A polyalanine-based peptide cannot form a stable transmembrane alpha-helix in fully hydrated phospholipid bilayers.
A polyalanine-based peptide cannot form a stable transmembrane alpha-helix in fully hydrated phospholipid bilayers.
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基于聚丙氨酸的肽不能在完全水合的磷脂双层中形成稳定的跨膜α螺旋。
DOI：
10.1021/bi010555m
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发表时间：
2001
期刊：
影响因子：
2.9
通讯作者：
McElhaney,RN
中科院分区：
文献类型：
--
作者：
Lewis,RN;Zhang,YP;Hodges,RS;Subczynski,WK;Kusumi,A;Flach,CR;Mendelsohn,R;McElhaney,RN
用多种物理方法研究了乙酰基-K2-A24-K2-酰胺(A24)的构象、酰胺质子交换性能及其与磷脂酰胆碱双层膜的相互作用。当溶解在甲醇中或从甲醇中浇铸成干膜时，A24主要是α螺旋的。然而，在水介质中，A24主要以螺旋(尽管不一定是α-螺旋)和随机卷曲结构的混合物存在，这两种结构都允许所有酰胺质子的快速H−D交换。当在没有水的情况下结合到磷脂中时，A24也主要以跨膜α-螺旋的形式存在。然而，当该体系水合时，所有的酰胺质子也发生快速交换，同时多肽的酰胺I吸收带也发生了显著变化。此外，当与磷脂酰胆碱分散在水介质中时，A24的构象和热稳定性不会因磷脂的存在或其凝胶/液晶相变而显著改变。差示扫描量热法和电子自旋共振谱研究表明，A24对脂族碳氢链-熔融相变的热力学性质影响较小，不会取消脂族碳氢链的预跃迁，对磷脂族碳氢链的取向顺序或运动速率也没有显著影响。因此，我们得出结论，A24有足够的α-螺旋倾向，但疏水性不足，在水存在的情况下与磷脂双层保持稳定的跨膜结合。相反，它主要以螺旋和其他构象的动态混合物存在，主要存在于与双层表面或与磷脂酰胆碱双层的极性/非极性界面区域弱相互作用的水相中。因此，基于聚丙氨酸的多肽不是天然膜蛋白跨膜α-螺旋片段的良好模型。
The conformation and amide proton exchangeability of the peptide acetyl-K2-A24-K2-amide (A24) and its interaction with phosphatidylcholine bilayers were examined by a variety of physical techniques. When dissolved in or cast from methanol as a dried film, A24is predominantly α-helical. In aqueous media, however, A24exists primarily as a mixture of helical (though not necessarily α-helical) and random coiled structures, both of which allow rapid H−D exchange of all amide protons. When incorporated into phospholipids in the absence of water, A24also exists primarily as a transmembrane α-helix. However, upon hydration of that system, rapid exchange of all amide protons also occurs along with a marked change in the amide I absorption band of the peptide. Also, when dispersed with phosphatidylcholine in aqueous media, the conformation and thermal stability of A24are not significantly altered by the presence of the phospholipid or by its gel/liquid-crystalline phase transition. Differential scanning calorimetric and electron spin resonance spectroscopic studies indicate that A24has relatively minor effects on the thermodynamic properties of the lipid hydrocarbon chain-melting phase transition, that it does not abolish the lipid pretransition, and that its presence has no significant effect on the orientational order or rates of motion of the phospholipid hydrocarbon chains. We therefore conclude that A24has sufficient α-helical propensity, but insufficient hydrophobicity, to maintain a stable transmembrane association with phospholipid bilayers in the presence of water. Instead, it exists primarily as a dynamic mixture of helices and other conformers and resides mostly in the aqueous phase where it interacts weakly with the bilayer surface or with the polar/apolar interfacial region of phosphatidylcholine bilayers. Thus, polyalanine-based peptides are not good models for the transmembrane α-helical segments of natural membrane proteins.