Chito-Protein Matrices in Arthropod Exoskeletons and Peritrophic Matrices

Abstract

The exoskeleton of an arthropod is formed by layered cuticles that are mainly composed of chitin and associated proteins in form of chito-protein matrices. Some internal organs of an arthropod, such as digestive tract and tracheal system, also contain chitin. Chitin biosynthesis is crucial for arthropod growth and development as the cuticular exoskeleton is regularly shed and replaced by a new cuticle. The biosynthesis starts by polymerizing N-acetylglucosamine (GlcNAc) units into a chitin polymer by chitin synthases. Chitin polymers are then translocated across the plasma membrane to form chitin microfibrils. Partial deacetylation of chitin polymers by chitin deacetylases facilitates a helicoidal arrangement of chitin layers. Numerous chitin-binding proteins are involved in the formation of chito-protein matrices both in the cuticle and peritrophic matrix (PM) of the midgut. These proteins influence the overall mechanical and physicochemical properties of the matrices. Chitin degradation is catalyzed by a two-component chitinolytic enzyme system, including the hydrolysis of chitin polymers into chitin oligomers by chitinases and the hydrolysis of the oligomers into monomeric GlcNAc by β-N-acetylglucosaminidases. Because chitin biosynthesis, modification, translocation, deposition, assembly, and degradation are highly complex biological processes, detailed mechanisms of many steps are still not fully understood. Nevertheless, chitin and chitosan (highly deacetylated chitin) have been commonly used as biomaterials due to their excellent properties including the biocompatibility, biodegradability, non-toxicity, and adsorption. Because plants and vertebrates including humans lack chitin biosynthesis, various approaches have been utilized for relatively safe control of arthropod pests by targeting their chitin biosynthetic and metabolic pathways.