Background Bacillus thuringiensis (Bt) toxin Cry4Ba specifically targets the mosquito larval midgut epithelial cells for its insecticidal toxicity. Prior to reaching the midgut cells, the toxin must penetrate the midgut peritrophic membrane (PM), an acellular gut protective structure lining the midgut epithelium. However, the mechanism of toxin passage through the PM is currently unknown. To ex...

Receptor binding plays an important role in determining host specificity of the Bacillus thuringiensis Cry delta-endotoxins. Mutations in domains II and III have suggested the participation of certain residues in receptor recognition and insect specificity. In the present study, we expressed the cloned domain II-III fragment of Cry4Ba and examined its binding characteristics to mosquito-larval ...

The insecticidal activity of Bacillus thuringiensis (Bt) Cry toxins involves toxin stabilization, oligomerization, passage across the peritrophic membrane (PM), binding to midgut receptors and pore-formation. The residues Arg-158 and Tyr-170 have been shown to be crucial for the toxicity of Bt Cry4Ba. We characterized the biological function of these residues. In mosquito larvae, the mutants R1...

Unicellular micro-alga Chlamydomonas reinhardtii has been recognized as a promising host for expressing recombinant proteins albeit its limited utility due to low levels of heterologous protein expression. Here, transcription of the 3.4-kb mosquito-larvicidal cry4Ba gene from Bacillus thuringiensis in transgenic C. reinhardtii chloroplasts under control of the promoter and 5'-untranslated regio...

Helix 7 in the Cry4Ba-pore-forming domain contains conserved Tyr(249) and Phe(264) that are crucially involved in mosquito-larvicidal activity. We have now characterized lipid-induced conformation of a 27-residue Cry4Ba-alpha7 peptide in phospholipid membranes using ATR-FTIR and hydrogen/deuterium (H(+)/D(+)) exchange experiments. ATR-FTIR results showed that conformation of this peptide is inf...

Mendelian crosses were used to analyze the patterns of inheritance of Cry-toxin resistance in two colonies of Culex quinquefasciatus Say larvae resistant to bacterial toxins produced by Bacillus thuringiensis subsp. israelensis de Barjac. Resistance levels exceeded 1000-fold at 95% lethal concentration of the CryllAa-resistant colony (Cq11A). F1 offspring of reciprocal crosses to a susceptible ...

The insecticidal feature of the three-domain Cry δ-endotoxins from Bacillus thuringiensis is generally attributed to their capability to form oligomeric pores, causing lysis of target larval midgut cells. However, the molecular description of their oligomerization process has not been clearly defined. Here a stable prepore of the 65-kDa trypsin-activated Cry4Ba mosquito-specific toxin was estab...

Mendelian crosses were used to study the mode of inheritance of Cry toxin resistance in a Culex quinquefasciatus Say (Diptera: Culicidae) colony (CqAB11A) that evolved insecticide resistance under laboratory selection with a deletion mutant of Bacillus thuringiensis subsp. israelensis de Barjac lacking the Cyt1Aa toxin component but containing its three major Cry toxins, Cry4Aa, Cry4Ba, and Cry...

Cry4Aa toxin is one of the highly specific mosquito-larvicidal proteins produced by the bacterium Bacillus thuringiensis subspecies israelensis. It is thought to form pores in the larval midgut membrane that cause membrane leakage and subsequent insect death. Therefore, Cry4Aa and other Cry toxins have been used as efficient and safe bacterial insecticides to control the disease-carrying mosqui...

The 65 kDa functional form of the mosquito-larvicidal Cry4Aa-R235Q mutant toxin has been crystallized. The crystals belong to space group C222(1), with unit-cell parameters a = 91.2, b = 202.1, c = 98.7 A, and contain one molecule per asymmetric unit. The crystals diffract to approximately 2.9 A using synchrotron radiation and a complete native data set has been collected. The structure has bee...