Chitinases from Bacteria to Human: Properties, Applications, and Future Perspectives

Abstract

Chitin is the second most plenteous polysaccharide in nature after cellulose, present in cell walls of several fungi, exoskeletons of insects, and crustacean shells. Chitin does not accumulate in the environment due to presence of bacterial chitinases, despite its abundance. These enzymes are able to degrade chitin present in the cell walls of fungi as well as the exoskeletons of insect. They have shown being the potential agents for biological control of the plant diseases caused by various pathogenic fungi and insect pests and thus can be used as an alternative to chemical pesticides. There has been steady increase in demand of chitin derivatives, obtained by action of chitinases on chitin polymer for various industrial, clinical, and pharmaceutical purposes. Hence, this review focuses on properties and applications of chitinases starting from bacteria, followed by fungi, insects, plants, and vertebrates. Designing of chitinase by applying directed laboratory evolution and rational approaches for improved catalytic activity for cost-effective field applications has also been explored.

Figure 1

Specificity of different chitinases towards chitin polymer. N-Acetyl β-glucosaminidase cleaves monomeric unit of GlcNAc from nonreducing terminal. Chitobiosidase cleaves dimeric unit of GlcNAc from nonreducing terminal. Endochitinase cleaves glycosidic bond randomly at internal sites in chitin polymer.

Figure 2

Interaction of GlcNAc dimer TIM-barrel (β/α)8 catalytic domain of family 18 bacterial endochitinase of S. marcescens: (a) Bacterial endochitinase interaction with GlcNAc dimer (blue); (b) Hydrophobic and hydrophilic regions around active site of chitinase C.

Figure 3

Industrial applications of chitinolytic enzymes.

Figure 4

A schematic diagram showing methodology of directed laboratory evolution technique for the creation of new enzymes with enhanced catalytic activity. Chitinase gene library is created by random mutagenic PCR, which randomly incorporates desired number of amino acid mutations. Then the PCR product is cloned, expressed, and screened for higher catalytic activity. For detailed methodology, kindly refer to [9, 10].