Functional analysis of active site residues of Bacillus thuringiensis WB7 chitinase by site-directed mutagenesis

Thermophilic Chitinases: Structural, Functional and Engineering Attributes for Industrial Applications

Chitin is the second most widely found natural polymer next to cellulose. Chitinases degrade the insoluble chitin to bioactive chitooligomers and monomers for various industrial applications. Based on their function, these enzymes act as biocontrol agents against pathogenic fungi and invasive pests compared with conventional chemical fungicides and insecticides. They have other functional roles in shellfish waste management, fungal protoplast generation, and Single-Cell Protein production. Among the chitinases, thermophilic and thermostable chitinases are gaining popularity in recent years, as they can withstand high temperatures and maintain the enzyme stability for longer periods. Not all chitinases are thermostable; hence, tailor-made thermophilic chitinases are designed to enhance their thermostability by direct evolution, genetic engineering involving mutagenesis, and proteomics approach. Although research has been done extensively on cloning and expression of thermophilic chitinase genes, there are only few papers discussing on the mechanism of chitin degradation using thermophiles. The current review discusses the sources of thermophilic chitinases, improvement of protein stability by gene manipulation, metagenomics approaches, chitin degradation mechanism in thermophiles, and their prospective applications for industrial, agricultural, and pharmaceutical purposes.

Oligomer Formation and Insecticidal Activity of Bacillus thuringiensis Vip3Aa Toxin

Bacillus thuringiensis (Bt) Vip3A proteins are important insecticidal proteins used for control of lepidopteran insects. However, the mode of action of Vip3A toxin is still unclear. In this study, the amino acid residue S164 in Vip3Aa was identified to be critical for the toxicity in Spodoptera litura. Results from substitution mutations of the S164 indicate that the insecticidal activity of Vip3Aa correlated with the formation of a >240 kDa complex of the toxin upon proteolytic activation. The >240 kDa complex was found to be composed of the 19 kDa and the 65 kDa fragments of Vip3Aa. Substitution of the S164 in Vip3Aa protein with Ala or Pro resulted in loss of the >240 kDa complex and loss of toxicity in Spodoptera litura. In contrast, substitution of S164 with Thr did not affect the >240 kDa complex formation, and the toxicity of the mutant was only reduced by 35%. Therefore, the results from this study indicated that formation of the >240 kDa complex correlates with the toxicity of Vip3Aa in insects and the residue S164 is important for the formation of the complex.

In vitro engineering of microbial enzymes with multifarious applications: prospects and perspectives

The discovery of a novel enzyme from a microbial source takes anywhere between months to years, and therefore, there has been an immense interest in modifying the existing microbial enzymes to suit the present day needs of the industry. The redesigning of industrially useful enzymes for improving their performance has become a challenge because bioinformatics databases have been revealing new facts on a day-to-day basis. Modification of the existing enzymes has become a trend for fine tuning of biocatalysts in the biotech industry. Hydrolases are employed in pharmaceutical, biofuel, detergent, food and feed industries that significantly contribute to the global annual revenue, and therefore, the emphasis has been on engineering them. Although a large data is accumulating on making alterations in microbial enzymes, there is a lack of definite information on redesigning industrial enzymes. This review focuses on the recent developments in improving the characteristics of various biotechnologically important enzymes.

Biotechnological approaches to develop bacterial chitinases as a bioshield against fungal diseases of plants

Fungal diseases of plants continue to contribute to heavy crop losses in spite of the best control efforts of plant pathologists. Breeding for disease-resistant varieties and the application of synthetic chemical fungicides are the most widely accepted approaches in plant disease management. An alternative approach to avoid the undesired effects of chemical control could be biological control using antifungal bacteria that exhibit a direct action against fungal pathogens. Several biocontrol agents, with specific fungal targets, have been registered and released in the commercial market with different fungal pathogens as targets. However, these have not yet achieved their full commercial potential due to the inherent limitations in the use of living organisms, such as relatively short shelf life of the products and inconsistent performance in the field. Different mechanisms of action have been identified in microbial biocontrol of fungal plant diseases including competition for space or nutrients, production of antifungal metabolites, and secretion of hydrolytic enzymes such as chitinases and glucanases. This review focuses on the bacterial chitinases that hydrolyze the chitinous fungal cell wall, which is the most important targeted structural component of fungal pathogens. The application of the hydrolytic enzyme preparations, devoid of live bacteria, could be more efficacious in fungal control strategies. This approach, however, is still in its infancy, due to prohibitive production costs. Here, we critically examine available sources of bacterial chitinases and the approaches to improve enzymatic properties using biotechnological tools. We project that the combination of microbial and recombinant DNA technologies will yield more effective environment-friendly products of bacterial chitinases to control fungal diseases of crops.