Biosynthesis, Turnover, and Functions of Chitin in Insects

Abstract

Chitin is a major component of the exoskeleton and the peritrophic matrix of insects. It forms complex structures in association with different assortments of cuticle and peritrophic matrix proteins to yield biocomposites with a wide range of physicochemical and mechanical properties. The growth and development of insects are intimately coupled with the biosynthesis, turnover, and modification of chitin. The genes encoding numerous enzymes of chitin metabolism and proteins that associate with and organize chitin have been uncovered by bioinformatics analyses. Many of these proteins are encoded by sets of large gene families. There is specialization among members within each family, which function in particular tissues or developmental stages. Chitin-containing matrices are dynamically modified at every developmental stage and are under developmental and/or physiological control. A thorough understanding of the diverse processes associated with the assembly and turnover of these chitinous matrices offers many strategies to achieve selective pest control.

Structure, Catalysis, and Inhibition of OfChi-h, the Lepidoptera-exclusive Insect Chitinase

“…One of the most striking features of OfChi-h is a number of aromatic residues lining the groove starting from the far end of domain I and ending at the far end of the substrate binding cleft of domain II (Fig. 1B) Substrate Binding Cleft of OfChi-h-Although our attempts to obtain the structure of OfChi-h complexed to its substrate hexa-N-acetylchitohexaose ((GlcNAc) 6 ) failed, the structure of OfChi-h complexed to chitoheptaose ((GlcN) 7 ), a substrate analog, was obtained by soaking OfChi-h crystals with (GlcN) 7 . The structure was determined by molecular replacement using the unliganded form of OfChi-h as a searching model.…”

“…During molting and metamorphosis, lepidopteran insects secrete molting fluid, which contains three chitinases (EC 3.2.1.14, group I chitinase (ChtI), group II chitinase (ChtII) and Chi-h), one N-acetyl-Dhexosaminidase (EC 3.2.1.52, Hex), and several kinds of proteases to degrade and shed the old cuticle (6). Chitinases degrade polymeric chitin into chitobiose and chitotriose, which are then further degraded into N-acetyl-D-glucosamine (GlcNAc) by Hex (7). Compared with the extensively studied ChtI (8 -19), there is limited information about the function of ChtII and Chi-h. RNAi of SeChi-h from Spodoptera exigua led to molting deficiency and death indicating that Chi-h is indispensable for molting (17).…”

“…The crystal structures of OfChi-h and OfChi-h in complex with a substrate analog (GlcN) 7 were obtained and resolved. Through structure-based comparison as well as biochemical characterization, we demonstrate that Chi-h acts synergistically with ChtI to degrade cuticle chitin.…”

Evaluation of some insects as potential feed ingredients for ruminants: chemical composition, in vitro rumen fermentation and methane emissions

“…Further, since chitin contains nitrogenous group in the molecule it also contributes to the high proportions of NDICP and ADICP. Exoskeleton develops with the increase of age (Zhu et al, 2016) and therefore chitin proportion per unit of DM increases as well. It was shown by the higher CF, NDF, ADF, NDICP and ADICP of BSF2 as compared to those of BSF1.…”

The deduced role of a chitinase containing two nonsynergistic catalytic domains

“…They are widely distributed across the tree of life and play various vital roles (Adrangi & Faramarzi, 2013). For organisms in which chitin is a structural component, such as fungi, arthropods and nematodes, chitinases are used to remodel cell walls, cuticles and eggshells, respectively (Hartl et al, 2012;Zhu et al, 2016). In bacteria, chitinases are produced to degrade exogenous chitin for nutrients (Vaaje-Kolstad et al, 2013).…”