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Structure of the gene encoding chitinase D of Bacillus circulans WL-12 and possible homology of the enzyme to other prokaryotic chitinases and class III plant chitinases.

The gene (chiD) encoding the precursor of chitinase D was found to be located immediately upstream of the chiA gene, encoding chitinase A1, which is a key enzyme in the chitinase system of Bacillus circulans WL-12. Sequencing analysis revealed that the deduced polypeptide encoded by the chiD gene was 488 amino acids long and the distance between the coding regions of the chiA and chiD genes was 103 bp. Remarkable similarity was observed between the N-terminal one-third of chitinase D and the C-terminal one-third of chitinase A1. The N-terminal 47-amino-acid segment (named ND) of chitinase D showed a 61.7% amino acid match with the C-terminal segment (CA) of chitinase A1. The following 95-amino-acid segment (R-D) of chitinase D showed 62.8 and 60.6% amino acid matches, respectively, to the previously reported type III-like repeating units R-1 and R-2 in chitinase A1, which were shown to be homologous to the fibronectin type III sequence. A 73-amino-acid segment (residues 247 to 319) located in the putative activity domain of chitinase D was found to show considerable sequence similarity not only to other bacterial chitinases and class III higher-plant chitinases but also to Streptomyces plicatus endo-beta-N-acetylglucosaminidase H and the Kluyveromyces lactis killer toxin alpha subunit. The evolutionary and functional meanings of these similarities are discussed.

Amino Acid Sequence↗

Chitinase inhibitor allosamidin is a signal molecule for chitinase production in its producing Streptomyces II. Mechanism for regulation of chitinase production by allosamidin through a two-component regulatory system.

In Streptomyces sp. AJ9463, a producer of chitinase inhibitor allosamidin, allosamidin strongly enhances production of the chitinase mainly secreted to the culture broth in a chitin medium. To clarify the mechanism for regulation of the chitinase production by allosamidin, a disruption experiment of genes encoding proteins constructing a two-component regulatory system present at 5'-upstream region of the chitinase gene was performed. In the disruptant obtained, allosamidin could not promote the chitinase production, but N, N'-diacetylchitobiose, which also enhances production of the same chitinase more weakly than allosamidin, promoted the chitinase production similarly to the case observed in the wild-type strain. Furthermore, by the experiment in an inorganic salt solution, it was shown that allosamidin could not induce the chitinase production without addition of N, N'-diacetylchitobiose. These results show that allosamidin can activate transcription of the chitinase gene through the two-component regulatory system in the presence of N, N'-diacetylchitobiose.

Acetylglucosamine↗

Chitinase inhibitor allosamidin is a signal molecule for chitinase production in its producing Streptomyces I. Analysis of the chitinase whose production is promoted by allosamidin and growth accelerating activity of allosamidin.

Allosamidin, a typical secondary metabolite of Streptomyces, has been known as a chitinase inhibitor. We found that allosamidin can dramatically promote chitinase production and growth of its producer, Streptomyces sp. AJ9463, in a chitin medium at a few hundred nM. Allosamidin promoted production of the main chitinase detected in the culture filtrate and the chitin-hydrolytic activity of the chitinase was not inhibited by allosamidin at the concentration. The gene encoding the chitinase showed that it is a family 18 chitinase and it was revealed that two genes encoding proteins constructing two-component regulatory system were present at 5'-upstream region of the chitinase gene. Allosamidin is located in the microbial mycelia cultured in a medium without chitin, but it was released from the mycelia by responding to chitin. These results show that allosamidin acts as a key signal molecule for chitinase production in its producing strain, which may be useful for its growth in chitin-rich environment.

Acetylglucosamine↗

Comparison of chitinase isozymes from yam tuber--enzymatic factor controlling the lytic activity of chitinases.

