title: The Cry4B toxin of Bacillus thuringiensis subsp. israelensis kills Permethrin-resistant Anopheles gambiae, the principal vector of malaria.
abstract: Resurgence of malaria has been attributed, in part, to the development of resistance by Anopheles gambiae, a principal vector of the disease, to various insecticidal compounds such as Permethrin. Permethrin, a neurotoxicant, is widely used to impregnate mosquito nets. An alternative strategy to control mosquitoes is the use of Bacillus thuringiensis subsp. israelensis (Bti) because there is no observable resistance in the field to the bacterium. Bti kills mosquitoes by targeting cadherin molecules residing in the midgut epithelium of larvae of the insect. Cry proteins (Cry4A, Cry4B, Cry10A and Cry11A) produced by the bacterium during the sporulation phase of its life cycle bind to the cadherin molecules, which serve as receptors for the proteins. These Cry proteins have variable specificity to a variety of mosquitoes, including Culex and Aedes as well as Anopheles. Importantly, selective mosquitocidal action is occasioned by binding of the respective Cry toxins to cadherins distinctive to individual mosquito species. Differential fractionation of the four Cry proteins from a novel Bti isolate (M1) and cloning and expression of their genes in Escherichia coli revealed that Cry4B is the only Cry protein that exerts insecticidal action against An. gambiae. Indeed, it does so against a Permethrin-resistant strain of the mosquito. The other three Cry proteins are ineffective. Multiple sequence alignments of the four Cry proteins revealed a divergent sequence motif in the Cry4B toxin, which most likely determines binding of the toxin to its cognate receptor, BT-R3, in An. gambiae and to its specific toxicity. A model showing Cry4B toxin binding to BT-R3 is presented.
authors.affiliation: Department of Molecular and Cell Biology, The University of Texas at Dallas, PO Box 830688, Richardson, TX 75083-0688, USA.
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Ibrahim
authors.forename: Natalya B
authors.initials: NB
authors.lastname: Griko
authors.forename: Lee A
authors.initials: LA
authors.lastname: Bulla
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000472:pathogenicity; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D015820:Cadherins / Q000378:metabolism; D004351:Drug Resistance; D004731:Endotoxins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D041981:Gastrointestinal Tract / Q000378:metabolism; D006460:Hemolysin Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D007303:Insect Vectors / Q000472:pathogenicity*; D007306:Insecticides / Q000494:pharmacology*; D008288:Malaria / Q000209:etiology*; D008969:Molecular Sequence Data; D009032:Mosquito Control; D026023:Permethrin / Q000494:pharmacology*; D011485:Protein Binding; D013045:Species Specificity
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D015820:Cadherins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D026023:Permethrin
keywords: Anopheles gambiae; BT-R3; Bacillus thuringiensis; Cry4B; High Five cells; malaria; mosquito