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1cby
From Proteopedia
| 1cby, resolution 2.60Å () | |||||||||
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| Sites: | and | ||||||||
| Gene: | CYTB (Bacillus thuringiensis) | ||||||||
| Domains: | Bac_thur_toxin | ||||||||
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| Resources: | FirstGlance, OCA, PDBsum, RCSB | ||||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||||
DELTA-ENDOTOXIN
The delta-endotoxin CytB, found in parasporal inclusions of Bacillus thuringiensis subspecies kyushuensis, is a membrane pore-forming protein which is lethal to the larvae of Dipteran insects and broadly cytolytic in vitro. The crystal structure of CytB in the protoxin form has been determined by isomorphous replacement using heavy-atom derivatives of both the wild-type protein and an engineered cysteine mutant. The atomic model comprising residues 19 to 245 and 28 bound water molecules has been refined at 2.6 angstrom resolution to a crystallographic R-factor of 19.7% and a free R-factor of 26.1%. CytB has a single domain of alpha/beta architecture but a novel connectivity comprising two outer layers of alpha-helix hairpins wrapped around a mixed beta-sheet. In the protoxin form, CytB is a dimer linked by the intertwined N-terminal strands in a continuous, 12-stranded beta-sheet. Proteolytic processing cleaves the intertwined beta-strands to release the active CytB as a monomer, as well as removing the C-terminal tail to uncover the three-layered core. The homologous toxin CytA should show the same fold. Mutations in CytA that inhibit expression map to the dimer contacts and to the tip of helix pair A-B in contact with the sheet, apparently preventing correct folding. Mutations that inhibit toxicity map to the edge of the beta-sheet adjoining the helix pair C-D and to the sheet face, while mutations on the helix surfaces have no effect. Therefore segments forming the sheet, rather than the amphiphilic but short helices, are responsible for membrane binding and pore formation. A conformational change is postulated by which the helix pair C-D peels away from the sheet to lie on the membrane surface, while the sheet region rearranges to form an oligomeric trans-membrane pore.
Structure of the mosquitocidal delta-endotoxin CytB from Bacillus thuringiensis sp. kyushuensis and implications for membrane pore formation., Li J, Koni PA, Ellar DJ, J Mol Biol. 1996 Mar 22;257(1):129-52. PMID:8632451
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
Although, 1cby is a 1 chain structure, the biological relevant molecule for 1cby can be assembled from the contents of the deposited coordinates by the application of crystallographic symmetry operations to give a dimer. It can be downloaded. A remarkable similarity is observed between the structures of the endogenously cleaved Cyt2Ba (gray, 2rci) and the (red) within the inactive protoxin of Cyt2Aa (this entry; monomers A and B of Cyt2Aa shown red and blue, respectively, the N- and C-termini are shown in spacefilling representation). Each monomer of Cyt2Aa (1cby), consists of an additional β-strand at its N-terminus and an additional α-helix at its C-terminus compared to the cleaved Cyt2Ba. The of Cyt2Aa is held together by the intertwined N-terminal strands from both monomers. The cleavage of Cyt2Aa the N- and C-terminal segments, prevents dimer formation and releases an . Similarly, in Cyt2Ba the proteolysis causes the removal of 34 amino acids at its N-terminus and 28 or 30 residues at its C-terminus forming the crystallized toxic monomer.
About this Structure
1CBY is a 1 chain structure of sequence from Bacillus thuringiensis. Full crystallographic information is available from OCA.
References
- Li J, Koni PA, Ellar DJ. Structure of the mosquitocidal delta-endotoxin CytB from Bacillus thuringiensis sp. kyushuensis and implications for membrane pore formation. J Mol Biol. 1996 Mar 22;257(1):129-52. PMID:8632451 doi:10.1006/jmbi.1996.0152
- Cohen S, Dym O, Albeck S, Ben-Dov E, Cahan R, Firer M, Zaritsky A. High-resolution crystal structure of activated Cyt2Ba monomer from Bacillus thuringiensis subsp. israelensis. J Mol Biol. 2008 Jul 25;380(5):820-7. Epub 2008 May 11. PMID:18571667 doi:10.1016/j.jmb.2008.05.010
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