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首页> 外文期刊>Biochemistry >Spontaneous, pH-dependent membrane insertion of a transbilayer alpha-helix
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Spontaneous, pH-dependent membrane insertion of a transbilayer alpha-helix

机译：自发的，pH依赖性的跨双层α-螺旋膜插入

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A question of fundamental importance concerning the biosynthesis of integral membrane proteins is whether transmembrane secondary structure can insert spontaneously into a lipid bilayer. It has proven to be difficult to address this issue experimentally because of the poor solubility in aqueous solution of peptides and proteins containing these extremely hydrophobic sequences. We have identified a system in which the kinetics and thermodynamics of alpha-helix insertion into lipid bilayers can be studied systematically and quantitatively using simple spectroscopic assays. Specifically, we have discovered that a 36-residue polypeptide containing the sequence of the C-helix of the integral membrane protein bacteriorhodopsin exhibits significant solubility in aqueous buffers free of both detergents and denaturants. This helix contains two aspartic acid residues in the membrane-spanning region. At neutral pH, the peptide associates with lipid bilayers in a nonhelical and presumably peripheral conformation. With a pKa of 6.0, the peptide inserts into the bilayer as a transbilayer alpha-helix. The insertion reaction proceeds rapidly at room temperature and is fully reversible.
机译：关于完整膜蛋白的生物合成的根本重要性的问题是跨膜二级结构是否可以自发插入脂质双层。由于含有这些极疏水序列的肽和蛋白质在水溶液中的溶解性较差，因此实验证明很难解决这个问题。我们已经确定了一个系统，其中可以使用简单的光谱分析系统地和定量地研究将α-螺旋插入脂质双层的动力学和热力学。具体而言，我们发现包含完整膜蛋白细菌视紫红质的C-螺旋序列的36个残基的多肽在不含去污剂和变性剂的水性缓冲液中表现出显着的溶解性。该螺旋在跨膜区域包含两个天冬氨酸残基。在中性pH下，该肽与脂质双层结合，呈非螺旋状，可能是外围构象。 pKa为6.0时，该肽作为跨双分子α-螺旋插入双层中。插入反应在室温下迅速进行并且是完全可逆的。

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