Abstract
Bacillus thuringiensis (Bt) is a ubiquitous bacterium in soils, insect cadavers, phylloplane, water, and stored grain, that produces several proteins, each one toxic to different biological targets such as insects, nematodes, mites, protozoa, and mammalian cells. Most Bt toxins identify their particular target through the recognition of specific cell membrane receptors. Cry proteins are the best-known toxins from Bt and a great amount of research has been published. Cry are cytotoxic to insect larvae that affect important crops recognizing specific cell membrane receptors such as cadherin, aminopeptidase-N, and alkaline phosphatase. Furthermore, some Cry toxins such as Cry4A, Cry4B, and Cry11A act synergistically with Cyt toxins against dipteran larvae vectors of human disease. Research developed with Cry proteins revealed that these toxins also could kill human cancer cells through the interaction with specific receptors. Parasporins are a small group of patented toxins that may or may not have insecticidal activity. These proteins could kill a wide variety of mammalian cancer cells by recognizing specific membrane receptors, just like Cry toxins do. Surface layer proteins (SLP), unlike the other proteins produced by Bt, are also produced by most bacteria and archaebacteria. It was recently demonstrated that SLP produced by Bt could interact with membrane receptors of insect and human cancer cells to kill them. Cyt toxins have a structure that is mostly unrelated to Cry toxins; thereby, other mechanisms of action have been reported to them. These toxins affect mainly mosquitoes that are vectors of human diseases like Anopheles spp (malaria), Aedes spp (dengue, zika, and chikungunya), and Culex spp (Nile fever and Rift Valley fever), respectively. In addition to the Cry, Cyt, and parasporins toxins produced during spore formation as inclusion bodies, Bt strains also produce Vip (Vegetative insecticidal toxins) and Sip (Secreted insecticidal proteins) toxins with insecticidal activity during their vegetative growth phase.
Highlights
BacillusGram-positive and widely distributed distributed in Bacillus thuringiensis thuringiensis is is aa Gram-positive and sporulated sporulated bacterium bacterium that that is is widely in soils, plants, and insects around the world [1,2].Bt is well known because it produces a great variety soils, plants, and insects around the world [1,2]
The binding between Cry toxin and cadherin receptor the activation of adenylyl cyclase; which triggers an increase in cAMP and activates protein kinase induces the activation of adenylyl cyclase; which triggers an increase in cAMP and activates protein kinase A (PKA)
These proteins act in a similar way to Cry toxins because they are highly specific to a cell type, it is well known that Cry toxins specificity depends on cell membrane receptors recognition
Summary
Gram-positive and widely distributed distributed in Bacillus thuringiensis thuringiensis is is aa Gram-positive and sporulated sporulated bacterium bacterium that that is is widely in soils, plants, and insects around the world [1,2]. Bt is well known because it produces a great variety of of useful proteins for pest control in agriculture (Cry, Vip, Sip). [5], inhibits pathogens development in animals and because it induces cytotoxicity in human cancer cells Cry and Cyt delta-endotoxins with 78% sequence identity differ in secondary a capital letter is added to their name, e.g., Cyt1A, Cry1A, Cry2A. Toxins with 95% identity constitute the border for a tertiary rank and small letters differentiate these proteins from each other, e.g., Cyt1Aa, Cry1Aa, Cry1Ab, Cry1Ac [13,14,15]. Parasporins have less than 25% amino acid sequence homology with Cry toxins [7] Their mechanism of action is very similar; both families recognize specific membrane receptors on cancer cells to trigger cell death [6]. Leading Toxic Proteins of Bacillus thuringiensis and their Mechanism of Action
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