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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Structure and Conformation of Bipolar Tetraether Lipid Membranes Derived from Thermoacidophilic Archaeon Sulfolobus acidocaldarius as Revealed by Small-Angle X-ray Scattering and High-Pressure FT-IR Spectroscopy
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Structure and Conformation of Bipolar Tetraether Lipid Membranes Derived from Thermoacidophilic Archaeon Sulfolobus acidocaldarius as Revealed by Small-Angle X-ray Scattering and High-Pressure FT-IR Spectroscopy

机译：小角X射线散射和高压FT-IR光谱揭示了嗜热古细菌Sulfolobus acidocaldarius的双极性四醚脂质膜的结构和构型

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The phase behavior, conformation, and structure of bipolar tetraether liposomes composed of the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius have been studied by small-angle X-ray scattering (SAXS) and high-pressure Fourier transform infrared spectroscopy (FT-IR) at pD 2.15. The SAXS data on PLFE multilamellar vesicles in 85 wt % D_2O showed two orders of lamellar Bragg reflections over the temperature range 5-75 ℃. The lamellar repeat distances d indicate three lamellar regions: 5-50 ℃ (d, ～49-50 A), 50-60 ℃(～50-54 A), and 60-74 ℃(～54-56 A). The 4-A increase in d-spacing from 50 to 60 ℃ is probably due to an increase in hydration at the PLFE polar headgroups and/or a stretch of the polar headgroups toward the bulk aqueous phase. At 74-75 ℃, a lamellar-to-cubic phase transition occurs. The reciprocal spacings of the cubic phases correspond to the coexistence of the inverse bicontinuous cubic phases Q_(II)~D and Q_(II)~P with lattice constants of 105 and 82 A, respectively. At atmospheric pressure, the vibrational frequency of the CH_2 symmetric stretching mode showed transitions at ～46-48, 61, and 74 ℃, in agreement with the SAXS data. The overal 2 cm~(-1) increase in wavenumber between 61 and 74 ℃ indicates a transition from a rigid, gellike lipid conformation to a chain conformation with considerable disorder, as expected from cubic phases which appear above ～74 ℃. The pressure dependence (up to 15 kbar) of the symmetric CH_2 stretching vibrational wavenumber at various temperatures has also been examined. A variety of new gellike phases are observed at elevated pressures, showing again a rich polymorphism in PLFE liposomes. The most prominent pressure-induced transition involves a ～2 cm~(-1) increase in wavenumber, which appears at 8.0 kbar at 60 ℃, 8.4 kbar at 43 ℃, and 10.8 kbar at 20 ℃, giving an unusual negative dT/dp value. The possible source of this anomaly has been discussed in terms of the temperature attenuation of the hydrogen bond network in the polar headgroup region.
机译：通过小角度X射线散射（SAXS）和高压傅里叶变换红外光谱研究了由嗜热古细菌Sulfolobus acidocaldarius分离出的极性脂质组分E（PLFE）组成的双极性四醚脂质体的相行为，构象和结构。光谱（FT-IR），pD 2.15。在85 wt％的D_2O中PLFE多层囊泡的SAXS数据在5-75℃的温度范围内表现出2个层状布拉格反射。层状重复距离d表示三个层状区域：5-50℃（d，〜49-50 A），50-60℃（〜50-54 A）和60-74℃（〜54-56 A）。 d间隔从50℃升高到4-A可能是由于PLFE极性头基的水合作用增加和/或极性头基向本体水相的拉伸所致。在74-75℃时，会发生层状到立方的相变。立方相的倒数分别对应于反向双连续立方相Q_（II）〜D和Q_（II）〜P的共存，其晶格常数分别为105和82A。在大气压力下，CH_2对称拉伸模式的振动频率在〜46-48、61和74℃处发生转变，与SAXS数据一致。在61至74℃之间，总波数增加了2 cm〜（-1），表明从刚性的凝胶状脂质构象过渡到具有明显无序的链构象，这是从〜74℃以上出现的立方相所预期的。还研究了在不同温度下对称CH_2拉伸振动波数的压力依赖性（最高15 kbar）。在升高的压力下观察到多种新的凝胶状相，再次显示出PLFE脂质体中丰富的多态性。压力引起的最明显过渡涉及波数增加〜2 cm〜（-1），在60℃时出现8.0 kbar，在43℃时出现8.4 kbar，在20℃时出现10.8 kbar，从而产生异常的dT / dp负值。值。已经根据极性头基区域中氢键网络的温度衰减讨论了这种异常的可能来源。

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