Stability of the two-dimensional lattice of bacteriorhodopsin reconstituted in partially fluorinated phosphatidylcholine bilayers
Stability of the two-dimensional lattice of bacteriorhodopsin reconstituted in partially fluorinated phosphatidylcholine bilayers
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DOI：
10.1016/j.bbamem.2018.12.015
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发表时间：
2019-03-01
影响因子：
3.4
通讯作者：
Sonoyama, Masashi
中科院分区：
文献类型：
--
作者：
Takahashi, Hiroshi;Yoshino, Masaru;Sonoyama, Masashi
本研究旨在研究细菌视紫红质(BR)分子在二(非氟十四烷酰基)磷脂酰胆碱(F4-DMPC)组成的脂双层中的重构，以阐明部分氟化的脂类疏水链对蛋白质稳定性的影响。量热法测量表明，F4-DMPC/BR体系的链熔融转变发生在3.5℃，而可见圆二色谱(CD)和X射线衍射测量表明，在F4-DMPC双层膜中，由BR三聚体形成的二维六方晶格在30℃以上仍保持完好，类似于天然紫膜中的BR。可见CD检测到的三聚体在单体中的完全解离几乎与X射线衍射观察到的2D晶格的完全熔化相吻合，两者都发生在65℃左右(比天然紫膜中的BR低10℃)。在DMPC双层膜中，BR定时器的解离发生在DMPC双层膜的链熔融转变温度附近，而DMPC双层膜中的BR定时器的解离温度约为18℃。为了探索这种稳定性差异背后的原因，我们用简单的电子密度模型分析了片层衍射数据，进一步研究了纯F4-DMPC双层膜的详细结构特征。结果表明，即使发生链熔融转变，全氟烷基团也不会发生构象变化，这可能有助于Br三聚体形成的二维六方晶格的稳定性。
This study aims to investigate bacteriorhodopsin (bR) molecules reconstituted in lipid bilayers composed of di (nonafluorotetradecanoyl)-phosphatidylcholine (F4-DMPC), a partially fluorinated analogue of dimyristoyl-phosphatidylcholine (DMPC) to clarify the effects of partially fluorinated hydrophobic chains of lipids on protein's stability. Calorimetry measurements showed that the chain-melting transition of F4-DMPC/bR systems occurs at 3.5 degrees C, whereas visible circular dichroism (CD) and X-ray diffraction measurements showed that a two-dimensional (2D) hexagonal lattice formed by bR trimers in F4-DMPC bilayers remains intact even above 30 degrees C, similar to bR in a native purple membrane. Complete dissociation of the trimers into the monomers detected by visible CD almost coincides with the complete melting of 2D lattice observed by X-ray diffraction, in which both take place at around 65 degrees C (10 degrees C lower than that for bR in a native purple membrane). However, it is extremely high in comparison with the bR reconstituted in DMPC bilayers in which the dissociation of bR timer in DMPC bilayers occurs near the chain-melting transition temperature of DMPC bilayers at approximately 18 degrees C. In order to explore the rationale behind the difference in stability, a further investigation of the detailed structural features of pure F4-DMPC bilayers was performed by analyzing the lamellar diffraction data using simple electron density models. The results suggested that the perfluoroalkyl groups do not exhibit any conformation change even if the chain-melting transition occurs, which is likely to contribute to the stability of the 2D hexagonal lattice formed by the bR trimers.