Insecticidal delta-endotoxin Cyt2Ba from Bacillus thuringiensis
From Proteopedia
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The crystal structure of the proteolytically activated, monomeric form of Cyt2Ba was solved to 1.8Å resolution. It is composed of a single domain of <scene name='Cyt2Ba/Alpha_beta/1'>α/β</scene> architecture with a β-sheet surrounded by two α-helical layers representing a cytolysin fold. The sheet consists of six anti-parallel β-strands (β1-β6) flanked by an α-helix layer composed of α1, α2 on one side, and by a second α-helix layer composed of α3-α5 on the other. The four longest β-strands (β2-β5) of the central β-sheet have a modified Greek-key topology. | The crystal structure of the proteolytically activated, monomeric form of Cyt2Ba was solved to 1.8Å resolution. It is composed of a single domain of <scene name='Cyt2Ba/Alpha_beta/1'>α/β</scene> architecture with a β-sheet surrounded by two α-helical layers representing a cytolysin fold. The sheet consists of six anti-parallel β-strands (β1-β6) flanked by an α-helix layer composed of α1, α2 on one side, and by a second α-helix layer composed of α3-α5 on the other. The four longest β-strands (β2-β5) of the central β-sheet have a modified Greek-key topology. | ||
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| + | '''Comparison of Cyt2Ba with Structurally Related Proteins''' | ||
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A striking similarity is observed between the structures of the endogenously cleaved Cyt2Ba monomer and the corresponding region within the inactive protoxin dimer of Cyt2Aa. Each monomer of Cyt2Aa, consists of an extra -strand at its N-terminus and -helix at its C-terminus compared to the cleaved <scene name='Cyt2Ba/Alignment_cyt2a/3'>Cyt2Ba</scene>. The dimer interface of Cyt2Aa is held together by the intertwined N-terminal strands from both monomers. The cleavage of Cyt2Aa removes the N and C termini segments, thereby preventing dimer formation and hence releasing a monomer active toxin. Similarly, we show that in Cyt2Ba the proteolysis causes the removal of 34 amino acids at its N-terminal and 28 or 30 residues at its C-terminus forming the crystallized toxic monomer. | A striking similarity is observed between the structures of the endogenously cleaved Cyt2Ba monomer and the corresponding region within the inactive protoxin dimer of Cyt2Aa. Each monomer of Cyt2Aa, consists of an extra -strand at its N-terminus and -helix at its C-terminus compared to the cleaved <scene name='Cyt2Ba/Alignment_cyt2a/3'>Cyt2Ba</scene>. The dimer interface of Cyt2Aa is held together by the intertwined N-terminal strands from both monomers. The cleavage of Cyt2Aa removes the N and C termini segments, thereby preventing dimer formation and hence releasing a monomer active toxin. Similarly, we show that in Cyt2Ba the proteolysis causes the removal of 34 amino acids at its N-terminal and 28 or 30 residues at its C-terminus forming the crystallized toxic monomer. | ||
Revision as of 11:33, 18 May 2008
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| Cyt2Ba, resolution 1.8Å | |||||||
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| Gene: | cyt2Ba | ||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||
The Cyt family of proteins consists of delta-endotoxins expressed during sporulation of several subspecies of Bacillus thuringiensis. Its members possess insecticidal, hemolytic and cytolytic activities through pore formation, and attract attention due to their potential use as vehicles for targeted membrane-destruction. The delta-endotoxin of subsp. israelensis includes three Cyt species, a major Cyt1Aa and two minor proteins Cyt2Ba and Cyt1Ca. Cleaved Cyt protein that lacks the N- and C-terminal segments form toxic monomers. The crystal structure of Cyt2Ba, cleaved at its amino and carboxy terminus by bacterial endogenous protease(s) is presented. Overall, its fold resembles that of the previously described and the non-toxic form of .
The structural similarity between these three proteins may provide information regarding the mechanism(s) of membrane perforating toxins.
The Overall Structure of Monomeric Cyt2Ba
The crystal structure of the proteolytically activated, monomeric form of Cyt2Ba was solved to 1.8Å resolution. It is composed of a single domain of architecture with a β-sheet surrounded by two α-helical layers representing a cytolysin fold. The sheet consists of six anti-parallel β-strands (β1-β6) flanked by an α-helix layer composed of α1, α2 on one side, and by a second α-helix layer composed of α3-α5 on the other. The four longest β-strands (β2-β5) of the central β-sheet have a modified Greek-key topology.
Comparison of Cyt2Ba with Structurally Related Proteins
A striking similarity is observed between the structures of the endogenously cleaved Cyt2Ba monomer and the corresponding region within the inactive protoxin dimer of Cyt2Aa. Each monomer of Cyt2Aa, consists of an extra -strand at its N-terminus and -helix at its C-terminus compared to the cleaved . The dimer interface of Cyt2Aa is held together by the intertwined N-terminal strands from both monomers. The cleavage of Cyt2Aa removes the N and C termini segments, thereby preventing dimer formation and hence releasing a monomer active toxin. Similarly, we show that in Cyt2Ba the proteolysis causes the removal of 34 amino acids at its N-terminal and 28 or 30 residues at its C-terminus forming the crystallized toxic monomer.
Cyt2Ba monomer (lavender) and Cyt2Aa dimer (monomer A - red and monomer B - blue) (PDB accession code 1cby) are shown. Note, the N-terminal intertwined strands and the C-terminal helices of Cyt2Aa are involved in dimer formation. Both segments do not exist in the proteolytically cleaved Cyt2Ba structure.
Proteopedia Page Contributors and Editors (what is this?)
Alexander Berchansky, Joel L. Sussman, Eran Hodis, Jaime Prilusky, Michal Harel, David Canner, Eric Martz
