032 residues. The GlcNase has been classified as a member of glycoside hydrolase family 2 (GH2). Sequence alignments identified a group of CsxA-related protein sequences forming a distinct GH2 subfamily. Most of them have been annotated in databases as putative beta-mannosidases. Among these, the SAV1223 protein from Streptomyces avermitilis has been purified following gene cloning and expression in a heterologous host and shown to be a GlcNase with no detectable beta-mannosidase activity. In CsxA and all relatives, a serine-aspartate doublet replaces an asparagine residue and a glutamate residue, which were strictly conserved in previously studied GH2 members with beta-galactosidase, beta-glucuronidase or beta-mannosidase activity and shown to be directly involved in various steps of the catalytic mechanism. Alignments of several other GH2 members allowed the identification of yet another putative subfamily, characterized by a novel, serine-glutamate doublet at these positions.

Cloning and heterologous expression of the exo-β-d-glucosaminidase-encoding gene (gls93) from a filamentous fungus, Trichoderma reesei PC-3-7

We have previously reported on purification and characterization of an exo-beta-D-glucosaminidase (Gls93) from culture filtrate of Trichoderma reesei PC-3-7 grown on N-acetyl-D-glucosamine (GlcNAc). The corresponding gene of Gls93 was cloned and characterized in this work. To our knowledge, this is the first report on cloning of the gene encoding fungal exo-beta-D-glucosaminidase. This gene has no introns and encodes a polypeptide of 892 amino acids (aa) containing a secretion signal of 28 amino acids. Comparison of the amino acid sequence to known proteins and phylogenetic analysis indicated that gls93 belongs to the glycoside hydrolase family (GHF) 2 and should be further classified into a new subgroup, exo-beta-D-glucosaminidase subgroup. The gls93 transcription was biphasic when T. reesei was grown on GlcNAc, suggesting that the expression of this gene may be regulated by a complex mechanism, in which multiple regulatory proteins are involved. Furthermore, gls93 could be expressed in Pichia pastoris (ca. 0.49-mg/ml culture). The recombinant Gls93 had the two molecular forms, ca. 105 and 100 kDa, whose difference is caused by N-glycosylation. Both of them had the same properties such as specific activity and substrate specificity and showed only the activity of exo-beta-D-glucosaminidase but not those of beta-galactosidase, beta-glucuronidase, and beta-mannosidase belonging to GHF2.

Analysis of essential carboxylic amino acid residues for catalytic activity of fungal chitosanases by site-directed mutagenesis

A comparison of amino acid sequences of fungal chitosanases, belonging to family 75 of glycosyl hydrolases, revealed three carboxylic amino acid residues completely conserved among all of the chitosanases. To study the role of these residues in catalysis, they were replaced with other residues by site-directed mutagenesis in the chitosanase gene of Fusarium solani. The mutated genes were expressed in the yeast Saccharomyces cerevisiae and the resulting recombinant chitosanases were used in kinetic analysis. Chitosanases with Asp-175-->Asn and Glu-188-->Gln mutations were essentially inactive, whereas those with Asp-175-->Glu and Glu-188-->Asp mutations retained 25-50% specific activity as compared with the wild-type enzyme. The mutation of Asp-212-->Asn did not decrease specific activity to a large extent. Circular dichroism analysis confirmed that the mutant chitosanases had similar secondary structures to that of the wild-type enzyme. These results indicate that Asp-175 and Glu-188 are essential residues for the catalytic activity of chitosanase. Time-dependent (1)H-NMR analysis for the hydrolysis of D-glucosamine hexamer revealed that a fungal chitosanase is an inverting enzyme producing only the alpha anomeric form of reaction products.

