title: The amino- and carboxyl-terminal fragments of the Bacillus thuringensis Cyt1Aa toxin have differential roles in toxin oligomerization and pore formation.
abstract: The Cyt toxins produced by the bacteria Bacillus thuringiensis show insecticidal activity against some insects, mainly dipteran larvae, being able to kill mosquitoes and black flies. However, they also possess a general cytolytic activity in vitro, showing hemolytic activity in red blood cells. These proteins are composed of two outer layers of α-helix hairpins wrapped around a β-sheet. With regard to their mode of action, one model proposed that the two outer layers of α-helix hairpins swing away from the β-sheet, allowing insertion of β-strands into the membrane forming a pore after toxin oligomerization. The other model suggested a detergent-like mechanism of action of the toxin on the surface of the lipid bilayer. In this work, we cloned the N- and C-terminal domains form Cyt1Aa and analyzed their effects on Cyt1Aa toxin action. The N-terminal domain shows a dominant negative phenotype inhibiting the in vitro hemolytic activity of Cyt1Aa in red blood cells and the in vivo insecticidal activity of Cyt1Aa against Aedes aegypti larvae. In addition, the N-terminal region is able to induce aggregation of the Cyt1Aa toxin in solution. Finally, the C-terminal domain composed mainly of β-strands is able to bind to the SUV liposomes, suggesting that this region of the toxin is involved in membrane interaction. Overall, our data indicate that the two isolated domains of Cyt1Aa have different roles in toxin action. The N-terminal region is involved in toxin aggregation, while the C-terminal domain is involved in the interaction of the toxin with the lipid membrane.
authors.affiliation: Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca 62250, Morelos, Mexico.
authors.forename: Claudia
authors.initials: C
authors.lastname: Rodriguez-Almazan
authors.forename: Iñigo
authors.initials: I
authors.lastname: Ruiz de Escudero
authors.forename: Pablo Emiliano
authors.initials: PE
authors.lastname: Cantón
authors.forename: Carlos
authors.initials: C
authors.lastname: Muñoz-Garay
authors.forename: Claudia
authors.initials: C
authors.lastname: Pérez
authors.forename: Sarjeet S
authors.initials: SS
authors.lastname: Gill
authors.forename: Mario
authors.initials: M
authors.lastname: Soberón
authors.forename: Alejandra
authors.initials: A
authors.lastname: Bravo
mesh_terms: D000330:Aedes / Q000187:drug effects; D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry*; D004731:Endotoxins / Q000737:chemistry*; D006460:Hemolysin Proteins / Q000737:chemistry*; D007306:Insecticides / Q000737:chemistry*; D007814:Larva / Q000187:drug effects; D008081:Liposomes / Q000737:chemistry; D008566:Membranes / Q000737:chemistry; D008956:Models, Chemical; D052899:Pore Forming Cytotoxic Proteins / Q000737:chemistry*; D011487:Protein Conformation; D055503:Protein Multimerization
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; D008081:Liposomes; D052899:Pore Forming Cytotoxic Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis