1w99
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(New page: 200px<br /><applet load="1w99" size="450" color="white" frame="true" align="right" spinBox="true" caption="1w99, resolution 1.75Å" /> '''MOSQUITO-LARVICIDAL ...)
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Revision as of 03:09, 21 November 2007
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MOSQUITO-LARVICIDAL TOXIN CRY4BA FROM BACILLUS THURINGIENSIS SSP. ISRAELENSIS
Overview
Cry4Ba, isolated from Bacillus thuringiensis subsp. israelensis, is, specifically toxic to the larvae of Aedes and Anopheles mosquitoes. The, structure of activated Cry4Ba toxin has been determined by multiple, isomorphous replacement with anomalous scattering and refined to R(cryst), = 20.5% and R(free)= 21.8% at 1.75 Angstroms resolution. It resembles, previously reported Cry toxin structures but shows the following, distinctions. In domain I the helix bundle contains only the long and, amphipathic helices alpha3-alpha7. The N-terminal helices alpha1-alpha2b, absent due to proteolysis during crystallisation, appear inessential to, toxicity. In domain II the beta-sheet prism presents short apical loops, without the beta-ribbon extension of inner strands, thus placing the, receptor combining sites close to the sheets. In domain III the, beta-sandwich contains a helical extension from the C-terminal strand, beta23, which interacts with a beta-hairpin excursion from the edge of the, outer sheet. The structure provides a rational explanation of recent, mutagenesis and biophysical data on this toxin. Furthermore, added to, earlier structures from the Cry toxin family, Cry4Ba completes a minimal, structural database covering the Coleoptera, Lepidoptera, Diptera and, Lepidoptera/Diptera specificity classes. A multiple structure alignment, found that the Diptera-specific Cry4Ba is structurally more closely, similar to the Lepidoptera-specific Cry1Aa than the Coleoptera-specific, Cry3Aa, but most distantly related to Lepidoptera/Diptera-specific Cry2Aa., The structures are most divergent in domain II, supporting the suggestion, that this domain has a major role in specificity determination. They are, most similar in the alpha3-alpha7 major fragment of domain I, which, contains the alpha4-alpha5 hairpin crucial to pore formation. The, collective knowledge of Cry toxin structure and mutagenesis data will lead, to a more critical understanding of the structural basis for receptor, binding and pore formation, as well as allowing the scope of diversity to, be better appreciated.
About this Structure
1W99 is a Single protein structure of sequence from Bacillus thuringiensis serovar israelensis with BR and P6G as ligands. Full crystallographic information is available from OCA.
Reference
Crystal structure of the mosquito-larvicidal toxin Cry4Ba and its biological implications., Boonserm P, Davis P, Ellar DJ, Li J, J Mol Biol. 2005 Apr 29;348(2):363-82. PMID:15811374
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