To evaluate the anti-pathogen activity of chitinases, we developed a new method for measuring the lytic activity, and investigated the correlation of the lytic activity with the enzymatic properties by using four chitinase isozymes, Chitinases E, F, H1 and G, which had been purified from yam tubers by column chromatography. Chitinases E, F and H1 had high lytic activity against the plant pathogen, Fusarium oxysporum, but Chitinase G did not. Chitinase E, which is the family 19 chitinase, was similar to Chitinases F and G in its antigenecity, but not to Chitinase H1 or H2. Chitinases H1 and H2 were recognized by the anti-Bombyx mori chitinase antibody, suggesting that Chitinases H1 and H2 are family 18 chitinases like B. mori chitinases. Chitinases E, F and H1 had two optimum pH ranges of 3-4 and 7.5-9 toward glycolchitin, but Chitinase G had only one optimum pH value of 5. Chitinases E, F and H1 had higher affinity to the polymer substrate, glycolchitin, than Chitinase G. These results suggest that the lytic activity of plant chitinases may be related to the chitin affinity and probably to the characteristic optimum pH value, or two values, but not related to its classification. The correlation of the lytic activity of a chitinase isozyme with its elicitor specificity is also discussed.

Animals↗

Chitinase system of Bacillus circulans WL-12 and importance of chitinase A1 in chitin degradation.

Bacillus circulans WL-12, isolated as a yeast cell wall-lytic bacterium, secretes a variety of polysaccharide-degrading enzymes into culture medium. When chitinases of the bacterium were induced with chitin, six distinct chitinase molecules were detected in the culture supernatant. These chitinases (A1, A2, B1, B2, C, and D) showed the following distinct sizes and isoelectric points: Mr 74,000, pI 4.7 (A1); Mr 69,000, pI 4.5 (A2); Mr 38,000, pI 6.6 (B1); Mr 38,000, pI 5.9 (B2); Mr 39,000, pI 8.5 (C); and Mr 52,000, pI 5.2 (D). Among these chitinases, A1 and A2 had the highest colloidal-chitin-hydrolyzing activities. Chitinase A1 showed a strong affinity to insoluble substrate chitin. Purified chitinase A1 released predominantly chitobiose [(GlcNAc)2] and a trace amount of N-acetylglucosamine (GlcNAc) from colloidal chitin. N-terminal amino acid sequence analysis of chitinases A1 and A2 indicated that chitinase A2 was generated from chitinase A1, presumably by proteolytic removal of a C-terminal portion of chitinase A1. Since chitinase A2 did not have the ability to bind to chitin, the importance of the C-terminal region of chitinase A1 to the strong affinity of chitinase A1 to substrate chitin was suggested. Strong affinity of the chitinase seemed to be required for complete degradation of insoluble substrate chitin. From these results, it was concluded that chitinase A1 is the key enzyme in the chitinase system of this bacterium.

Amino Acid Sequence↗

A complete survey of Trichoderma chitinases reveals three distinct subgroups of family 18 chitinases.

Genome-wide analysis of chitinase genes in the Hypocrea jecorina (anamorph: Trichoderma reesei) genome database revealed the presence of 18 ORFs encoding putative chitinases, all of them belonging to glycoside hydrolase family 18. Eleven of these encode yet undescribed chitinases. A systematic nomenclature for the H. jecorina chitinases is proposed, which designates the chitinases corresponding to their glycoside hydrolase family and numbers the isoenzymes according to their pI from Chi18-1 to Chi18-18. Phylogenetic analysis of H. jecorina chitinases, and those from other filamentous fungi, including hypothetical proteins of annotated fungal genome databases, showed that the fungal chitinases can be divided into three groups: groups A and B (corresponding to class V and III chitinases, respectively) also contained the so Trichoderma chitinases identified to date, whereas a novel group C comprises high molecular weight chitinases that have a domain structure similar to Kluyveromyces lactis killer toxins. Five chitinase genes, representing members of groups A-C, were cloned from the mycoparasitic species H. atroviridis (anamorph: T. atroviride). Transcription of chi18-10 (belonging to group C) and chi18-13 (belonging to a novel clade in group B) was triggered upon growth on Rhizoctonia solani cell walls, and during plate confrontation tests with the plant pathogen R. solani. Therefore, group C and the novel clade in group B may contain chitinases of potential relevance for the biocontrol properties of Trichoderma.

3' Untranslated Regions↗

The third chitinase gene (chiC) of Serratia marcescens 2170 and the relationship of its product to other bacterial chitinases.

