Chitin contributes to the rigidity of the insect cuticle and serves as an attachment matrix for other cuticular proteins. Deficiency of chitin results in abnormal embryos, cuticular structural defects and growth arrest. When chitin is not turned over during molting, the developing insect is trapped inside the old cuticle. Partial deacetylation of cuticular chitin is also required for proper laminar organization of the cuticle and vertical pore canals, molting, and locomotion. Thus, chitin and its modifications strongly influence the structure of the exoskeleton as well as the physiological functions of the insect. Internal tendons and specialized epithelial cells called "tendon cells" that arise from the outer layer of epidermal cells provide attachment sites at both ends of adult limb muscles. Membrane processes emanating from both tendon and muscle cells interdigitate extensively to strengthen the attachment of muscles to the extracellular matrix (ECM). Protein ligands that bind to membrane-bound integrin complexes further enhance the adhesion between muscles and tendons. Tendon cells contain F-actin fiber arrays that contribute to their rigidity. In the cytoplasm of muscle cells, proteins such as talin and other proteins provide attachment sites for cytoskeletal actin, thereby increasing integrin binding and activation to mechanically couple the ECM with actin in muscle cells. Mutations in integrins and their ligands, as well as depletion of chitin deacetylases, result in defective locomotion and muscle detachment from the ECM. Thus, chitin in the cuticle and chitin deacetylases strongly influence the shape and functions of the exoskeleton as well as locomotion of insects.

Insect Cuticular Chitin Contributes to Form and Function.

Tuning chitosan's chemical structure for enhanced biological functions.

OfChi-h, a lepidopteran-exclusive glycoside hydrolase family 18 (GH18) chitinase from the agricultural insect pest Ostrinia furnacalis, is a promising molecular target candidate for pest control and management. Berberine (BER), a traditional Chinese medicine, binds to a wide variety of glycosyl hydrolases via an identical mechanism, showing potential as a pesticide lead compound. In this work, we found that BER was a moderate inhibitor of OfChi-h with a Ki of 16.1 μM. To improve its efficacy, a series of BER derivatives featuring an ester bond linked to an aromatic or heterocyclic aromatic ring at the 9-position were designed and evaluated as effective OfChi-h inhibitors. The most potent compound, compound 19e with a nicotinate group, exhibited a Ki of 0.093 μM. Molecular docking analysis suggested that the common binding mode of BER derivatives featured a network of π-π stacking and electrostatic interactions and that the group at the 9-position enhanced the van der Waals and hydrogen bonding interactions. Administration of the BER derivative 19c to 4th-instar O. furnacalis larvae in an artificial diet led to their impaired growth and metamorphosis. This work provides a new starting point for the modification of BER for use in pest control.

Novel Inhibitors of an Insect Pest Chitinase: Design and Optimization of 9-O-Aromatic and Heterocyclic Esters of Berberine.

Enzymatic hydrolysis of crystalline chitin is a solid–liquid interfacial catalysis process that is highly dependent on the enzymes’ processivity, namely, the number of catalytic cycles consecutivel...

High-Speed Atomic Force Microscopy Reveals Factors Affecting the Processivity of Chitinases during Interfacial Enzymatic Hydrolysis of Crystalline Chitin

Chitin is one of the most abundant and renewable natural biopolymers. It exists in the form of crystalline microfibrils and is the basic structural building block of many biological materials. Its surface crystalline structure is yet to be reported at the molecular level. Herein, atomic force microscopy (AFM) in combination with molecular dynamics simulations reveals the molecular‐scale structural details of the chitin nanocrystal (chitin NC)–water interface. High‐resolution AFM images reveal the molecular details of chitin chain arrangements at the surfaces of individual chitin NCs, showing highly ordered, stable crystalline structures almost free of structural defects or disorder. 3D‐AFM measurements with submolecular spatial resolution demonstrate that chitin NC surfaces interact strongly with interfacial water molecules creating stable, well‐ordered hydration layers. Inhomogeneous encapsulation of the underlying chitin substrate by these hydration layers reflects the chitin NCs’ multifaceted surface character with different chain arrangements and molecular packing. These findings provide important insights into chitin NC structures at the molecular level, which is critical for developing the properties of chitin‐based nanomaterials. Furthermore, these results will contribute to a better understanding of the chemical and enzymatic hydrolysis of chitin and other native polysaccharides, which is also essential for the enzymatic conversion of biomass.

Probing the Structural Details of Chitin Nanocrystal–Water Interfaces by Three‐Dimensional Atomic Force Microscopy

The insect group II chitinase (ChtII, also known as Cht10) is a unique chitinase with multiple catalytic and chitin binding domains. It has been proved to be an essential chitinase for molting genetically. However, ChtII's role in chitin degradation during insect development remains poorly understood. Obtaining this knowledge is the key to fully understanding the chitin degradation system in insect. Here, we investigated the role of OfChtII during the molting of Ostrinia furnacalis, a model lepidopteran pest insect. OfChtII was expressed earlier than OfChtI (OfCht5) and OfChi-h, at both the gene and protein levels during larva-pupa molting as evidenced by qPCR and western blot analyses. A truncated OfChtII, OfChtII-B4C1, was recombinantly expressed in Pichia pastoris cells and purified to homogeneous. The recombinant OfChtII-B4C1 loosened compacted chitin particles and produced holes in the cuticle surface as evidenced by scanning electron microscopy. It synergized with OfChtI and OfChi-h when hydrolyzing insoluble α-chitin. These findings suggested an important role for ChtII during insect molting and also provided a strategy for the coordinated degradation of the cuticular chitin during insect molting by ChtII, ChtI and Chi-h. This article is protected by copyright. All rights reserved.

Insect group II chitinase OfChtII promotes chitin degradation during larva-pupa molting.

The invention discloses application of recombinant chitinase to an insecticidal or bacterium-inhibition effect. The recombinant chitinase is recombinant chitinase ChtII-B4Cl which only exists in insects and has a multi-structure domain; an experiment proves a new effect of the recombinant chitinase to the aspect of biologically preventing and controlling diseases and insect pests; the recombinantchitinase has an insecticidal effect on frankliniella occidentalis; furthermore, the experiment also proves that the recombinant chitinase has good bacterium-inhibition activity on colletotrichum capsici, alternaria solani, curvulavia lunata and the like and shows that the chitinase ChtII-B4Cl has the bacterium-inhibition and insecticidal activity; the recombinant chitinase plays an important roleand has application value in the aspect of biologically preventing and controlling the diseases and insect pests in the field of agriculture.

Application of recombinant chitinase to insecticidal or bacterium-inhibition effect

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Insect group II chitinase OfChtII promotes chitin degradation during larva-pupa molting.

High-Speed Atomic Force Microscopy Reveals Factors Affecting the Processivity of Chitinases during Interfacial Enzymatic Hydrolysis of Crystalline Chitin

Application of recombinant chitinase to insecticidal or bacterium-inhibition effect