title: Intermolecular interaction between Cry2Aa and Cyt1Aa and its effect on larvicidal activity against Culex quinquefasciatus.
abstract: The Cyt1Aa protein of Bacillus thuringiensis susbp. israelensis elaborates demonstrable toxicity to mosquito larvae, but more importantly, it enhances the larvicidal activity of this species Cry proteins (Cry11Aa, Cry4Aa, and Cry4Ba) and delays the phenotypic expression of resistance to these that has evolved in Culex quinquefasciatus. It is also known that Cyt1Aa, which is highly lipophilic, synergizes Cry11Aa by functioning as a surrogate membrane-bound receptor for the latter protein. Little is known, however, about whether Cyt1Aa can interact similarly with other Cry proteins not primarily mosquitocidal; for example, Cry2Aa, which is active against lepidopteran larvae, but essentially inactive or has very low toxicity to mosquito larvae. Here we demonstrate by ligand binding and enzyme-linked immunosorbent assays that Cyt1Aa and Cry2Aa form intermolecular complexes in vitro, and in addition show that Cyt1Aa facilitates binding of Cry2Aa throughout the midgut of C. quinquefasciatus larvae. As Cry2Aa and Cry11Aa share structural similarity in domain II, the interaction between Cyt1Aa and Cry2Aa could be a result of a similar mechanism previously proposed for Cry11Aa and Cyt1Aa. Finally, despite the observed interaction between Cry2Aa and Cyt1Aa, only a 2-fold enhancement in toxicity resulted against C. quinquefasciatus. Regardless, our results suggest that Cry2Aa could be a useful component of mosquitocidal endotoxin complements being developed for recombinant strains of B. thuringiensis subsp. israelensis and B. sphaericus aimed at improving the efficacy of commercial products and avoiding resistance.
authors.affiliation: Department of Entomology, University of California, Riverside, Riverside, CA 92521, USA, Department of Natural and Mathematical Sciences, California Baptist University, Riverside, CA 92504, USA.
authors.forename: Dennis K
authors.initials: DK
authors.lastname: Bideshi
authors.forename: Greer
authors.initials: G
authors.lastname: Waldrop
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Fernandez-Luna
authors.forename: Mercedes
authors.initials: M
authors.lastname: Diaz-Mendoza
authors.forename: Margaret C
authors.initials: MC
authors.lastname: Wirth
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Johnson
authors.forename: Hyun-Woo
authors.initials: HW
authors.lastname: Park
authors.forename: Brian A
authors.initials: BA
authors.lastname: Federici
mesh_terms: D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D003465:Culex / Q000187:drug effects*; D004357:Drug Synergism; D004731:Endotoxins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D006460:Hemolysin Proteins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D007814:Larva / Q000187:drug effects; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis