Chitinase genes LbCHI31 and LbCHI32 from Limonium bicolor were successfully expressed in Escherichia coli and exhibit recombinant chitinase activities

A High-Throughput Screening System Based on Fluorescence-Activated Cell Sorting for the Directed Evolution of Chitinase A

Chitinases catalyze the degradation of chitin, a polymer of N-acetylglucosamine found in crustacean shells, insect cuticles, and fungal cell walls. There is great interest in the development of improved chitinases to address the environmental burden of chitin waste from the food processing industry as well as the potential medical, agricultural, and industrial uses of partially deacetylated chitin (chitosan) and its products (chito-oligosaccharides). The depolymerization of chitin can be achieved using chemical and physical treatments, but an enzymatic process would be more environmentally friendly and more sustainable. However, chitinases are slow-acting enzymes, limiting their biotechnological exploitation, although this can be overcome by molecular evolution approaches to enhance the features required for specific applications. The two main goals of this study were the development of a high-throughput screening system for chitinase activity (which could be extrapolated to other hydrolytic enzymes), and the deployment of this new method to select improved chitinase variants. We therefore cloned and expressed the Bacillus licheniformis DSM8785 chitinase A (chiA) gene in Escherichia coli BL21 (DE3) cells and generated a mutant library by error-prone PCR. We then developed a screening method based on fluorescence-activated cell sorting (FACS) using the model substrate 4-methylumbelliferyl β-d-N,N′,N″-triacetyl chitotrioside to identify improved enzymes. We prevented cross-talk between emulsion compartments caused by the hydrophobicity of 4-methylumbelliferone, the fluorescent product of the enzymatic reaction, by incorporating cyclodextrins into the aqueous phases. We also addressed the toxicity of long-term chiA expression in E. coli by limiting the reaction time. We identified 12 mutants containing 2–8 mutations per gene resulting in up to twofold higher activity than wild-type ChiA.

Analysis of glycoside hydrolases from oat (Avena sativa) seedling extract

The abundance and the diversity of oligo- and polysaccharides provide a wide range of biological roles attributed either to these carbohydrates or to their relevant enzymes, i.e., the glycoside hydrolases (GHs). The biocatalysis by these families of enzymes is highly attractive for the generation of products used in potential applications, e.g., pharmaceuticals and food industries. It is thus very important to extract and characterize such enzymes, particularly from plant tissues. In this study, we characterized novel sequences of class I chitinases from seedlings extract of the common oat (Avena sativa L.) using proteomics and sequence-structure-function analysis. These enzymes, which belong to the GH19 family of protein, were extracted from oat and identified using SDS-PAGE, trypsin digestion, LC-MS-MS, and sequence-structure-function analysis. The amino acid sequences of the oat tryptic peptides were used to identify cDNAs from the Avena sativa databases of the expressed sequence tags (ESTs) and transcriptome shotgun assembly (TSA). Based upon the Avena sativa sequences of ESTs and TSA, at least 4 predicted genes that encoded oat class I chitinases were identified and reported. The structural characterization of the oat sequences of chitinases provided valuable insights to the context.

Improved antifungal activity of barley derived chitinase I gene that overexpress a 32kDa recombinant chitinase in Escherichia coli host

Agricultural crops suffer many diseases, including fungal and bacterial infections, causing significant yield losses. The identification and characterisation of pathogenesis-related protein genes, such as chitinases, can lead to reduction in pathogen growth, thereby increasing tolerance against fungal pathogens. In the present study, the chitinase I gene was isolated from the genomic DNA of Barley (Hordeum vulgare L.) cultivar, Haider-93. The isolated DNA was used as template for the amplification of the ∼935bp full-length chitinase I gene. Based on the sequence of the amplified gene fragment, class I barley chitinase shares 93% amino acid sequence homology with class II wheat chitinase. Interestingly, barley class I chitinase and class II chitinase do not share sequence homology. Furthermore, the amplified fragment was expressed in Escherichia coli Rosetta strain under the control of T7 promoter in pET 30a vector. Recombinant chitinase protein of 35kDa exhibited highest expression at 0.5mM concentration of IPTG. Expressed recombinant protein of 35kDa was purified to homogeneity with affinity chromatography. Following purification, a Western blot assay for recombinant chitinase protein measuring 35kDa was developed with His-tag specific antibodies. The purified recombinant chitinase protein was demonstrated to inhibit significantly the important phytopathogenic fungi Alternaria solani, Fusarium spp, Rhizoctonia solani and Verticillium dahliae compared to the control at concentrations of 80μg and 200μg.

Recombinant exochitinase of the thermophilic mould Myceliopthora thermophila BJA: Characteristics and utility in generating N-acetyl glucosamine and in biocontrol of phytopathogenic fungi

Chitinase from the thermophilic mould Myceliopthora thermophila BJA (MtChit) is an acid tolerant, thermostable and organic solvent stable biocatalyst which does not require any metal ions for its activity. To produce high enzyme titres, reduce fermentation time and overcome the need for induction, this enzyme has been heterologously expressed under GAP promoter in the GRAS yeast, Pichia pastoris. The production medium supplemented with the permeabilizing agent Tween-20 supported two-fold higher rMtChit production (5.5 × 10³ U L^-1 ). The consensus sequences S(132)xG(133)G(134) and D(168)xxD(171)xD(173)xE(175) in the enzyme have been found to represent the substrate binding and catalytic sites, respectively. The rMtChit, purified to homogeneity by a two-step purification strategy, is a monomeric glycoprotein of ∼48 kDa, which is optimally active at 55°C and pH 5.0. The enzyme is thermostable with t_1/2 values of 113 and 48 min at 65 and 75°C, respectively. Kinetic parameters K_m , V_max , k_cat , and k_cat /K_m of the enzyme are 4.655 mg mL^-1 , 34.246 nmol mg^-1  s^-1 , 3.425 × 10⁶ min^-1 , and 1.36 × 10^-6 mg mL^-1  min^-1 , respectively. rMtChit is an unique exochitinase, since its action on chitin liberates N-acetylglucosamine NAG. The enzyme inhibits the growth of phytopathogenic fungi like Fusarium oxysporum and Curvularia lunata, therefore, this finds application as biofungicide at high temperatures during summer in tropics. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 33:70-80, 2017.