Delta endotoxins
| Delta endotoxin, N-terminal domain | |||||||||
|---|---|---|---|---|---|---|---|---|---|
TCDB 1.C.2 | | ||||||||
| |||||||||
| Delta endotoxin, middle domain | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | Endotoxin_M | ||||||||
TCDB | 1.C.2 | ||||||||
| |||||||||
| Delta endotoxin, middle domain, Cry2A and Cry18 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| |||||||||
| Delta endotoxin, C-terminal | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | Endotoxin_C | ||||||||
TCDB | 1.C.2 | ||||||||
| CDD | cd04085 | ||||||||
| |||||||||
| Cytolytic delta-endotoxin Cyt1/2 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | CytB | ||||||||
TCDB | 1.C.71 | ||||||||
| |||||||||
Delta endotoxins (δ-endotoxins) are a family of
Mechanism of action
When an insect ingests these proteins, they are activated by proteolytic cleavage. The N-terminus is cleaved in all of the proteins and a C-terminal extension is cleaved in some members. Once activated, the endotoxin binds to the gut
For many years there was no clarity as to the relationship between
Structure
The activated region of the delta toxin is composed of three distinct
Types
B. thuringiensis encodes many proteins of the delta endotoxin family (InterPro: IPR038979), with some strains encoding multiple types simultaneously.[9] A gene mostly found on plasmids,[10] delta-entotoxins sometimes show up in genomes of other species, albeit at a lower proportion than those found in B. thuringiensis.[11] The gene names looks like Cry3Bb, which in this case indicates a Cry toxin of superfamily 3 family B subfamily b.[12]
Cry proteins that are interesting to cancer research are listed under a parasporin (PS) nomenclature in addition to the Cry nomenclature. They do not kill insects, but instead kill leukemia cells.[13][14][15] The Cyt toxins tend to form their own group distinct from Cry toxins.[16] Not all Cry — crystal-form — toxins directly share a common root.[17] Examples of non-three-domain toxins that nevertheless have a Cry name include Cry34/35Ab1 and related beta-sandwich binary (Bin-like) toxins, Cry6Aa, and many beta-sandwich parasporins.[18]
Specific delta-endotoxins that have been inserted with
Some insects populations have started to develop resistance towards delta endotoxin, with five resistant species found as of 2013. Plants with two kinds of delta endotoxins tend to make resistance happen slower, as the insects have to evolve to overcome both toxins at once. Planting non-Bt plants with the resistant plants will reduce the selection pressure for developing the toxin. Finally, two-toxin plants should not be planted with one-toxin plants, as one-toxin plants act as a stepping stone for adaption in this case.[19]
References
- ^ PMID 11468393.
- ^ Roger Hull; et al. (2021). "Risk assessment and management—Environment". Genetically Modified Plants (second ed.).
Upon sporulation, B. thuringiensis forms proteinaceous insecticidal δ-endotoxins either in crystals (Cry toxins) or cytoplasmically (Cyt toxins), which are encoded by cry or cyt genes, respectively. When insects ingest toxin crystals, the enzymes in their digestive tract cause the toxin to become activated. The toxin binds to the insect's gut membranes, forming a pore that results in swelling, cell lysis, and eventually killing the insect. B. thuringiensis also produces insecticidal proteins at other stages in its lifecycle, specifically the vegetative insecticidal proteins (VIPs)
- ^ PMID 7490762.
- ^ PMID 11729083.
- S2CID 5928827.
- S2CID 13982571.
- ^ PMID 22540421.
- ^ PMID 22617276.
- ^ "Pesticidal crystal protein (IPR038979)". InterPro. Retrieved 12 April 2019.
- PMID 6443645.
- ^ "Species: Pesticidal crystal protein (IPR038979)". InterPro.
- ^ "Bacillus thuringiensis Toxin Nomenclature". Bt toxin specificity database. Retrieved 12 April 2019.
- PMID 10882663.
- PMID 19331182.
- ^ "List of Parasporins". Committee of Parasporin Classification and Nomenclature. Accessed Jan 4, 2013
- ^ Crickmore N. "Other Cry Sequences" (PDF). Retrieved 12 April 2019.
- PMID 9729610.
- PMID 25390338.
- ^ S2CID 205278530.
- PMID 20415781.
Further reading
- Bravo A, Gill SS, Soberón M (March 2007). "Mode of action of Bacillus thuringiensis Cry and Cyt toxins and their potential for insect control". Toxicon. 49 (4): 423–435. PMID 17198720.
- Pigott CR, Ellar DJ (June 2007). "Role of receptors in Bacillus thuringiensis crystal toxin activity". Microbiology and Molecular Biology Reviews. 71 (2): 255–281. PMID 17554045.
- Palma L, Muñoz D, Berry C, Murillo J, Caballero P (December 2014). "Bacillus thuringiensis toxins: an overview of their biocidal activity". Toxins. 6 (12): 3296–3325. PMID 25514092.