A Unified Scheme for Initiation and Conformational Adaptation of Human Apolipoprotein E N-terminal Domain upon Lipoprotein Binding and for Receptor Binding Activity
A Unified Scheme for Initiation and Conformational Adaptation of Human Apolipoprotein E N-terminal Domain upon Lipoprotein Binding and for Receptor Binding Activity
复制标题
DOI：
10.1074/jbc.m901012200
复制
发表时间：
2009-05-22
影响因子：
4.8
通讯作者：
Wang, Jianjun
中科院分区：
文献类型：
--
作者：
Sivashanmugam, Arun;Wang, Jianjun
我们在此报告了人载脂蛋白 E3 (apoE3-NT) 完整受体结合域的高分辨率 NMR 结构。与apoE-NT的晶体结构相似，NMR结构显示出细长的四螺旋束。然而，还观察到了其他独特的结构特征。晶体结构中缺失的 N 和 C 末端片段形成了与束具有广泛三级接触的 α 螺旋，将这些短螺旋定向在特定位置以实现受体结合活性。在束中观察到的几个隐藏的亲水残基战略性地位于螺旋 1 和 2 之间以及螺旋 3 和 4 之间，显着破坏了这些螺旋-螺旋界面的稳定性。此外，这些埋藏的亲水残基形成埋藏的氢键，这可能在特定的无脂螺旋束恢复中发挥关键作用。短螺旋，nHelix C，完全暴露在溶剂中并且几乎垂直于束。这种短螺旋可能在启动蛋白质-脂质相互作用中发挥关键作用，导致较弱的螺旋-螺旋界面处的束优选构象适应。这产生了具有两个螺旋叶（螺旋1和4以及螺旋2和3）的开放构象，这可能是受体结合活性的有效构象。因此，NMR结构提出了脂蛋白结合后apoE-NT的起始和螺旋束打开以及受体结合活性的统一方案。
We report here a high-resolution NMR structure of the complete receptor-binding domain of human apolipoprotein E3 (apoE3-NT). Similar to the crystal structure of apoE-NT, the NMR structure displayed an elongated four-helix bundle. However, additional unique structural features were also observed. The segments in the N and C termini, which were missing in the crystal structure, formed alpha-helices having extensive tertiary contacts with the bundle, which oriented these short helices at specific positions for receptor binding activity. Several buried hydrophilic residues observed in the bundle were located strategically between helices 1 and 2 and between helices 3 and 4, significantly destabilizing these helix-helix interfaces. In addition, these buried hydrophilic residues formed buried H-bonds, which may play a key role in specific lipid-free helix bundle recovery. A short helix, nHelix C, was fully solvent-exposed and nearly perpendicular to the bundle. This short helix likely plays a critical role in initiating protein-lipid interaction, causing a preferred conformational adaptation of the bundle at the weaker helix-helix interfaces. This produces an open conformation with two lobes of helices, helices 1 and 4 and helices 2 and 3, which may be the competent conformation for receptor binding activity. Thus, the NMR structure suggests a unified scheme for the initiation and helix bundle opening of apoE-NT upon lipoprotein-binding and for receptor binding activity.