Department of Mechanical Engineering, University of Maryland, College Park, Maryland, United States of America.
PLoS One. 2012;7(9):e43513. doi: 10.1371/journal.pone.0043513. Epub 2012 Sep 12.
Ceramide, a proapoptotic sphingolipid, has been shown to form channels, in mitochondrial outer membranes, large enough to translocate proteins. In phospholipid membranes, electrophysiological studies and electron microscopic visualization both report that these channels form in a range of sizes with a modal value of 10 nm in diameter. A hydrogen bonded barrel-like structure consisting of hundreds of ceramide molecules has been proposed for the structure of the channel and this is supported by electrophysiological studies and molecular dynamic simulations. To our knowledge, the mechanical strength and deformability of such a large diameter but extremely thin cylindrical structure has never been reported. Here we present evidence for a reversible mechanical distortion of the cylinder following the addition of La(3+). A microfluidic system was used to repeatedly lower and then restore the conductance by alternatively perfusing La(3+) and EDTA. Although aspects of the kinetics of conductance drop and recovery are consistent with a disassembly/diffusion/reassembly model, others are inconsistent with the expected time scale of lateral diffusion of disassembled channel fragments in the membrane. The presence of a residual conductance following La(3+) treatment and the relationship between the residual conductance and the initial conductance were both indicative of a distortion/recovery process in analogy with a pressure-induced distortion of a flexible cylinder.
神经酰胺是一种促凋亡的神经鞘脂，已被证明可以在外膜线粒体中形成足够大的通道，以转运蛋白质。在磷脂膜中，电生理研究和电子显微镜可视化都报告说，这些通道的大小在一定范围内，直径的模态值为 10nm。一个由数百个神经酰胺分子组成的氢键桶状结构被提出作为通道的结构，这得到了电生理研究和分子动力学模拟的支持。据我们所知，这种大直径但极薄的圆柱形结构的机械强度和可变形性从未被报道过。在这里，我们提出了在添加 La(3+)后，这种圆柱形结构可发生可逆机械变形的证据。我们使用微流控系统通过交替灌注 La(3+)和 EDTA 来重复降低和恢复电导。虽然电导下降和恢复的动力学的某些方面与组装/扩散/再组装模型一致，但其他方面与膜中组装片段侧向扩散的预期时间尺度不一致。La(3+)处理后存在残余电导，以及残余电导与初始电导之间的关系都表明存在类似于柔性圆柱的压力诱导变形的变形/恢复过程。
