Cry proteins become toxic after:
Bt protoxins are inert in plant tissues because solubilization and cleavage conditions absent in neutral pH plant cells. Upon ingestion by susceptible larvae, midgut lumen alkalinity dissociates crystal lattice, releasing soluble protoxin. Midgut serine proteases like trypsin and chymotrypsin cleave N-terminus 28 and C-terminus half, exposing hydrophobic helix alpha-1 for membrane insertion. Resulting 60 to 65 kDa toxin undergoes conformational change induced by cadherin receptor binding, leading to oligomerization into pre-pore tetramer that inserts into apical microvilli causing osmotic imba
Ref: Bravo Biochim Biophys Acta 2007 activation; NCBI NBK24601; Pardo-Lopez Peptides 2013 cleavage; PubMed 16885436.
