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Event: 1522

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Inhibition, Chitin synthase 1

Short name

The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help

Inhibition, CHS-1

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Biological Context

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Level of Biological Organization
Molecular

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place. For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable. For individual/population events, the organ context is not applicable. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Cell term
cuticle secreting cell

Organ term

Organ term
epithelium

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; https://aopwiki.org/info_pages/2/info_linked_pages/7#List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor). Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Process	Object	Action
chitin synthase activity		decreased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE. Clicking on the name of the AOP will bring you to the individual page for that AOP. More help

AOP Name	Role of event in AOP	Point of Contact	Author Status	OECD Status
SAM depletion leading to population decline (1)	MolecularInitiatingEvent	Agnes Aggy (send email)	Under development: Not open for comment. Do not cite
CHS-1 inhibition leading to mortality	MolecularInitiatingEvent	Brendan Ferreri-Hanberry (send email)	Open for citation & comment	WPHA/WNT Endorsed

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help

Term	Scientific Term	Evidence	Link
Anopheles gambiae	Anopheles gambiae	High	NCBI
Tribolium castaneum	Tribolium castaneum	High	NCBI
Trichoplusia ni	Trichoplusia ni	High	NCBI
Hyalophora cecropia	Hyalophora cecropia	High	NCBI
Bradysia hygida	Bradysia hygida	Moderate	NCBI
Mamestra brassicae	Mamestra brassicae	Moderate	NCBI
Chilo suppressalis	Chilo suppressalis	Moderate	NCBI
Locusta migratoria	Locusta migratoria	Moderate	NCBI
Nilaparvata lugens	Nilaparvata lugens	Moderate	NCBI
Aphis glycines	Aphis glycines	Moderate	NCBI
Lepeophtheirus salmonis	Lepeophtheirus salmonis	Moderate	NCBI
Panonychus citri	Panonychus citri	Moderate	NCBI
Grapholita molesta	Grapholita molesta	Moderate	NCBI
Ectropis obliqua	Ectropis obliqua	Moderate	NCBI
Tigriopus japonicus	Tigriopus japonicus	Moderate	NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help

Life stage	Evidence
Larvae	High
Juvenile	High
Adult	Moderate

Sex Applicability

An indication of the the relevant sex for this KE. More help

Term	Evidence
Unspecific	Moderate

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

Chitin synthases are essential enzymes for all organisms synthesizing chitin, for example arthropods and fungi (Latgé 2007; Merzendorfer 2011). Chitin synthases polymerize chitin and subsequently translocate chitin through the cell membrane (Merzendorfer 2006; Merzendorfer 2011). In arthropods, two isoforms of the chitin synthase are known, CHS1, which is responsible for the synthesis of cuticular chitin, and chitin synthase isoform 2, which synthesizes chitin in the midgut (Arakane et al. 2005). In this MIE, inhibition of CHS-1 is characterized. The biological state being measured is the activity of the enzyme. CHS-1 has an essential role in the cuticle biology, as it constitutes the last and most critical step in the chitin biosynthetic pathway by catalyzing the polymerization of UDP-GlcNAc to chitin (Merzendorfer and Zimoch 2003; Merzendorfer 2006).

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

Since the purification or even recombinant production of CHS-1 has not been achieved yet, the most common way is to use crude enzyme preparations for CHS-1 activity assays. It is noteworthy that in crude enzyme preparations of whole organisms both CHS isoforms, CHS-1 and CHS-2, are present. However, the expression of CHS-1 was shown to be much higher than CHS-2 in Anopheles gambiae (Zhang et al. 2012), therefore the effect of CHS-2 may be regarded as negligible. Alternatively, the digestive tract of the respective organism could be removed before producing the enzyme preparation. Different ways exist to detect the activity of the enzyme. One can incubate the enzyme preparation with radioactively labelled chitin precursors (e.g. 14C-UDP-GlcNAc) and measure radioactivity in the formed chitin chains by scintillation counting (Cohen 1982; Cohen and Casida 1990). Chitin synthase activity can also be measured in a non-radioactive way after the addition of precursors to a crude enzyme extract. There, the detection of CHS-1 activity involves the binding of chitin chains to wheat germ agglutinin (WGA) which possesses specific chitin binding properties (Lucero et al. 2002; Zhang and Yan Zhu 2013). The assay builds on the principle of a sandwich-ELISA, where chitin binds to a layer of WGA. A second layer of WGA which is conjugated to horseradish peroxidase (HRP) is then added and subsequently incubated with a HRP substrate. The cleavage of the HRP substrate leads to color formation and the amount of chitin synthesized can be determined colorimetrically.

