title: Domains II and III of Bacillus thuringiensis Cry1Ab toxin remain exposed to the solvent after insertion of part of domain I into the membrane.
abstract: Bacillus thuringiensis produces insecticidal proteins named Cry toxins, that are used commercially for the control of economical important insect pests. These are pore-forming toxins that interact with different receptors in the insect gut, forming pores in the apical membrane causing cell burst and insect death. Elucidation of the structure of the membrane-inserted toxin is important to fully understand its mechanism of action. One hypothesis proposed that the hairpin of α-helices 4-5 of domain I inserts into the phospholipid bilayer, whereas the rest of helices of domain I are spread on the membrane surface in an umbrella-like conformation. However, a second hypothesis proposed that the three domains of the Cry toxin insert into the bilayer without major conformational changes. In this work we constructed single Cys Cry1Ab mutants that remain active against Manduca sexta larvae and labeled them with different fluorescent probes that have different responses to solvent polarity. Different soluble quenchers as well as a membrane-bound quencher were used to compare the properties of the soluble and brush border membrane-inserted forms of Cry1Ab toxin. The fluorescence and quenching analysis presented here, revealed that domains II and III of the toxin remain in the surface of the membrane and only a discrete region of domain I is inserted into the lipid bilayer, supporting the umbrella model of toxin insertion.
authors.affiliation: Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca 62250, Morelos, Mexico.
authors.forename: Luis Enrique
authors.initials: LE
authors.lastname: Zavala
authors.forename: Liliana
authors.initials: L
authors.lastname: Pardo-López
authors.forename: Pablo Emiliano
authors.initials: PE
authors.lastname: Cantón
authors.forename: Isabel
authors.initials: I
authors.lastname: Gómez
authors.forename: Mario
authors.initials: M
authors.lastname: Soberón
authors.forename: Alejandra
authors.initials: A
authors.lastname: Bravo
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004731:Endotoxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007814:Larva / Q000382:microbiology; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D018402:Manduca / Q000382:microbiology; D008956:Models, Chemical; D010743:Phospholipids / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D010743:Phospholipids; C030956:insecticidal crystal protein, Bacillus Thuringiensis