The third chitinase gene (chiC) of Serratia marcescens 2170, specifying chitinases C1 and C2, was identified. Chitinase C1 lacks a signal sequence and consists of a catalytic domain belonging to glycoside hydrolase family 18, a fibronectin type III-like domain (Fn3 domain) and a C-terminal chitin-binding domain (ChBD). Chitinase C2 corresponds to the catalytic domain of C1 and is probably generated by proteolytic removal of the Fn3 and ChBDs. The loss of the C-terminal portion reduced the hydrolytic activity towards powdered chitin and regenerated chitin, but not towards colloidal chitin and glycol chitin, illustrating the importance of the ChBD for the efficient hydrolysis of crystalline chitin. Phylogenetic analysis showed that bacterial family 18 chitinases can be clustered in three subfamilies which have diverged at an early stage of bacterial chitinase evolution. Ser. marcescens chitinase C1 is found in one subfamily, whereas chitinases A and B of the same bacterium belong to another subfamily. Chitinase C1 is the only Ser. marcescens chitinase that has an Fn3 domain. The presence of multiple, divergent, chitinases in a single chitinolytic bacterium is perhaps necessary for efficient synergistic degradation of chitin.

Amino Acid Sequence↗

Identification of glutamic acid 204 and aspartic acid 200 in chitinase A1 of Bacillus circulans WL-12 as essential residues for chitinase activity.

Prokaryotic chitinases, class III plant chitinases, yeast chitinases, and endo-beta-N-acetylglucosaminidases share weak amino acid sequence similarities at the certain region of each enzyme. These regions have been assumed to be important for catalytic activities of the enzymes. To verify this assumption, three amino acid residues (Ser-160, Asp-200, Glu-204) in chitinase A1 of Bacillus circulans WL-12 were chosen, based on the amino acid sequence alignment of the regions sharing sequence similarity, and were replaced by site-directed mutagenesis. Kinetic parameters for 4-methylumbelliferyl-N,N',N"-triacetylchitotriose hydrolysis were determined with wild-type and seven mutant chitinases. Chitinases with Glu-204-->Gln mutation and Glu-204-->Asp mutation were essentially inactive and kcat values of these chitinases were approximately 1/5,000 and 1/17,000 of that of wild-type chitinase, respectively. Asp-200-->Asn mutation decreased the kcat value to approximately 1/350 of that of the wild-type enzyme, while the Km value decreased only slightly. On the other hand, neither the kcat value nor the Km value was affected by Asp-200-->Glu mutation. Thus, it appeared that Glu-204 and Asp-200 are directly involved in the catalytic events of chitinase A1. The role of the carboxyl group of Asp-200 can be fully substituted by that of Glu residue. The Ser-160-->Ala mutant retained 10% activity of the wild-type chitinase indicating that the hydroxyl group of Ser-160 is not absolutely required for the catalytic activity. These results indicate a lysozyme-type catalytic mechanism of the chitinase.

Amino Acid Sequence↗

Sinorhizobium meliloti-induced chitinase gene expression in Medicago truncatula ecotype R108-1: a comparison between symbiosis-specific class V and defence-related class IV chitinases.

The Medicago truncatula (Gaertn.) ecotypes Jemalong A17 and R108-1 differ in Sinorhizobium meliloti-induced chitinase gene expression. The pathogen-inducible class IV chitinase gene, Mtchit 4, was strongly induced during nodule formation of the ecotype Jemalong A17 with the S. meliloti wild-type strain 1021. In the ecotype R108-1, the S. meliloti wild types Sm1021 and Sm41 did not induce Mtchit 4 expression. On the other hand, expression of the putative class V chitinase gene, Mtchit 5, was found in roots of M. truncatula cv. R108-1 nodulated with either of the rhizobial strains. Mtchit 5 expression was specific for interactions with rhizobia. It was not induced in response to fungal pathogen attack, and not induced in roots colonized with arbuscular mycorrhizal (AM) fungi. Elevated Mtchit 5 gene expression was first detectable in roots forming nodule primordia. In contrast to Mtchit 4, expression of Mtchit 5 was stimulated by purified Nod factors. Conversely, Mtchit 4 expression was strongly elevated in nodules formed with the K-antigen-deficient mutant PP699. Expression levels of Mtchit 5 were similarly increased in nodules formed with PP699 and its parental wild-type strain Sm41. Phylogenetic analysis of the deduced amino acid sequences of Mtchit 5 (calculated molecular weight = 41,810 Da, isoelectric point pH 7.7) and Mtchit 4 (calculated molecular weight 30,527 Da, isoelectric point pH 4.9) revealed that the putative Mtchit 5 chitinase forms a separate clade within class V chitinases of plants, whereas the Mtchit 4 chitinase clusters with pathogen-induced class IV chitinases from other plants. These findings demonstrate that: (i) Rhizobium-induced chitinase gene expression in M. truncatula occurs in a plant ecotype-specific manner, (ii) Mtchit 5 is a putative chitinase gene that is specifically induced by rhizobia, and (iii) rhizobia-specific and defence-related chitinase genes are differentially influenced by rhizobial Nod factors and K antigens.