Exploration of glycosyl hydrolase family 75, a chitosanase from Aspergillus fumigatus

A powerful endo-chitosanase (CSN) previously described for a large scale preparation of chito-oligosaccharides (Cheng, C.-Y., and Li, Y.-K. (2000) Biotechnol. Appl. Biochem. 32, 197-203) was cloned from Aspergillus fumigatus and further identified as a member of glycosyl hydrolase family 75. We report here a study of gene expression, functional characterization, and mutation analysis of this enzyme. Gene cloning was accomplished by reverse transcription-PCR and inverse PCR. Within the 1382-bp Aspergillus gene (GenBank accession number AY190324), two introns (67 and 82 bp) and an open reading frame encoding a 238-residue protein containing a 17-residue signal peptide were characterized. The recombinant mature protein was overexpressed as an inclusion body in Escherichia coli, rescued by treatment with 5 m urea, and subsequently purified by cation exchange chromatography. A time course 1H NMR study on the enzymatic formation of chito-oligosaccharides confirmed that this A. fumigatus CSN is an inverting enzyme. Tandem mass spectrum analysis of the enzymatic hydrolysate revealed that the recombinant CSN can cleave linkages of GlcNAc-GlcN and GlcN-GlcN in its substrate, suggesting that it is a subclass I chitosanase. In addition, an extensive site-directed mutagenesis study on 10 conserved carboxylic amino acids of glycosyl hydrolase family 75 was performed. This showed that among these various mutants, D160N and E169Q lost nearly all activity. Further investigation using circular dichroism measurements of D160N, E169Q, wild-type CSN, and other active mutants showed similar spectra, indicating that the loss of enzymatic activity in D160N and E169Q was not because of changes in protein structure but was caused by loss of the catalytic essential residue. We conclude that Asp160 and Glu169 are the essential residues for the action of A. fumigatus endo-chitosanase.

New chitosan-degrading strains that produce chitosanases similar to ChoA of Mitsuaria chitosanitabida

The betaproteobacterium Mitsuaria chitosanitabida (formerly Matsuebacter chitosanotabidus) 3001 produces a chitosanase (ChoA) that is classified in glycosyl hydrolase family 80. While many chitosanase genes have been isolated from various bacteria to date, they show limited homology to the M. chitosanitabida 3001 chitosanase gene (choA). To investigate the phylogenetic distribution of chitosanases analogous to ChoA in nature, we identified 67 chitosan-degrading strains by screening and investigated their physiological and biological characteristics. We then searched for similarities to ChoA by Western blotting and Southern hybridization and selected 11 strains whose chitosanases showed the most similarity to ChoA. PCR amplification and sequencing of the chitosanase genes from these strains revealed high deduced amino acid sequence similarities to ChoA ranging from 77% to 99%. Analysis of the 16S rRNA gene sequences of the 11 selected strains indicated that they are widely distributed in the beta and gamma subclasses of Proteobacteria and the Flavobacterium group. These observations suggest that the ChoA-like chitosanases that belong to family 80 occur widely in a broad variety of bacteria.

Purification and characterization of exo-beta-D-glucosaminidase from Aspergillus fumigatus S-26

An extracellular 104 kDa exo-beta-d-glucosaminidase was purified and characterized from the culture supernatant of Aspergillus fumigatus S-26, which showed exceptionally strong chitosanolytic enzyme activity. The purified enzyme showed optimum pH of 3.0-6.0 and optimum temperature of 50-60 degrees C, and was stable between pH 2.0 and 10.0 and under 35 degrees C. The Km, Vmax, and kcat were determined to be 1.0 mg chitosan/ml, 7.8x10(-8) mol/s/mg protein, and 28.3 s-1, respectively. The exo-beta-D-glucosaminidase was severely inactivated by Cu2+ and Hg2+ at 10 mM. 2-Hydroxy-5-nitrobenzyl bromide, N-bromosuccinimide, and p-chloromercuribenzoic acid inhibited the enzyme. The enzyme did not degrade chitin, cellulose, and starch. The exo-beta-D-glucosaminidase did not reduce the viscosity of chitosan solutions at early stage of reaction, suggesting the exo-type of cleavage in polymeric chitosan chains. The exo-beta-D-glucosaminidase liberated only GlcN from chitosan, and GlcN plus the one-residue shortened oligomers from (GlcN)2-7. The exo-beta-D-glucosaminidase exhibited transglycosylation activity, resulting in the one-residue elongated oligomers.

