Griffin Michael D W, Mok Melva L Y, Wilson Leanne M, Pham Chi L L, Waddington Lynne J, Perugini Matthew A, Howlett Geoffrey J
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
J Mol Biol. 2008 Jan 4;375(1):240-56. doi: 10.1016/j.jmb.2007.10.038. Epub 2007 Oct 22.
A common feature of many of the most important and prominent amyloid-forming proteins is their ability to bind lipids and lipid complexes. Lipids are ubiquitous components of disease-associated amyloid plaques and deposits in humans, yet the specific roles of lipid in the process of amyloid fibril formation are poorly understood. This study investigated the effect of phospholipids on amyloid fibril formation by human apolipoprotein (apo) C-II using phosphatidylcholine derivatives comprising acyl chains of up to 14 carbon atoms. Submicellar concentrations of short-chain phospholipids increase the rate of apoC-II fibril formation in an acyl-chain-length- and concentration-dependent fashion, while high micellar concentrations of phospholipids completely inhibited amyloid formation. At lower concentrations of soluble phospholipid complexes, fibril formation by apoC-II was only partially inhibited, and under these conditions, aggregation followed a two-phase process. Electron microscopy showed that the fibrils resulting from the second phase of aggregation were straight, cablelike, and about 13 nm wide, in contrast to the homogeneous twisted-ribbon morphology of apoC-II fibrils formed under lipid-free conditions. Seeding experiments showed that this alternative fibril structure could be templated both in the presence and in the absence of lipid complex, suggesting that the two morphologies result from distinct assembly pathways. Circular dichroism spectroscopy studies indicated that the secondary structural conformation within the straight-type and ribbon-type fibrils were distinct, further suggesting divergent assembly pathways. These studies show that phospholipid complexes can change the structural architecture of mature fibrils and generate new fibril morphologies with the potential to alter the in vivo behaviour of amyloid. Such lipid interactions may play a role in defining the structural features of fibrils formed by diverse amyloidogenic proteins.
许多最重要且突出的形成淀粉样蛋白的蛋白质的一个共同特征是它们结合脂质和脂质复合物的能力。脂质是人类疾病相关淀粉样斑块和沉积物中普遍存在的成分，然而脂质在淀粉样纤维形成过程中的具体作用却知之甚少。本研究使用包含多达14个碳原子酰基链的磷脂酰胆碱衍生物，研究了磷脂对人载脂蛋白（apo）C-II淀粉样纤维形成的影响。亚胶束浓度的短链磷脂以酰基链长度和浓度依赖性方式增加apoC-II纤维形成的速率，而高胶束浓度的磷脂则完全抑制淀粉样蛋白的形成。在较低浓度的可溶性磷脂复合物下，apoC-II的纤维形成仅受到部分抑制，在这些条件下，聚集遵循两相过程。电子显微镜显示，与无脂质条件下形成的apoC-II纤维的均匀扭曲带状形态不同，聚集第二阶段产生的纤维是直的、索状的，宽约13nm。接种实验表明，这种替代的纤维结构在有或无脂质复合物的情况下都可以被模板化，这表明这两种形态是由不同的组装途径产生的。圆二色光谱研究表明，直型和带状型纤维内的二级结构构象不同，进一步表明组装途径不同。这些研究表明，磷脂复合物可以改变成熟纤维的结构架构，并产生新的纤维形态，有可能改变淀粉样蛋白在体内的行为。这种脂质相互作用可能在定义由多种淀粉样蛋白生成蛋白形成的纤维的结构特征中起作用。
