Okuyama Kayoko, Nishiura Chisato, Mizushima Fumie, Minoura Katsuhiko, Sumida Miho, Taniguchi Taizo, Tomoo Koji, Ishida Toshimasa
Osaka University of Pharmaceutical Sciences, Takatsuki, Osaka, Japan.
Behavioral and Medical Sciences Research Consortium, Akashi, Hyogo, Japan.
FEBS J. 2008 Apr;275(7):1529-1539. doi: 10.1111/j.1742-4658.2008.06312.x. Epub 2008 Feb 28.
Although one of the priorities in Alzheimer's research is to clarify the filament formation mechanism for the tau protein, it is still unclear how it is transformed from a normal structure in a neuron. To examine the linkage-dependent contribution of each repeat peptide (R1-R4) to filament formation of the three- or four-repeat microtubule-binding domain (MBD) in the tau protein, four two-repeat peptides (R12, R13, R23 and R34) and two three-repeat peptides (R123 and R234) were prepared, and their in vitro self-aggregation was investigated by thioflavin S fluorescence and circular dichroism measurements, and by electron microscopy in neutral buffer (pH 7.6). Comparison of these aggregation behaviors with previous results for single-repeat peptides and wild-type 3RMBD (R134) and 4RMBD (R1234) indicated that (a) the two-repeat R23, not the R2 or R3 single repeat, forms the core structure in self-aggregation of 4RMBD, whereas that of 3RMBD comprises the R3 single repeat, (b) co-existence of R1 and R4 repeats is necessary for the aggregation behavior inherent in 3RMBD and 4RMBD, whereas the R1 or R4 repeat alone functions as a repressor or modifier of the filament formation, (c) 4RMBD aggregation is accompanied by R1-driven transition from random and alpha-helix structures to a beta-sheet structure, whereas 3RMBD aggregation involves three-repeat R134-specific transition from a random structure to an alpha-helix structure without the participation of a beta-sheet structure, and (d) the peptides that include the R1 repeat form a long filament irrespective of the absence or presence of the R4 repeat, whereas those that include the R4 repeat, but not the R1 repeat, form a relatively short filament. To the best of our knowledge, a systematic study of the linkage-dependent contribution of each repeat peptide to the paired helical filament formation of tau MBD has not been carried out previously, and thus the present information is useful for understanding the essence of the filament formation of tau MBD.
尽管阿尔茨海默病研究的重点之一是阐明tau蛋白的纤维形成机制，但目前仍不清楚它是如何从神经元中的正常结构转变而来的。为了研究tau蛋白中每个重复肽段（R1-R4）对三重复或四重复微管结合结构域（MBD）纤维形成的连锁依赖性贡献，制备了四个两重复肽段（R12、R13、R23和R34）和两个三重复肽段（R123和R234），并通过硫黄素S荧光和圆二色性测量以及中性缓冲液（pH 7.6）中的电子显微镜研究了它们的体外自聚集。将这些聚集行为与之前单重复肽段以及野生型3RMBD（R134）和4RMBD（R1234）的结果进行比较，结果表明：（a）两重复的R23而非R2或R3单重复在4RMBD的自聚集中形成核心结构，而3RMBD的核心结构则由R3单重复组成；（b）R1和R4重复的共存对于3RMBD和4RMBD固有的聚集行为是必要的，而单独的R1或R4重复则作为纤维形成的抑制剂或调节剂；（c）4RMBD聚集伴随着由R1驱动的从随机和α-螺旋结构向β-折叠结构的转变，而3RMBD聚集涉及三重复R134特异性的从随机结构向α-螺旋结构的转变，且没有β-折叠结构的参与；（d）包含R1重复的肽段无论是否存在R4重复都会形成长纤维，而包含R4重复但不包含R1重复的肽段则形成相对较短的纤维。据我们所知，此前尚未对每个重复肽段对tau MBD双螺旋丝形成的连锁依赖性贡献进行系统研究，因此目前的信息有助于理解tau MBD纤维形成的本质。
