Gazit E, La Rocca P, Sansom M S, Shai Y
Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, 76100, Israel.
Proc Natl Acad Sci U S A. 1998 Oct 13;95(21):12289-94. doi: 10.1073/pnas.95.21.12289.
The aim of this study was to elucidate the mechanism of membrane insertion and the structural organization of pores formed by Bacillus thuringiensis delta-endotoxin. We determined the relative affinities for membranes of peptides corresponding to the seven helices that compose the toxin pore-forming domain, their modes of membrane interaction, their structures within membranes, and their orientations relative to the membrane normal. In addition, we used resonance energy transfer measurements of all possible combinatorial pairs of membrane-bound helices to map the network of interactions between helices in their membrane-bound state. The interaction of the helices with the bilayer membrane was also probed by a Monte Carlo simulation protocol to determine lowest-energy orientations. Our results are consistent with a situation in which helices alpha4 and alpha5 insert into the membrane as a helical hairpin in an antiparallel manner, while the other helices lie on the membrane surface like the ribs of an umbrella (the "umbrella model"). Our results also support the suggestion that alpha7 may serve as a binding sensor to initiate the structural rearrangement of the pore-forming domain.
本研究的目的是阐明苏云金芽孢杆菌δ-内毒素形成的孔的膜插入机制及其结构组织。我们确定了与构成毒素孔形成结构域的七个螺旋相对应的肽对膜的相对亲和力、它们与膜相互作用的模式、它们在膜内的结构以及它们相对于膜法线的方向。此外，我们使用了对膜结合螺旋的所有可能组合对的共振能量转移测量来绘制处于膜结合状态的螺旋之间的相互作用网络。还通过蒙特卡罗模拟协议探测了螺旋与双层膜的相互作用，以确定最低能量取向。我们的结果与以下情况一致：α4和α5螺旋以反平行方式作为螺旋发夹插入膜中，而其他螺旋像伞的肋骨一样位于膜表面（“伞模型”）。我们的结果还支持α7可能作为结合传感器来启动孔形成结构域的结构重排这一观点。
