Molecular cloning and functional expression of chitinase-encoding cDNA from the cabbage moth, Mamestra brassicae

Functional expression of recombinant hybrid enzymes composed of bacterial and insect's chitinase domains in E. coli

To elucidate the functional alteration of the recombinant hybrid chitinases composed of bacterial and insect's domains, we cloned the constitutional domains from chitinase-encoding cDNAs of a bacterial species, Bacillus thuringiensis (BtChi) and a lepidopteran insect species, Mamestra brassicae (MbChi), respectively, swapped one's leading signal peptide (LSP) - catalytic domain (CD) - linker region (LR) (LCL) with the other's chitin binding domain (ChBD) between the two species, and confirmed and analyzed the functional expression of the recombinant hybrid chitinases and their chitinolytic activities in the transformed E. coli strains. Each of the two recombinant cDNAs, MbChi's LCL connected with BtChi's ChBD (MbLCL-BtChBD) and BtChi's LCL connected with MbChi's ChBD (BtLCL-MbChBD), was successfully introduced and expressed in E. coli BL21 strain. Although both of the two hybrid enzymes were found to be expressed by SDS-PAGE and Western blotting, the effects of the introduced genes on the chitin metabolism appear to be dramatically different between the two transformed E. coli strains. BtLCL-MbChBD remarkably increased not only the cell proliferation rate, extracellular and cellular chitinolytic activity, but also cellular glucosamine and N-acetylglucosamine levels, while MbLCL-BtChBD showed about the same profiles in the three tested subjects as those of the strains transformed with each of the two native chitinases, indicating that a combination of the bacterial CD of TIM barrel structure with characteristic six cysteine residues and insect ChBD2 including a conserved six cysteine-rich region (6C) enhances the attachment of the enzyme molecule to chitin compound by MbChBD, and so increases the catalytic efficiency of bacterial CD.

Functional expression of the Spodoptera exigua chitinase to examine the virtually screened inhibitor candidates

Chitinase is responsible for insect chitin hydrolyzation, which is a key process in insect molting and pupation. However, little is known about the chitinase of Spodoptera exigua (SeChi). In this study, based on the SeChi gene (ADI24346) identified in our laboratory, we constructed the recombinant baculovirus P-Chi for the expression of recombinant SeChi (rSeChi) in Hi5 cells. The rSeChi was purified by chelate affinity chromatography, and the purified protein showed activity comparable with that of a commercial SgChi, suggesting that we harvested active SeChi for the first time. The purified protein was subsequently tested for enzymatic properties and revealed to exhibit its highest activity at pH 8 and 40 C. Using homology modeling and molecular docking techniques, the three-dimensional model of SeChi was constructed and screened for inhibitors. In two rounds of screening, twenty compounds were selected. With the purified rSeChi, we tested each of the twenty compounds for inhibitor activity against rSeChi, and seven compounds showed obvious activity. This study provided new information for the chitinase of beet armyworm and for chitinase inhibitor development.

Functional analysis of eight chitinase genes in rice stem borer and their potential application in pest control

Insect chitinases participate in numerous physiological processes such as nutrition, parasitism, morphogenesis and immunity. These properties make chitinases good targets for pest control. Rice striped stem borer (SSB), Chilo suppressalis Walker, is one of the most destructive pests of rice causing huge yield losses. In our previous work, we reported the identification of 12 SSB chitinase (CsCht) genes, and studied the functions of CsCht1 to 4. Here, we have extended our study to investigate the expression patterns and functions of CsCht5 to 12. All eight chitinase genes displayed distinct temporospatial expression profiles. We looked at the effect of knocking down each gene at the developmental stage where highest expression was observed. Knocking down CsCht5, CsCht6 and CsCht8 resulted in high mortality and delayed development. Although silencing CsCht7, CsCht9, CsCht10, CsCht11 and CsCht12 had no apparent effect on development, knocking down CsCht10 in SSB individuals that were simultaneously treated with Beauveria bassiana (Bb84) led to higher mortality rates and quicker death, suggesting CsCht10 has an essential role in protecting SSB from exogenous microorganisms. In summary, we elucidated the functions of eight SSB chitinase genes and found that CsCht10 could be a good candidate for pest control.

