title: Domain II loop 3 of Bacillus thuringiensis Cry1Ab toxin is involved in a "ping pong" binding mechanism with Manduca sexta aminopeptidase-N and cadherin receptors.
abstract: Bacillus thuringiensis Cry toxins are used worldwide as insecticides in agriculture, in forestry, and in the control of disease transmission vectors. In the lepidopteran Manduca sexta, cadherin (Bt-R(1)) and aminopeptidase-N (APN) function as Cry1A toxin receptors. The interaction with Bt-R(1) promotes cleavage of the amino-terminal end, including helix alpha-1 and formation of prepore oligomer that binds to APN, leading to membrane insertion and pore formation. Loops of domain II of Cry1Ab toxin are involved in receptor interaction. Here we show that Cry1Ab mutants located in domain II loop 3 are affected in binding to both receptors and toxicity against Manduca sexta larvae. Interaction with both receptors depends on the oligomeric state of the toxin. Monomers of loop 3 mutants were affected in binding to APN and to a cadherin fragment corresponding to cadherin repeat 12 but not with a fragment comprising cadherin repeats 7-12. In contrast, the oligomers of loop 3 mutants were affected in binding to both Bt-R(1) fragments but not to APN. Toxicity assays showed that either monomeric or oligomeric structures of Cry1Ab loop 3 mutations were severely affected in insecticidal activity. These data suggest that loop 3 is differentially involved in the binding with both receptor molecules, depending on the oligomeric state of the toxin and also that possibly a "ping pong" binding mechanism with both receptors is involved in toxin action.
authors.affiliation: Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca 62250, Morelos, Mexico.
authors.forename: Sabino
authors.initials: S
authors.lastname: Pacheco
authors.forename: Isabel
authors.initials: I
authors.lastname: Gómez
authors.forename: Ivan
authors.initials: I
authors.lastname: Arenas
authors.forename: Gloria
authors.initials: G
authors.lastname: Saab-Rincon
authors.forename: Claudia
authors.initials: C
authors.lastname: Rodríguez-Almazán
authors.forename: Sarjeet S
authors.initials: SS
authors.lastname: Gill
authors.forename: Alejandra
authors.initials: A
authors.lastname: Bravo
authors.forename: Mario
authors.initials: M
authors.lastname: Soberón
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry*; D018826:CD13 Antigens / Q000737:chemistry*; D015820:Cadherins / Q000737:chemistry*; D002942:Circular Dichroism; D004731:Endotoxins / Q000737:chemistry*; D006460:Hemolysin Proteins / Q000737:chemistry*; D007814:Larva / Q000378:metabolism / Q000382:microbiology; D018402:Manduca / Q000378:metabolism*; D008871:Microvilli / Q000276:immunology; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D015820:Cadherins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D018826:CD13 Antigens