Structure of Apolipoprotein A-I N Terminus on Nascent High Density Lipoproteins
Structure of Apolipoprotein A-I N Terminus on Nascent High Density Lipoproteins
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DOI：
10.1074/jbc.m110.163097
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发表时间：
2011-01-28
影响因子：
4.8
通讯作者：
Oda, Michael N.
中科院分区：
文献类型：
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作者：
Lagerstedt, Jens O.;Cavigiolio, Giorgio;Oda, Michael N.
载脂蛋白A-I（apoA-I）是高密度脂蛋白（HDL）的主要蛋白组分，是胆固醇代谢的关键要素。为了更好地阐明apoA-I结构-功能在胆固醇代谢中的作用，通过电子顺磁共振（EPR）光谱分析来检查新生HDL上的apoA-I N末端（残基6-98）的构象。将在6-98位带有单个氮氧自旋标记的一系列93个apoA-I变体重构到9.6-nm HDL颗粒（rHDL）上。对这些颗粒进行EPR光谱分析，测量区域柔性和侧链溶剂可及性。从侧链移动性和分子可及性阐明二级结构，其中两个主要的α-螺旋结构域定位于残基6-34和50-98。我们鉴定了两个螺旋之间的非结构化片段（残基35-39）和β链（残基40-49）。通过EPR对7.8、8.4和9.6 nm rHDL的残基14、19、34、37、41和58进行了检查，以评估粒度对N-末端结构的影响。残基14、19和58没有显示出显著的rHDL大小依赖性光谱或可及性差异，而残基34、37和41显示出中度光谱变化，沿着实质性的rHDL大小依赖性分子可及性差异。我们已经阐明了9.6 nm rHDL（残基6-98）的apoA-I的N-末端结构域的二级结构，并确定了该区域中受颗粒大小影响的残基。我们得出结论，螺旋间段（残基35-49）在apoA-I的适应HDL的颗粒大小中发挥作用。
Apolipoprotein A-I (apoA-I) is the major protein component of high density lipoproteins (HDL) and a critical element of cholesterol metabolism. To better elucidate the role of the apoA-I structure-function in cholesterol metabolism, the conformation of the apoA-I N terminus (residues 6-98) on nascent HDL was examined by electron paramagnetic resonance (EPR) spectroscopic analysis. A series of 93 apoA-I variants bearing single nitroxide spin label at positions 6-98 was reconstituted onto 9.6-nm HDL particles (rHDL). These particles were subjected to EPR spectral analysis, measuring regional flexibility and side chain solvent accessibility. Secondary structure was elucidated from side-chain mobility and molecular accessibility, wherein two major alpha-helical domains were localized to residues 6-34 and 50-98. We identified an unstructured segment (residues 35-39) and a beta-strand (residues 40-49) between the two helices. Residues 14, 19, 34, 37, 41, and 58 were examined by EPR on 7.8, 8.4, and 9.6 nm rHDL to assess the effect of particle size on the N-terminal structure. Residues 14, 19, and 58 showed no significant rHDL size-dependent spectral or accessibility differences, whereas residues 34, 37, and 41 displayed moderate spectral changes along with substantial rHDL size-dependent differences in molecular accessibility. We have elucidated the secondary structure of the N-terminal domain of apoA-I on 9.6 nm rHDL (residues 6-98) and identified residues in this region that are affected by particle size. We conclude that the inter-helical segment (residues 35-49) plays a role in the adaptation of apoA-I to the particle size of HDL.