Binger Katrina J, Pham Chi L L, Wilson Leanne M, Bailey Michael F, Lawrence Lynne J, Schuck Peter, Howlett Geoffrey J
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, 30 Flemington Road, Parkville, Victoria 3010, Australia.
J Mol Biol. 2008 Feb 29;376(4):1116-29. doi: 10.1016/j.jmb.2007.12.055. Epub 2008 Jan 3.
Alzheimer's and several other diseases are characterized by the misfolding and assembly of protein subunits into amyloid fibrils. Current models propose that amyloid fibril formation proceeds via the self-association of several monomers to form a nucleus, which then elongates by the addition of monomer to form mature fibrils. We have examined the concentration-dependent kinetics of apolipoprotein C-II amyloid fibril formation and correlated this with the final size distribution of the fibrils determined by sedimentation velocity experiments. In contrast to predictions of the nucleation-elongation model, the final size distribution of the fibrils was found to be relatively independent of the starting monomer concentration. To explain these results, we extended the nucleation-elongation model to include fibril breaking and rejoining as integral parts of the amyloid fibril assembly mechanism. The system was examined under conditions that affected the stability of the mature fibrils including the effect of dilution on the free pool of monomeric apolipoprotein C-II and the time-dependent recovery of fibril size following sonication. Antibody-labelling transmission electron microscopy studies provided direct evidence for spontaneous fibril breaking and rejoining. These studies establish the importance of breaking and rejoining in amyloid fibril formation and identify prospective new therapeutic targets in the assembly pathway.
阿尔茨海默病和其他几种疾病的特征是蛋白质亚基错误折叠并组装成淀粉样纤维。目前的模型认为，淀粉样纤维的形成是通过几个单体的自组装形成一个核，然后通过添加单体来延长形成成熟纤维。我们研究了载脂蛋白C-II淀粉样纤维形成的浓度依赖性动力学，并将其与沉降速度实验确定的纤维最终尺寸分布相关联。与成核-延长模型的预测相反，发现纤维的最终尺寸分布相对独立于起始单体浓度。为了解释这些结果，我们扩展了成核-延长模型，将纤维断裂和重新连接作为淀粉样纤维组装机制的组成部分。在影响成熟纤维稳定性的条件下对该系统进行了研究，包括稀释对单体载脂蛋白C-II自由池的影响以及超声处理后纤维尺寸随时间的恢复。抗体标记透射电子显微镜研究为纤维的自发断裂和重新连接提供了直接证据。这些研究确立了断裂和重新连接在淀粉样纤维形成中的重要性，并确定了组装途径中潜在的新治疗靶点。
