NMR structures of the C-terminal segment of surfactant protein B in detergent micelles and hexafluoro-2-propanol
NMR structures of the C-terminal segment of surfactant protein B in detergent micelles and hexafluoro-2-propanol
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DOI：
10.1021/bi0481895
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发表时间：
2004-12-07
期刊：
影响因子：
2.9
通讯作者：
Keough, KMW
中科院分区：
文献类型：
--
作者：
Booth, V;Waring, AJ;Keough, KMW
尽管膜相关表面活性剂蛋白B （SP-B）是肺表面活性剂的重要组成部分，而肺表面活性剂本身对生命至关重要，但其活性的分子基础尚不清楚。SP-B的生物物理功能可以部分地被蛋白质的亚片段模仿，包括c端。我们已经用核磁共振确定了人类SP-B的c端片段的结构，包括残基63-78。对六氟-2-丙醇氟化醇（HFIP）和十二烷基硫酸钠（SDS）胶束进行了结构测定。在两种溶剂中，残基68-78呈现两亲螺旋结构，与同源皂苷家族蛋白的比较预测一致。在HFIP中，肽的五个n端残基在很大程度上是非结构化的，而在SDS胶束中，这些残基具有明确的紧密构象。两种溶剂的螺旋残基侧链定位也存在差异，疏水面结构比亲水性面结构更一致。用顺磁探针研究了该肽在SDS胶束中的位置，结果表明该肽位于水界面，螺旋的疏水性面向内，螺旋的亲水性面向外，n端残基比A -螺旋亲水性面的残基离胶束中心更远。SP-B的碱性残基与阴离子脂质头基团的相互作用已知对功能有影响，这些研究通过观察HFIP和SDS测定的肽结构之间的差异来证明这种相互作用的结构分支。
Although the membrane-associated surfactant protein B (SP-B) is an essential component of lung surfactant, which is itself essential for life, the molecular basis for its activity is not understood. SP-B's biophysical functions can be partially mimicked by subfragments of the protein, including the C-terminus. We have used NMR to determine the structure of a C-terminal fragment of human SP-B that includes residues 63-78. Structure determination was performed both in the fluorinated alcohol hexafluoro-2-propanol (HFIP) and in sodium dodecyl sulfate (SDS) micelles. In both solvents, residues 68-78 take on an amphipathic helical structure, in agreement with predictions made by comparison to homologous saposin family proteins. In HFIP, the five N-terminal residues of the peptide are largely unstructured, while in SDS micelles, these residues take on a well-defined compact conformation. Differences in helical residue side chain positioning between the two solvents were also found, with better agreement between the structures for the hydrophobic face than the hydrophilic face. A paramagnetic probe was used to investigate the position of the peptide within the SDS micelles and indicated that the peptide is located at the water interface with the hydrophobic face of the helix oriented inward, the hydrophilic face of the helix oriented outward, and the N-terminal residues even farther from the micelle center than those on the hydrophilic face of the a-helix. Interactions of basic residues of SP-B with anionic lipid headgroups are known to have an impact on function, and these studies demonstrate structural ramifications of such interactions via the differences observed between the peptide structures determined in HFIP and SDS.