Cry proteins are pore forming toxins that, after their solubilization and activation in the insect midgut, bind to specific receptors in the microvilli of midgut epithelial cells.
Then, they bind to specific receptors of the midgut cells (Cry toxins), or directly interact with the cell membrane (Cyt1A toxin), ultimately causing pore formation and cell lysis [ 16].
In susceptible larvae, the toxic crystal is dissolved in the alkaline pH of the midgut, protoxins are then activated by digestive proteases to activated-toxins that bind to specific membrane receptors, form pores, disrupt the midgut epithelium, allowing spore penetration and bacterial proliferation in the host tissues [ 7, 8].
The recent demonstration that Cry2A toxins bind to specific sites located in the brush border of the midgut of H. armigera [8], [9] and H. zea [9] also showed that these sites were different from those of Cry1A proteins.
The toxic action of Bt in vivo is known to be dependent on the binding of activated toxin to the external surface of midgut microvilli, where the toxins appear to bind to specific proteins receptors [ 36, 37] and then intercalate forming transmembrane cation pores [ 38] that lead to cell death.
The activated Cry toxins bind to specific protein receptors, insert into the membrane and form pores, resulting in midgut disruption, bacterial infection and death of the insect.
These proteins bind to specific sites on DNA and (for example) turn on expression of specific genes.
