Chitinases catalyze the degradation of chitin, a ubiquitous polymer generated from the cell walls of fungi, shells of crustaceans, and cuticles of insects. They are gaining increasing attention in medicine, agriculture, food and drug industries, and environmental management. Their roles in the degradation of chitin for the production of industrially useful products and in the control of fungal pathogens and insect pests render them attractive for such purposes. However, chitinases have diverse sources, characteristics, and mechanisms of action that seem to restrain optimization procedures and render standardization techniques for enhanced practical applications complex. Hence, results of laboratory trials are not usually consistent with real-life applications. With the growing field of protein engineering, these complexities can be overcome by modifying or redesigning chitinases to enhance specific features required for specific applications. In this review, the variations in features and mechanisms of chitinases that limit their exploitation in biotechnological applications are compiled. Recent attempts to engineer chitinases for improved efficiency are also highlighted.
This study discusses the isolation and identification of a new Streptomycetes highly active chitinase producer. Fifteen strains were isolated from Malaysian soil samples. The isolate WICC-A03 was found to be the most active chitinase producer. Its antifungal activity was evaluated against many phytopathogens. The identification of WICC-A03 using phenotypic and genotypic methods strongly indicated that strain WICC-A03 belonged to the genus Streptomyces and displayed similarity (91%) with Streptomyces glauciniger. Thus, it was given the suggested name S. glauciniger WICC-A03 with accession number: JX139754. WICC-A03 produces extracellular chitinase in a medium containing 1.5% colloidal chitin in submerged culture on 144 h. The produced enzyme was partially characterised and its molecular weight of 50 kDa was determined by using SDS-PAGE. This study indicates that WICC-A03 is a potential chitinase producer for biocontrol of plant pathogens. Further experiments are being carried out to optimise medium composition and cultivation conditions under lab and bioreactor scale.
The 'pitchers' of carnivorous pitcher plants are exquisite examples of convergent evolution. An open question is whether the living communities housed in pitchers also converge in structure or function. Using samples from more than 330 field-collected pitchers of eight species of Southeast Asian Nepenthes and six species of North American Sarracenia, we demonstrate that the pitcher microcosms, or miniature ecosystems with complex communities, are strikingly similar. Compared to communities from surrounding habitats, pitcher communities house fewer species. While communities associated with the two genera contain different microbial organisms and arthropods, the species are predominantly from the same phylogenetic clades. Microbiomes from both genera are enriched in degradation pathways and have high abundances of key degradation enzymes. Moreover, in a manipulative field experiment, Nepenthes pitchers placed in a North American bog assembled Sarracenia-like communities. An understanding of the convergent interactions in pitcher microcosms facilitates identification of selective pressures shaping the communities.
Type A chitinases (EC 3.2.1.14), GH family 18, attack chitin ((1 → 4)-2-acetamido-2-deoxy-β-D-glucan) and chito-oligosaccharides from the reducing end to catalyze release of chitobiose (N,N'-diacetylchitobiose) via hydrolytic cleavage of N-acetyl-β-D-glucosaminide (1 → 4)-β-linkages and are thus "exo-chitobiose hydrolases." In this study, the chitinase type A from Serratia marcescens (SmaChiA) was used as a template for identifying two novel exo-chitobiose hydrolase type A enzymes, FbalChi18A and MvarChi18A, originating from the marine organisms Ferrimonas balearica and Microbulbifer variabilis, respectively. Both FbalChi18A and MvarChi18A were recombinantly expressed in Escherichia coli and were confirmed to exert exo-chitobiose hydrolase activity on chito-oligosaccharides, but differed in temperature and pH activity response profiles. Amino acid sequence comparison of the catalytic β/α barrel domain of each of the new enzymes showed individual differences, but ~69% identity of each to that of SmaChiA and highly conserved active site residues. Superposition of a model substrate on 3D structural models of the catalytic domain of the enzymes corroborated exo-chitobiose hydrolase type A activity for FbalChi18A and MvarChi18A, i.e., substrate attack from the reducing end. A main feature of both of the new enzymes was the presence of C-terminal 5/12 type carbohydrate-binding modules (SmaChiA has no C-terminal carbohydrate binding module). These new enzymes may be useful tools for utilization of chitin as an N-acetylglucosamine donor substrate via chitobiose.
Cold-adapted enzymes are proteins produced by psychrophilic organisms that display a high catalytic efficiency at extremely low temperatures. Chitin consists of the insoluble homopolysaccharide β-(1, 4)-linked N-acetylglucosamine, which is the second most abundant biopolymer found in nature. Chitinases (EC 3.2.1.14) play an important role in chitin recycling in nature. Biodegradation of chitin by the action of cold-adapted chitinases offers significant advantages in industrial applications such as the treatment of chitin-rich waste at low temperatures, the biocontrol of phytopathogens in cold environments and the biocontrol of microbial spoilage of refrigerated food.
Chitinases in terrestrial plants have been reported these are involved in heavy metal tolerance/detoxification. This is the first attempt to reveal chitinase gene (AcCHI I) and its function on metal detoxification in mangroves Aegiceras corniculatum. RT-PCR and RACE techniques were used to clone AcCHI I, while real-time quantitative PCR was employed to assess AcCHI I mRNA expressions in response to Cadmium (Cd). The deduced AcCHI I protein consists of 316 amino acids, including a signal peptide region, a chitin-binding domain (CBD) and a catalytic domain. Protein homology modeling was performed to identify potential features in AcCHI I. The CBD structure of AcCHI I might be critical for metal tolerance/homeostasis of the plant. Clear tissue-specific differences in AcCHI I expression were detected, with higher transcript levels detected in leaves. Results demonstrated that a short duration of Cd exposure (e.g., 3 days) promoted AcCHI I expression in roots. Upregulated expression was also detected in leaves under 10 mg/kg Cd concentration stress. The present study demonstrates that AcCHI I may play an important role in Cd tolerance/homeostasis in the plant. Further studies of the AcCHI I protein, gene overexpression, the promoter and upstream regulation will be necessary for clarifying the functions of AcCHI I.