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1.  Ser170 of Bacillus thuringiensis Cry1Ab δ-endotoxin becomes anchored in a hydrophobic moiety upon insertion of this protein into Manduca sexta brush border membranes 
BMC Biochemistry  2009;10:25.
Three spin-labeled mutant proteins, mutated at the beginning, middle, and end of α-helix 5 of the Bacillus thuringiensis Cry1Ab δ-endotoxin, were used to study the involvement of these specific amino acid residues in ion transport and to determine conformational changes in the vicinity of these residues when the protein was translocated into a biological membrane.
Amino acid residue leucine 157, located in the N-terminal portion of α-helix 5, showed no involvement in ion transport, and the environment that surrounds the residue did not show any change when transferred into the biological membrane. Serine 170, located in the middle of the α-helix, showed no involvement in ion transport, but our findings indicate that in the membrane-bound state this residue faces an environment that makes the spin less mobile, as opposed to the mobility observed in an aqueous environment. Serine 176, located in the C-terminal end of the α-helix 5 is shown to be involved in ion transport activity.
Ion transport data for L157, S170, and S176, along with the mobility of the spin-labels, structural characterization of the resulting proteins, and toxicity assays against a target insect, suggest that the toxin undergoes conformational changes upon protein translocation into the midgut membrane. These conformational changes result in the midregion of the α-helix 5 being exposed to a hydrophobic-like environment. The location of these three residues in the toxin suggests that the entire α-helix becomes inserted in the insect midgut membrane.
PMCID: PMC2771034  PMID: 19840388
2.  Blocking binding of Bacillus thuringiensis Cry1Aa to Bombyx mori cadherin receptor results in only a minor reduction of toxicity 
BMC Biochemistry  2008;9:3.
Bacillus thuringiensis Cry1Aa insecticidal protein is the most active known B. thuringiensis toxin against the forest insect pest Lymantria dispar (gypsy moth), unfortunately it is also highly toxic against the non-target insect Bombyx mori (silk worm).
Surface exposed hydrophobic residues over domains II and III were targeted for site-directed mutagenesis. Substitution of a phenylalanine residue (F328) by alanine reduced binding to the Bombyx mori cadherin by 23-fold, reduced biological activity against B. mori by 4-fold, while retaining activity against Lymantria dispar.
The results identify a novel receptor-binding epitope and demonstrate that virtual elimination of binding to cadherin BR-175 does not completely remove toxicity in the case of B. mori.
PMCID: PMC2245940  PMID: 18218126
3.  Identification of a Bacillus thuringiensis Cry11Ba toxin-binding aminopeptidase from the mosquito, Anopheles quadrimaculatus 
BMC Biochemistry  2006;7:16.
Aminopeptidase N (APN) type proteins isolated from several species of lepidopteran insects have been implicated as Bacillus thuringiensis (Bt) toxin-binding proteins (receptors) for Cry toxins. We examined brush border membrane vesicle (BBMV) proteins from the mosquito Anopheles quadrimaculatus to determine if APNs from this organism would bind mosquitocidal Cry toxins that are active to it.
A 100-kDa protein with APN activity (APNAnq 100) was isolated from the brush border membrane of Anopheles quadrimaculatus. Native state binding analysis by surface plasmon resonance shows that APNAnq 100 forms tight binding to a mosquitocidal Bt toxin, Cry11Ba, but not to Cry2Aa, Cry4Ba or Cry11Aa.
An aminopeptidase from Anopheles quadrimaculatus mosquitoes is a specific binding protein for Bacillus thuringiensis Cry11Ba.
PMCID: PMC1533836  PMID: 16716213
4.  Binding specificity of Bacillus thuringiensis Cry1Aa for purified, native Bombyx mori aminopeptidase N and cadherin-like receptors 
BMC Biochemistry  2001;2:12.
To better understand the molecular interactions of Bt toxins with non-target insects, we have examined the real-time binding specificity and affinity of Cry1 toxins to native silkworm (Bombyx mori) midgut receptors. Previous studies on B. mori receptors utilized brush border membrane vesicles or purifed receptors in blot-type assays.
The Bombyx mori (silkworm) aminopeptidase N (APN) and cadherin-like receptors for Bacillus thuringiensis insecticidal Cry1Aa toxin were purified and their real-time binding affinities for Cry toxins were examined by surface plasmon resonance. Cry1Ab and Cry1Ac toxins did not bind to the immobilized native receptors, correlating with their low toxicities. Cry1Aa displayed moderate affinity for B. mori APN (75 nM), and unusually tight binding to the cadherin-like receptor (2.6 nM), which results from slow dissociation rates. The binding of a hybrid toxin (Aa/Aa/Ac) was identical to Cry1Aa.
These results indicate domain II of Cry1Aa is essential for binding to native B. mori receptors and for toxicity. Moreover, the high-affinity binding of Cry1Aa to native cadherin-like receptor emphasizes the importance of this receptor class for Bt toxin research.
PMCID: PMC60004  PMID: 11722800

Results 1-4 (4)