Amino Acid Sequence↗

A new class of tobacco chitinases homologous to bacterial exo-chitinases displays antifungal activity.

A novel chitinase gene of tobacco was isolated and characterized by DNA sequence analysis of a genomic clone and a cDNA clone. Comparative sequence analysis of both clones showed an identity of 94%. The proteins encoded by these sequences do not correspond to any of the previously characterized plant chitinases of classes I-IV and are designated as class V chitinases. Comparison of the chitinase class V peptide sequence with sequences in the Swiss Protein databank revealed significant sequence similarity with bacterial exo-chitinases from Bacillus circulans, Serratia marcescens and Streptomyces plicatus. It was demonstrated that class V chitinase gene expression is induced after treatment of tobacco with different forms of stress, like TMV-infection, ethylene treatment, wounding or ultraviolet irradiation. Two related chitinase class V proteins of 41 and 43 kDa were purified from Samsun NN tobacco leaves inoculated with tobacco mosaic virus. The proteins were purified by Chelating Superose chromatography and gel filtration. In vitro assays demonstrated that class V chitinases have endo-chitinase activity and exhibit antifungal activity toward Trichoderma viride and Alternaria radicina. In addition, it was shown that class V chitinase acts synergistically with tobacco class I beta-1,3-glucanase against Fusarium solani germlings.

Amino Acid Sequence↗

Cloning, expression and functional characterisation of chitinase from larvae of tomato moth (Lacanobia oleracea): a demonstration of the insecticidal activity of insect chitinase.

Chitinases are vital to moulting in insects, and may also affect gut physiology through their involvement in peritrophic membrane turnover. A cDNA encoding chitinase was cloned from larvae of tomato moth (Lacanobia oleracea), a Lepidopteran pest of crops. The predicted protein contains 553 amino acid residues, with a signal peptide of 20 a.a. Sequence comparison showed 75-80% identity with other Lepidopteran chitinases. L. oleracea chitinase was produced as a functional recombinant enzyme in the yeast Pichia pastoris. A fusion protein containing chitinase joined to the N-terminus of snowdrop lectin (GNA) was also produced, to determine whether GNA could deliver chitinase to the haemolymph of Lepidopteran larvae after oral ingestion. The purified recombinant proteins exhibited similar levels of chitinase activity in vitro. Both proteins were highly toxic to L. oleracea larvae on injection, causing 100% mortality at low dose (2.5 microg/g insect). Injection of chitinase prior to the moult resulted in decreased cuticle thickness. The recombinant proteins caused chronic effects when fed, causing reductions in larval growth and food consumption by up to 60%. The oral toxicity of chitinase was not increased by attaching GNA in the fusion protein, due to degradation in the larval gut, preventing GNA acting as a "carrier".

Amino Acid Sequence↗

Gene cloning of chitinase A1 from Bacillus circulans WL-12 revealed its evolutionary relationship to Serratia chitinase and to the type III homology units of fibronectin.

