TY - JOUR
T1 - Cyt1Aa toxin
T2 - Crystal structure reveals implications for its membrane-perforating function
AU - Cohen, Shmuel
AU - Albeck, Shira
AU - Ben-Dov, Eitan
AU - Cahan, Rivka
AU - Firer, Michael
AU - Zaritsky, Arieh
AU - Dym, Orly
N1 - Funding Information:
We thank Prof. Ehud Gazit (Faculty of Life Sciences, Tel-Aviv University) for careful reading of the manuscript and for his constructive comments. We thank Prof. Joel L. Sussman for helpful discussions. The structure of Cyt1Aa was determined at the Israel Structural Proteomics Center. This work was partially supported by grants ( 2001–042 and 2007–037 to A.Z.) from the United States–Israel Binational Science Foundation (Jerusalem, Israel), the Divadol Foundation , the European Commission Sixth Framework Research , and the Technological Development Program (contract no. 031220).
PY - 2011/11/4
Y1 - 2011/11/4
N2 - During sporulation, Bacillus thuringiensis subsp. israelensis produces a mosquito larvicidal protein complex containing several crystalline and cytolytic (Cyt) toxins. Here, the activated monomeric form of Cyt1Aa, the most toxic Cyt family member, was isolated and crystallized, and its structure was determined for the first time at 2.2 Å resolution. Cyt1Aa adopts a typical cytolysin fold containing a β-sheet held by two surrounding α-helical layers. The absence of a β-strand (between residues V26 and I37) in the dimeric structure of Cyt2Aa led us to deduce that this is the only essential segment for dimer formation and that activation of the toxin occurs by proteolytic processing of its N-terminus. Based on the Cyt1Aa structure, we suggest that the toxicity of Cyt1Aa and other nonrelated proteins, all sharing a cytolysin fold, is correlated with their ability to undergo conformational changes that are necessary prior to their membrane insertion and perforation. This fold allows the α-helical layers to swing away, exposing the β-sheet to insert into the membrane. The identification of a putative lipid binding pocket between the β-sheet and the helical layer of Cyt1Aa supports this mechanism. Sequence-based structural analysis of Cyt1Aa revealed that the lack of activity of Cyt1Ca may be related to the latter's inability to undergo this conformational change due to its lack of flexibility. The pattern of the hemolytic activity of Cyt1Aa presented here (resembling that of pore-forming agents), while differing from that imposed by ionic and nonionic detergents, further supports the pore-forming model by which conformational changes occur prior to membrane insertion and perforation.
AB - During sporulation, Bacillus thuringiensis subsp. israelensis produces a mosquito larvicidal protein complex containing several crystalline and cytolytic (Cyt) toxins. Here, the activated monomeric form of Cyt1Aa, the most toxic Cyt family member, was isolated and crystallized, and its structure was determined for the first time at 2.2 Å resolution. Cyt1Aa adopts a typical cytolysin fold containing a β-sheet held by two surrounding α-helical layers. The absence of a β-strand (between residues V26 and I37) in the dimeric structure of Cyt2Aa led us to deduce that this is the only essential segment for dimer formation and that activation of the toxin occurs by proteolytic processing of its N-terminus. Based on the Cyt1Aa structure, we suggest that the toxicity of Cyt1Aa and other nonrelated proteins, all sharing a cytolysin fold, is correlated with their ability to undergo conformational changes that are necessary prior to their membrane insertion and perforation. This fold allows the α-helical layers to swing away, exposing the β-sheet to insert into the membrane. The identification of a putative lipid binding pocket between the β-sheet and the helical layer of Cyt1Aa supports this mechanism. Sequence-based structural analysis of Cyt1Aa revealed that the lack of activity of Cyt1Ca may be related to the latter's inability to undergo this conformational change due to its lack of flexibility. The pattern of the hemolytic activity of Cyt1Aa presented here (resembling that of pore-forming agents), while differing from that imposed by ionic and nonionic detergents, further supports the pore-forming model by which conformational changes occur prior to membrane insertion and perforation.
KW - Bacillus thuringiensis israelensis
KW - Cyt1Ca
KW - Cyt2Aa
KW - Cyt2Ba
KW - VVA2
UR - http://www.scopus.com/inward/record.url?scp=80054847383&partnerID=8YFLogxK
U2 - 10.1016/j.jmb.2011.09.021
DO - 10.1016/j.jmb.2011.09.021
M3 - Article
AN - SCOPUS:80054847383
SN - 0022-2836
VL - 413
SP - 804
EP - 814
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 4
ER -