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Entropic Anomaly Observed in Lipid Polymorphisms Induced by Surfactant Peptide SP-B(1–25)
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2017-09-25 00:00:00 , DOI: 10.1021/acs.jpcb.7b06538 Nhi Tran 1 , Justin Kurian 2 , Avni Bhatt 2 , Robert McKenna 2 , Joanna R. Long 2
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2017-09-25 00:00:00 , DOI: 10.1021/acs.jpcb.7b06538 Nhi Tran 1 , Justin Kurian 2 , Avni Bhatt 2 , Robert McKenna 2 , Joanna R. Long 2
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The N-terminal 25 amino-acid residues of pulmonary surfactant protein B (SP-B1–25) induces unusual lipid polymorphisms in a model lipid system, 4:1 DPPC/POPG, mirroring the lipid composition of native pulmonary surfactant. It is widely suggested that SP-B1–25-induced lipid polymorphisms within the alveolar aqueous subphase provide a structural platform for rapid lipid adsorption to the air–water interface. Here, we characterize in detail the phase behavior of DPPC and POPG in hydrated lipid assemblies containing therapeutic levels of SP-B1–25 using 2H and 31P solid state NMR spectroscopy. The appearance of a previously observed isotropic lipid phase is found to be highly dependent on the thermal cycling of the samples. Slow heating of frozen samples leads to phase separation of DPPC into a lamellar phase whereas POPG lipids interact with the peptide to form an isotropic phase at physiologic temperature. Rapid heating of frozen samples to room temperature leads to strongly isotropic phase behavior for both DPPC and POPG lipids, with DPPC in exchange between isotropic and interdigitated phases. 31P T2 relaxation times confirm the isotropic phase to be consistent with a lipid cubic phase. The observed phases exhibit thermal stability up to physiologic temperature (37 °C) and are consistent with the formation of a ripple phase containing a large number of peptide-induced membrane structural defects enabling rapid transit of lipids between lipid lamellae. The coexistance of a lipid cubic phase with interdigitated lipids suggests a specific role for the highly conserved N-terminus of SP-B in stabilizing this unusual lipid polymorphism.
中文翻译：
表面活性剂肽SP-B（1–25）诱导的脂质多态性观察到的熵异常。
肺表面活性蛋白B（SP-B 1–25）的N末端25个氨基酸残基在模型脂质系统4：1 DPPC / POPG中诱导了异常的脂质多态性，反映了天然肺表面活性剂的脂质组成。广泛认为，SP-B 1–25诱导的肺泡水亚相中的脂质多态性为脂质快速吸附到空气-水界面提供了结构平台。在这里，我们详细描述了DPPC和POPG在含有治疗水平的SP-B 1–25的水合脂质组装物中的相行为，使用2 H和31P固态NMR光谱。发现先前观察到的各向同性脂质相的外观高度依赖于样品的热循环。冷冻样品的缓慢加热导致DPPC相分离成层状相，而POPG脂质在生理温度下与肽相互作用形成各向同性相。将冷冻样品快速加热至室温会导致DPPC和POPG脂质的强烈各向同性相行为，而DPPC在各向同性相和指间相之间进行交换。31 P Ť 2弛豫时间证实各向同性相与脂质立方相一致。观察到的相表现出直至生理温度（37°C）的热稳定性，并且与包含大量肽诱导的膜结构缺陷的波纹相的形成相一致，从而使脂质能够在脂质层之间快速转移。脂质立方相与指状脂质共存表明，SP-B高度保守的N末端在稳定这种异常的脂质多态性中起特定作用。
更新日期：2017-09-26
中文翻译：
表面活性剂肽SP-B（1–25）诱导的脂质多态性观察到的熵异常。
肺表面活性蛋白B（SP-B 1–25）的N末端25个氨基酸残基在模型脂质系统4：1 DPPC / POPG中诱导了异常的脂质多态性，反映了天然肺表面活性剂的脂质组成。广泛认为，SP-B 1–25诱导的肺泡水亚相中的脂质多态性为脂质快速吸附到空气-水界面提供了结构平台。在这里，我们详细描述了DPPC和POPG在含有治疗水平的SP-B 1–25的水合脂质组装物中的相行为，使用2 H和31P固态NMR光谱。发现先前观察到的各向同性脂质相的外观高度依赖于样品的热循环。冷冻样品的缓慢加热导致DPPC相分离成层状相，而POPG脂质在生理温度下与肽相互作用形成各向同性相。将冷冻样品快速加热至室温会导致DPPC和POPG脂质的强烈各向同性相行为，而DPPC在各向同性相和指间相之间进行交换。31 P Ť 2弛豫时间证实各向同性相与脂质立方相一致。观察到的相表现出直至生理温度（37°C）的热稳定性，并且与包含大量肽诱导的膜结构缺陷的波纹相的形成相一致，从而使脂质能够在脂质层之间快速转移。脂质立方相与指状脂质共存表明，SP-B高度保守的N末端在稳定这种异常的脂质多态性中起特定作用。
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