A chitinase gene of Bacillus circulans WL-12 was cloned into Escherichia coli by transforming HB101 cells with a recombinant plasmid composed of chromosomal DNA fragments prepared from B. circulans WL-12 and the plasmid vector pKK223-3. DNA sequencing analysis revealed that the region necessary for the normal expression of chitinase activity contained one open reading frame of 2097 base pairs which codes for the precursor of chitinase A1. The precursor of chitinase A1 contained a long signal sequence of 41 amino acids with an extremely long N-terminal hydrophilic segment of 15 amino acids. Cloned chitinase produced in E. coli had at its N terminus an additional 8 amino acids that were not found in B. circulans mature chitinase A1. The N-terminal two-thirds of the deduced amino acid sequence of chitinase A1 showed a 33% amino acid match to chitinase A of Serratia marcescens. This region of chitinase A1 is immediately followed by tandemly repeating 95-amino acid segments that are 70% homologous to each other. Statistical analysis revealed that these repeating segments are homologous to the type III homology units of fibronectin, a multifunctional extracellular matrix and plasma protein of higher eukaryotes. This observation indicates that type III homology units originated prior to the emergence of eukaryotes and may be distributed in a wide range of organisms.

Amino Acid Sequence↗

Examination of the role of tyrosine-174 in the catalytic mechanism of the Arabidopsis thaliana chitinase: comparison of variant chitinases generated by site-directed mutagenesis and expressed in insect cells using baculovirus vectors.

Using the catalytic mechanism of lysozyme as a paradigm for the mechanism of other enzymes that catalyze the hydrolysis of beta-1,4-glycosidic linkages, including chitinase, we have examined the effect of chemical modification with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) on the reaction catalyzed by Zea mays chitinase. Inactivation with EDC did not result in derivatization of essential carboxylic acid residues, but resulted in the selective modification of a single essential tyrosine residue (Verburg, J. G., Smith, C. E., Lisek, C. A., and Huynh, Q. K., 1991, J. Biol. Chem. 267, 3886-3893). Here, we examine the role of the homologous tyrosine residue in the catalytic mechanism of the Arabidopsis thaliana chitinase. Tyrosine-174 of the Arabidopsis chitinase was replaced, with phenylalanine, alanine, histidine, and methionine by site-directed mutagenesis, and the variant chitinases were expressed in insect cells using baculovirus transfer vectors. A comparison of the reaction catalyzed by each of the variant enzymes indicates that substitution of another amino acid for Tyr-174 alters, but does not eliminate, enzymatic activity. Estimates of the specific activities of the variant chitinases reveal that substitution of His for Tyr-174 has a minimal effect on catalysis, the specific activities of the Phe and Met variants are approximately equivalent to each other, but are 60% the specific activity of wild-type Arabidopsis chitinase, and the specific activity of the Ala variant is only 40% that of wild-type. The observation that the Arabidopsis chitinase is tolerant to mutagenesis at this position suggests that Tyr-174 does not participate directly in catalysis.

Amino Acid Sequence↗

A tobacco gene encoding a novel basic class II chitinase: a putative ancestor of basic class I and acidic class II chitinase genes.

Various chitinases have been identified in plants and categorized into several groups based on the analysis of their sequences and domains. We have isolated a tobacco gene that encodes a predicted polypeptide consisting of a 20-amino acid N-terminal signal peptide, followed by a 245-amino acid chitinolytic domain. Although the predicted mature protein is basic and shows greater sequence identity to basic class I chitinases (75%) than to acidic class II chitinases (67%), it lacks the N-terminal cysteine-rich domain and the C-terminal vacuolar targeting signal that is diagnostic for class I chitinases. Therefore, this gene appears to encode a novel, basic, class II chitinase, which we have designated NtChia2;B1. Accumulation of Chia2;B1 mRNA was induced in leaves in association with the local-lesion response to tobacco mosaic virus (TMV) infection, and in response to treatment with salicylic acid, but was only slightly induced by treatment with ethephon. Little or no Chia2;B1 mRNA was detected in roots, flowers, and cell-suspension cultures, in which class I chitinase mRNAs accumulate to high concentrations. Sequence comparisons of Chia2;B1 with known tobacco class I and class II chitinase genes suggest that Chia2;B1 might encode an ancestral prototype of the present-day class I and class II isoforms. Possible mechanisms for chitinase gene evolution are discussed.

Amino Acid Sequence↗

The complete amino acid sequence of yam (Dioscorea japonica) chitinase. A newly identified acidic class I chitinase.

