SP-B and SP-C alter diffusion in bilayers of pulmonary surfactant.
SP-B and SP-C alter diffusion in bilayers of pulmonary surfactant.
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DOI：
10.1529/biophysj.103.037630
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发表时间：
2004-06
影响因子：
3.4
通讯作者：
V. Schram;S. Hall
中科院分区：
文献类型：
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作者：
V. Schram;S. Hall
疏水蛋白SP-B和SP-C以一种未知的机制促进肺表面活性物质在空气/水界面的快速吸附。我们测试了这样的假设，即这些蛋白质通过破坏脂质双层的结构来加速吸附，要么是通过流动性的普遍增加，要么是通过在双层内集中诱导界面边界。我们使用光漂白后的荧光恢复来测量nitrobenzoxadiazolyl-dimyristoyl-phosphatidylethanolamine在11至54℃的多层膜中的扩散，该多层膜包含全套脂肪和小牛肺表面活性物质提取物中的蛋白质，或全套中性和不含蛋白质的磷脂。在35℃以上，CLSE和中性磷脂的Arrhenius扩散图是平行的，但CLSE的扩散图向较低的值移动，这表明蛋白质使脂双层变硬，而不是产生所提出的膜流动性增加。CLSE的Arrhenius曲线的斜率在35摄氏度以下更陡峭，这表明蛋白质在那个温度下诱导相分离。流动部分降至27摄氏度以下，与凝胶和液晶共存的渗流阈值一致。然而，CLSE中侧向相分离的诱导与该温度下吸附动力学的明显变化无关。我们的结果表明，SP-B和SP-C可能通过稳定高能、高弯曲的吸附中间体来促进吸附，而不是通过破坏表面活性剂双层来促进吸附。
The hydrophobic proteins SP-B and SP-C promote rapid adsorption of pulmonary surfactant to an air/water interface by an unknown mechanism. We tested the hypothesis that these proteins accelerate adsorption by disrupting the structure of the lipid bilayer, either by a generalized increase in fluidity or by a focal induction of interfacial boundaries within the bilayer. We used fluorescence recovery after photobleaching to measure diffusion of nitrobenzoxadiazolyl-dimyristoyl-phosphatidylethanolamine between 11 and 54 degrees C in multilayers containing the complete set of lipids and proteins in calf lung surfactant extract (CLSE), or the complete set of neutral and phospholipids without the proteins. Above 35 degrees C, Arrhenius plots of diffusion were parallel for CLSE and neutral and phospholipids, but shifted to lower values for CLSE, suggesting that the proteins rigidify the lipid bilayer rather than producing the proposed increase in membrane fluidity. The slopes of the Arrhenius plots for CLSE were steeper below 35 degrees C, suggesting that the proteins induce phase separation at that temperature. The mobile fraction fell below 27 degrees C, consistent with a percolation threshold of coexisting gel and liquid-crystal phases. The induction of lateral phase separation in CLSE, however, does not correlate with apparent changes in adsorption kinetics at this temperature. Our results suggest that SP-B and SP-C accelerate adsorption through a mechanism other than the disruption of surfactant bilayers, possibly by stabilizing a high-energy, highly curved adsorption intermediate.