Congdon Erin E, Kim Sohee, Bonchak Jonathan, Songrug Tanakorn, Matzavinos Anastasios, Kuret Jeff
Center for Molecular Neurobiology, Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA.
J Biol Chem. 2008 May 16;283(20):13806-16. doi: 10.1074/jbc.M800247200. Epub 2008 Mar 21.
Filamentous inclusions composed of the microtubule-associated protein tau are found in Alzheimer disease and other tauopathic neurodegenerative diseases, but the mechanisms underlying their formation from full-length protein monomer under physiological conditions are unclear. To address this issue, the fibrillization of recombinant full-length four-repeat human tau was examined in vitro as a function of time and submicromolar tau concentrations using electron microscopy assay methods and a small-molecule inducer of aggregation, thiazine red. Data were then fit to a simple homogeneous nucleation model with rate constant constraints established from filament dissociation rate, critical concentration, and mass-per-unit length measurements. The model was then tested by comparing the predicted time-dependent evolution of length distributions to experimental data. Results indicated that once assembly-competent conformations were attained, the rate-limiting step in the fibrillization pathway was tau dimer formation. Filament elongation then proceeded by addition of tau monomers to nascent filament ends. Filaments isolated at reaction plateau contained approximately 2 tau protomers/beta-strand spacing on the basis of mass-per-unit length measurements. The model suggests four key steps in the aggregation pathway that must be surmounted for tau filaments to form in disease.
由微管相关蛋白tau组成的丝状内含物在阿尔茨海默病和其他tau蛋白病性神经退行性疾病中被发现，但在生理条件下其从全长蛋白单体形成的潜在机制尚不清楚。为了解决这个问题，使用电子显微镜检测方法和一种聚集小分子诱导剂噻嗪红，体外研究了重组全长四重复人tau的纤维化过程，该过程是时间和亚微摩尔tau浓度的函数。然后将数据拟合到一个简单的均匀成核模型，该模型具有根据丝解离速率、临界浓度和单位长度质量测量建立的速率常数约束。然后通过将预测的长度分布随时间的演变与实验数据进行比较来测试该模型。结果表明，一旦获得具有组装能力的构象，纤维化途径中的限速步骤就是tau二聚体的形成。然后通过向新生丝末端添加tau单体来进行丝的延长。根据单位长度质量测量，在反应平台期分离的丝在每个β链间距中大约含有2个tau原纤维。该模型表明了聚集途径中的四个关键步骤，tau丝要在疾病中形成就必须克服这些步骤。