Purification and characterization of chitosanase from Bacillus sp. strain KCTC 0377BP and its application for the production of chitosan oligosaccharides

For the enzymatic production of chitosan oligosaccharides from chitosan, a chitosanase-producing bacterium, Bacillus sp. strain KCTC 0377BP, was isolated from soil. The bacterium constitutively produced chitosanase in a culture medium without chitosan as an inducer. The production of chitosanase was increased from 1.2 U/ml in a minimal chitosan medium to 100 U/ml by optimizing the culture conditions. The chitosanase was purified from a culture supernatant by using CM-Toyopearl column chromatography and a Superose 12HR column for fast-performance liquid chromatography and was characterized according to its enzyme properties. The molecular mass of the enzyme was estimated to be 45 kDa by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme demonstrated bifunctional chitosanase-glucanase activities, although it showed very low glucanase activity, with less than 3% of the chitosanase activity. Activity of the enzyme increased with an increase of the degrees of deacetylation (DDA) of the chitosan substrate. However, the enzyme still retained 72% of its relative activity toward the 39% DDA of chitosan, compared with the activity of the 94% DDA of chitosan. The enzyme produced chitosan oligosaccharides from chitosan, ranging mainly from chitotriose to chitooctaose. By controlling the reaction time and by monitoring the reaction products with gel filtration high-performance liquid chromatography, chitosan oligosaccharides with a desired oligosaccharide content and composition were obtained. In addition, the enzyme was efficiently used for the production of low-molecular-weight chitosan and highly acetylated chitosan oligosaccharides. A gene (csn45) encoding chitosanase was cloned, sequenced, and compared with other functionally related genes. The deduced amino acid sequence of csn45 was dissimilar to those of the classical chitosanase belonging to glycoside hydrolase family 46 but was similar to glucanases classified with glycoside hydrolase family 8.

Characterization of an exo-beta-D-glucosaminidase involved in a novel chitinolytic pathway from the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1

We previously clarified that the chitinase from the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1 produces diacetylchitobiose (GlcNAc(2)) as an end product from chitin. Here we sought to identify enzymes in T. kodakaraensis that were involved in the further degradation of GlcNAc(2). Through a search of the T. kodakaraensis genome, one candidate gene identified as a putative beta-glycosyl hydrolase was found in the near vicinity of the chitinase gene. The primary structure of the candidate protein was homologous to the beta-galactosidases in family 35 of glycosyl hydrolases at the N-terminal region, whereas the central region was homologous to beta-galactosidases in family 42. The purified protein from recombinant Escherichia coli clearly showed an exo-beta-D-glucosaminidase (GlcNase) activity but not beta-galactosidase activity. This GlcNase (GlmA(Tk)), a homodimer of 90-kDa subunits, exhibited highest activity toward reduced chitobiose at pH 6.0 and 80 degrees C and specifically cleaved the nonreducing terminal glycosidic bond of chitooligosaccharides. The GlcNase activity was also detected in T. kodakaraensis cells, and the expression of GlmA(Tk) was induced by GlcNAc(2) and chitin, strongly suggesting that GlmA(Tk) is involved in chitin catabolism in T. kodakaraensis. These results suggest that T. kodakaraensis, unlike other organisms, possesses a novel chitinolytic pathway where GlcNAc(2) from chitin is first deacetylated and successively hydrolyzed to glucosamine. This is the first report that reveals the primary structure of GlcNase not only from an archaeon but also from any organism.

Cloning and characterization of a chitosanase gene from the koji mold Aspergillus oryzae strain IAM 2660

A genomic copy of the gene coding for chitosanase (csnA) was isolated from Aspergillus oryzae IAM 2660. A. oryzae csnA contains an open reading frame that encodes a polypeptide of 245 amino acids with a calculated molecular mass of 26,500 Da. The deduced amino acid sequence of A. oryzae csnA indicates extensive similarities to those of other fungal chitosanases.