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided). More help

Taxonomic: Effect data for the occurrence of CHS1 inhibition exist from Dipteran, Lepidopteran and Coleopteran insect species. Sequence alignment of CHS1 protein sequences using the Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS, https://seqapass.epa.gov/seqapass) tool, yielded susceptibility predictions for various insect species, arachnids and crustacean taxa such as branchiopods, hexanauplia, malocostraca and merostomata. However, most of the protein sequences were not identified as CHS1. The alignment of amino acid residues believed to be critical for ligand binding were therefore carried out with sequences identified as CHS1. Evidence was rated as high for species with a susceptibility prediction and effect data. Evidence was rated as moderate when only alignment data were available. Although most of the sequences are not annotated as CHS1, all arthropods rely on the synthesis of cuticular chitin therefore it is extremely likely that this MIE is applicable to the whole phylum of arthropods.

Life stage: This MIE is applicable for organisms undergoing continuous molt cycles. Namely larval stages of insects and all life stages of crustaceans and arachnids.

Sex: The MIE is applicable to all sexes.

Chemical: Substances known to trigger inhibit CHS-1 are of the family of pyrimidine nucleosides (e.g. polyoxin D, polyoxin B and nikkomycin Z) (Cohen and Casida 1982; Kuwano and Cohen 1984; Cohen and Casida 1990; Zhang and Yan Zhu 2013; Osada 2019). There also exists evidence for the phthalimide captan to inhibit CHS-1 activity in vitro (Cohen and Casida 1982). However, as phthalimides are known to covalently bind to thiol groups in proteins (Lukens and Sisler 1958), it is not clear if the inhibition is due to specific CHS-1 inhibition or due to unspecific protein binding.

References

List of the literature that was cited for this KE description. More help

Arakane Y, Muthukrishnan S, Kramer KJ, Specht CA, Tomoyasu Y, Lorenzen MD, Kanost M, Beeman RW. 2005. The Tribolium chitin synthase genes TcCHS1 and TcCHS2 are specialized for synthesis of epidermal cuticle and midgut peritrophic matrix. Insect Mol Biol. 14(5):453–463. doi:10.1111/j.1365-2583.2005.00576.x.

Cohen E. 1982. In vitro chitin synthesis in an insect: formation and structure of microfibrils. Eur J Cell Biol. 26(2):289–294.

Cohen E, Casida JE. 1982. Properties and inhibition of insect integumental chitin synthetase. Pestic Biochem Physiol. 17(3):301–306. doi:10.1016/0048-3575(82)90141-9.

Cohen E, Casida JE. 1990. Insect and Fungal Chitin Synthetase Activity: Specificity of Lectins as Enhancers and Nucleoside Peptides as Inhibitors. Pestic Biochem Physiol. 37(3):249–253. doi:10.1016/0048-3575(90)90131-K.

Kuwano E, Cohen E. 1984. The use of a Tribolium chitin synthetase assay in studying the effects of benzimidazoles with a terpene moiety and related compounds. Agric Biol Chem. 48(6):1617–1620. doi:10.1080/00021369.1984.10866362.

Latgé JP. 2007. The cell wall: A carbohydrate armour for the fungal cell. Mol Microbiol. 66(2):279–290. doi:10.1111/j.1365-2958.2007.05872.x.

Lucero HA, Kuranda MJ, Bulik DA. 2002. A nonradioactive, high throughput assay for chitin synthase activity. Anal Biochem. 305(1):97–105. doi:10.1006/abio.2002.5594.

Lukens RJ, Sisler HD. 1958. 2-Thiazolidinethione-4-carboxylic acid from the reaction of captan with cysteine. Science (80- ). 127(3299):650. doi:10.1126/science.127.3299.650.

Merzendorfer H. 2006. Insect chitin synthases: A review. J Comp Physiol B Biochem Syst Environ Physiol. doi:10.1007/s00360-005-0005-3.

Merzendorfer H. 2011. The cellular basis of chitin synthesis in fungi and insects: Common principles and differences. Eur J Cell Biol. 90(9):759–769. doi:10.1016/j.ejcb.2011.04.014. http://dx.doi.org/10.1016/j.ejcb.2011.04.014.

Merzendorfer H, Zimoch L. 2003. Chitin metabolism in insects: structure, function and regulation of chitin synthases and chitinases. J Exp Biol. 206(24):4393 LP – 4412. doi:10.1242/jeb.00709. http://jeb.biologists.org/content/206/24/4393.abstract.

Osada H. 2019. Discovery and applications of nucleoside antibiotics beyond polyoxin. J Antibiot (Tokyo). 72(12):855–864. doi:10.1038/s41429-019-0237-1. http://dx.doi.org/10.1038/s41429-019-0237-1.

Zhang X, Yan Zhu K. 2013. Biochemical characterization of chitin synthase activity and inhibition in the African malaria mosquito, Anopheles gambiae. Insect Sci. 20(2):158–166. doi:10.1111/j.1744-7917.2012.01568.x.

Zhang X, Zhang J, Park Y, Zhu KY. 2012. Identification and characterization of two chitin synthase genes in African malaria mosquito, Anopheles gambiae. Insect Biochem Mol Biol. 42(9):674–682. doi:10.1016/j.ibmb.2012.05.005. http://dx.doi.org/10.1016/j.ibmb.2012.05.005.