Cloning, Site-Directed Mutagenesis, and Functional Analysis of Active Residues in Lymantria dispar Chitinase

Chitinases are glycosyl hydrolases that catalyze the hydrolysis of β-(1,4)-glycosidic bonds in chitin, the major structural polysaccharide presented in the cuticle and gut peritrophic matrix of insects. Two aspartate residues (D143, D145) and one tryptophan (W146) in the Lymantria dispar chitinase are highly conserved residues observed within the second conserved motif of the family 18 chitinase catalytic region. In this study, a chitinase cDNA, LdCht5, was cloned from L. dispar, and the roles of the three residues were investigated using site-directed mutagenesis and substituting them with three other amino acids. Seven mutant proteins, D143E, D145E, W146G, D143E/D145E, D143E/W146G, D145E/W146G, and D143E/D145E/W146G, as well as the wild-type enzyme, were produced using the baculovirus-insect cell line expression system. The enzymatic and kinetic properties of these mutant enzymes were measured using the oligosaccharide substrate MU-(GlcNAc)₃. Among the seven mutants, the D145E, D143E/D145E, and D145E/W146G mutations kept some extant catalytic activity toward MU-(GlcNAc)₃, while the D143E, W146G, D143E/W146G, and D143E/D145E/W146G mutant enzymes were inactivated. Compared with the mutant enzymes, the wild-type enzyme had higher values of k _cat and k _cat / K _m . A study of the multiple point mutations in the second conserved catalytic region would help to elucidate the role of the critical residues and their relationships.

Structure, Catalysis, and Inhibition of OfChi-h, the Lepidoptera-exclusive Insect Chitinase

Chitinase-h (Chi-h) is of special interest among insect chitinases due to its exclusive distribution in lepidopteran insects and high sequence identity with bacterial and baculovirus homologs. Here OfChi-h, a Chi-h from Ostrinia furnacalis, was investigated. Crystal structures of both OfChi-h and its complex with chitoheptaose ((GlcN)₇) reveal that OfChi-h possesses a long and asymmetric substrate binding cleft, which is a typical characteristics of a processive exo-chitinase. The structural comparison between OfChi-h and its bacterial homolog SmChiA uncovered two phenylalanine-to-tryptophan site variants in OfChi-h at subsites +2 and possibly -7. The F232W/F396W double mutant endowed SmChiA with higher hydrolytic activities toward insoluble substrates, such as insect cuticle, α-chitin, and chitin nanowhisker. An enzymatic assay demonstrated that OfChi-h outperformed OfChtI, an insect endo-chitinase, toward the insoluble substrates, but showed lower activity toward the soluble substrate ethylene glycol chitin. Furthermore, OfChi-h was found to be inhibited by N,N',N″-trimethylglucosamine-N,N',N″,N″'-tetraacetylchitotetraose (TMG-(GlcNAc)₄), a substrate analog which can be degraded into TMG-(GlcNAc)_1-2 Injection of TMG-(GlcNAc)₄ into 5th-instar O. furnacalis larvae led to severe defects in pupation. This work provides insights into a molting-indispensable insect chitinase that is phylogenetically closer to bacterial chitinases than insect chitinases.

Genome-wide analysis of chitinase genes and their varied functions in larval moult, pupation and eclosion in the rice striped stem borer, Chilo suppressalis

Some insect chitinases are required to degrade chitin and ensure successful metamorphosis. Although chitinase genes have been well characterized in several model insects, no reports exist for the rice striped stem borer, Chilo suppressalis, a highly destructive pest that causes huge yield losses in rice production. Here, we conducted a genome-level analysis of chitinase genes in C. suppressalis. After amplification of full-length transcripts with rapid amplification of cDNA ends, we identified 12 chitinase genes in C. suppressalis. All these genes had the conserved domains and motifs of glycoside hydrolase family 18 and grouped phylogenetically into five subgroups. C. suppressalis chitinase 1 (CsCht1) was highly expressed in late pupae, whereas CsCht3 was abundant in early pupae. Both CsCht2 and CsCht4 were highly expressed in larvae. CsCht2 was abundant specifically in the third-instar larvae and CsCht4 showed periodic high expression in 2- to 5-day-old larvae in each instar. Tissue specific expression analysis indicated that CsCht1 and CsCht3 were highly expressed in epidermis whereas CsCht2 and CsCht4 were specifically abundant in the midgut. Knockdown of CsCht1 resulted in adults with curled wings, indicating that CsCht1 might have an important role in wing expansion. Silencing of CsCht2 or CsCht4 arrested moulting, suggesting essential roles in larval development. When the expression of CsCht3 was interfered, defects in pupation occurred. Overall, we provide here the first catalogue of chitinase genes in the rice striped stem borer and have elucidated the functions of four chitinases in metamorphosis.

