In Situ and Real-Time SFG Measurements Revealing Organization and Transport of Cholesterol Analogue 6-Ketocholestanol in a Cell Membrane.
In Situ and Real-Time SFG Measurements Revealing Organization and Transport of Cholesterol Analogue 6-Ketocholestanol in a Cell Membrane.
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DOI：
10.1021/jz402537w
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发表时间：
2014-01
期刊：
影响因子：
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通讯作者：
Sulan Ma;Hongchun Li;Kangzhen Tian;Shuji Ye;Yi Luo
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作者：
Sulan Ma;Hongchun Li;Kangzhen Tian;Shuji Ye;Yi Luo
胆固醇在细胞膜内的组织和运输对人类健康至关重要，到目前为止，许多细胞功能仍然难以捉摸。以胆固醇类似物6-酮基胆甾醇(6-KC)为模型，通过结合非手性敏感的SSP(PPP)和手性敏感的PSP极化测量，我们成功地利用和频产生振动光谱(SFG-VS)来跟踪胆固醇在膜中的组织和运输。结果表明，6-KC分子以10°左右的倾角排列在DMPC脂双层的外层小叶上。6-KC在低6-KC浓度下形成α-β结构，在高6-KC浓度下最有可能形成β-β结构。在所有已提出的模型中，我们的结果支持形成6-KC团簇的所谓伞形模型。此外，我们还发现，期待已久的6-KC在膜中的翻转运动需要时间，至少比之前认为的要长得多。所有这些有趣的发现表明，探索原位、实时和无标记的方法来获得胆固醇在膜中行为的准确分子描述是至关重要的。本研究是首次应用SFG在分子水平上揭示胆固醇-脂质相互作用机制。
Cholesterol organization and transport within a cell membrane are essential for human health and many cellular functions yet remain elusive so far. Using cholesterol analogue 6-ketocholestanol (6-KC) as a model, we have successfully exploited sum frequency generation vibrational spectroscopy (SFG-VS) to track the organization and transport of cholesterol in a membrane by combining achiral-sensitive ssp (ppp) and chiral-sensitive psp polarization measurements. It is found that 6-KC molecules are aligned at the outer leaflet of the DMPC lipid bilayer with a tilt angle of about 10°. 6-KC organizes itself by forming an α-β structure at low 6-KC concentration and most likely a β-β structure at high 6-KC concentration. Among all proposed models, our results favor the so-called umbrella model with formation of a 6-KC cluster. Moreover, we have found that the long anticipated flip-flop motion of 6-KC in the membrane takes time to occur, at least much longer than previously thought. All of these interesting findings indicate that it is critical to explore in situ, real-time, and label-free methodologies to obtain a precise molecular description of cholesterol's behavior in membranes. This study represents the first application of SFG to reveal the cholesterol-lipid interaction mechanism at the molecular level.