Insecticidal crystal protein (ICP)

Insecticidal crystal proteins (ICPs), also known as Cry proteins or delta-endotoxins, are a diverse family of pore-forming toxins produced by the gram-positive bacterium Bacillus thuringiensis during its sporulation phase [1][2]. These proteins are widely recognized for their high specificity and toxicity towards various insect orders, including Lepidoptera, Coleoptera, and Diptera, while remaining generally harmless to vertebrates and beneficial insects due to a lack of compatible gut receptors and acidic digestive environments [1][14][15]. ICPs are the primary active ingredients in biopesticides and are the genetic basis for transgenic insect-resistant crops, such as Bt corn and Bt cotton, which have transformed global agricultural pest management [11][13][19]. Beyond their agricultural utility, a specialized subset of these proteins known as parasporins has demonstrated selective cytocidal activity against human cancer cells in vitro, suggesting potential applications as novel anti-cancer therapeutic agents [6][10]. While they are not considered standard therapeutic targets for existing pharmaceuticals, they represent significant subjects of protein engineering to overcome insect resistance and to develop targeted toxins for medical use. The efficacy of ICPs depends heavily on their structural domains, which facilitate receptor recognition, membrane insertion, and pore stabilization, making them a model system for studying pore-forming toxins [12][16].

Other names

Cry proteinDelta-endotoxinBacillus thuringiensis toxinBt toxinParasporal crystal proteinParasporinCrystal toxin

Insecticidal crystal proteins act through a multi-step process beginning with ingestion by a susceptible larva and solubilization in the alkaline environment of the insect midgut. The resulting protoxins are proteolytically activated by midgut proteases into toxic fragments that bind sequentially to specific membrane receptors, such as cadherins, aminopeptidase N, and alkaline phosphatase [1][3][4]. This binding induces the formation of an oligomeric structure that inserts into the apical membrane of the midgut epithelial cells to form pores, leading to osmotic lysis, destruction of the gut epithelium, and eventually the death of the insect [4][5][15].