The complete amino acid sequence of acidic chitinase from yam (Dioscorea japonica) aerial tubers was determined. The protein is composed of a single polypeptide chain of 250 amino acid residues and has a calculated molecular mass of 27,890 Da. There is an NH2-terminal domain, a hinge region, and a main structure, typical for class I chitinases (Shinshi, H., Neuhaus, J.-M., Ryals, J., and Meins, F., Jr. (1990) Plant Mol. Biol. 14, 357-368). We have obtained the first evidence for an acidic class I chitinase. Comparison with sequences of other class I chitinases revealed approximately 40% sequence similarity, a value lower than that for other class I chitinases (70-80%). We assume that there is a local conformational change in the molecule; cysteine residues that probably form disulfide bonds are completely conserved, with the exception of Cys-178. The difference in structure between this chitinase and other basic class I chitinases suggests that acidic and basic isoforms should be grouped into subclasses; this protein is an ethylene- or a pathogen-independent chitinase produced by a gene that is inherent in the tuber.

Amino Acid Sequence↗

Characterization of monoclonal antibodies to chitinase A1 and enhancement of chitinase A1 activity by monoclonal antibodies.

A total of eleven hybridomas which secrete antibodies against chitinase A1 were established. Among the eleven monoclonal antibodies (MAbs) obtained, six recognized the catalytic domain, three recognized the type III region and two recognized the chitin binding domain of chitinase A1. Of the two MAbs which recognized the chitin binding domain one was found to also react with chitinase D, but none of the other MAbs which recognized either the type III region or the chitin binding domain reacted with chitinase D despite the extensive amino acid sequence similarity between both the type III and chitin binding domains of the two chitinases. Two of the eleven MAbs enhanced chitinase activity significantly, while the other MAbs did not have any significant effect on chitinase A1 activity.

Animals↗

Transmission-blocking activity of a chitinase inhibitor and activation of malarial parasite chitinase by mosquito protease.

During development in the mosquito midgut, malarial parasites must traverse a chitin-containing peritrophic matrix (PM) that forms around the food bolus. Previously Huber et al. [Huber, M., Cabib, E. & Miller, L. H. (1991) Proc. Natl. Acad. Sci. USA 88, 2807-2810] reported that the parasite secretes a protein with chitinase activity, and they suggested that parasite chitinase (EC 3.2.1.14) plays an important role in the parasite's egress from the blood meal. We found that allosamidin, a specific inhibitor of chitinase, completely blocked oocyst development in vivo and thus blocked malaria parasite transmission. Addition of exogenous chitinase to the blood meal prevented the PM from forming and reversed the transmission-blocking activity of allosamidin. Using exogenous chitinase, we also found that the PM does not limit the number of parasites that develop into oocysts, suggesting that the parasite produces sufficient quantities of chitinase to penetrate this potential barrier. In addition, we found that treatment of parasite chitinase with a diisopropyl fluorophosphate-sensitive trypsinlike protease from the mosquito midgut or endoproteinase Lys-C increased its enzymatic activity. These results suggest that malaria parasite has evolved an intricate mechanism to adapt to the PM and the protease-rich environment of the mosquito midgut.

Acetylglucosamine↗

Characterization and biocontrol ability of fusion chitinase in Escherichia coli carrying chitinase cDNA from Trichothecium roseum.

The antifungal mechanism of mycoparasitic fungi involves fungal cell wall degrading enzymes such as chitinases. Trichothecium roseum is an important mycoparasitic fungus with significant antifungal ability, but studies on chitinases of T. roseum were poor. Here, we report a novel chitinase cDNA isolated from T. roseum by PCR amplification based on conserved chitinase sequences. Southern blot analysis suggested that a single copy of the gene exists in the genome of T. roseum. The deduced open reading frame of 1,143 nucleotides encodes a protein of 380 amino acids with a calculated molecular weight of 41.6 kDa. The fusion chitinase expressed in Escherichia coli has been purified by single-step chromatography. It has a pI of pH 5.4 and expresses a thermal stability, but is insensitive to pH in a broad pH range. According to expectation, E. coli efficiently yielded a high amount of active chitinase. Remarkably, the fusion chitinase offered high antifungal activity.

Amino Acid Sequence↗