Heterologous expression and characterization of two chitinase 5 enzymes from the migratory locust Locusta migratoria

Insect chitinases are involved in degradation of chitin from the exoskeleton or peritrophic metrix of midgut. In Locusta migratoria, two duplicated Cht5s (LmCht5-1 and LmCht5-2) have been shown to have distinct molecular characteristics and biological roles. To explore the protein properties of the two LmCht5s, we heterologously expressed both enzymes using baculovirus expression system in SF9 cells, and characterized kinetic and carbohydrate-binding properties of purified enzymes. LmCht5-1 and LmCht5-2 exhibited similar pH and temperature optimums. LmCht5-1 has lower Km value for the oligomeric substrate (4MU-(GlcNAc)3 ), and higher Km value for the longer substrate (CM-Chitin-RBV) compared with LmCht5-2. A comparison of amino acids and homology modeling of catalytic domain presented similar TIM barrel structures and differentiated amino acids between two proteins. LmCht5-1 has a chitin-binding domain (CBD) tightly bound to colloidal chitin, but LmCht5-2 does not have a CBD for binding to colloidal chitin. Our results suggested both LmCht5-1 and LmCht5-2, which have the critical glutamate residue in region II of catalytic domain, exhibited chitinolytic activity cleaving both polymeric and oligomeric substrates. LmCht5-1 had relatively higher activity against the oligomeric substrate, 4MU-(GlcNAc)3 , whereas LmCht5-2 exhibited higher activity toward the longer substrate, CM-Chitin-RBV. These findings are helpful for further research to clarify their different roles in insect growth and development.

Cloning and functional expression of a chitinase cDNA from the apple leaf miner moth Lithocolletis ringoniella

Insect chitinase plays essential roles in chitin catabolism involved in digestion and molting during insect development. In the current work, we cloned a chitinase cDNA, LrCht5, from the apple leaf miner moth Lithocolletis ringoniella and characterized its amino acid sequence and protein properties. The L. ringoniella chitinase cDNA was 2136 bp in length with an open reading frame of 1737 bp that encodes a polypeptide of 579 amino acid residues with a predicted molecular mass of 64.4 kDa and pI of 5.49. The catalytic domain has several phosphorylation and glycosylation sites. The recombinant LrCht5 was expressed in Escherichia coli and the Spodoptera frugiperda cell line Sf9, and the LrCht5 expressed in insect cells exhibited chitinolytic activity. LrCht5 was most stable at pH 6.0 and 45°C. This work has potential application in the development of novel and more specific synthetic chitinase inhibitors for use as bioinsecticides.

Two chitinase 5 genes from Locusta migratoria: molecular characteristics and functional differentiation

The duplication of chitinase 5 (Cht5) into two to five different genes has been reported only in mosquito species to date. Here, we report the duplication of Cht5 genes (LmCht5-1 and LmCht5-2) in the migratory locust (Locusta migratoria). Both LmCht5-1 (505 aa) and LmCht5-2 (492 aa) possess a signal peptide and a catalytic domain with four conserved motifs, but only LmCht5-1 contains a chitin-binding domain. Structural and phylogenetic analyses suggest that LmCht5-1 is orthologous to other insect Cht5 genes, whereas LmCht5-2 might be newly duplicated. Both LmCht5 genes were expressed in all tested tissues with LmCht5-1 highly expressed in hindgut and LmCht5-2 highly expressed in integument, foregut, hindgut and fat bodies. From the fourth-instar nymphs to the adults, LmCht5-1 and LmCht5-2 showed similar developmental expression patterns with transcript peaks prior to each nymphal molting, suggesting that their expression levels are similarly regulated. Treatment with 20-hydroxyecdysone (20E; the most active molting hormone) and reducing expression of EcR (ecdysone receptor gene) by RNAi increased and decreased expression of both LmCht5 genes, respectively, indicating that both genes are responsive to 20E. Although transcript level of LmCht5-2 is generally 10-fold higher than that of LmCht5-1, RNAi-mediated suppression of LmCht5-1 transcript led to severe molting defects and lethality, but such effects were not seen with RNAi of LmCht5-2, suggesting that the newly duplicated LmCht5-2 is not essential for development and survivorship of the locust.