Sciarretta Kimberly L, Gordon David J, Petkova Aneta T, Tycko Robert, Meredith Stephen C
Departments of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA.
Biochemistry. 2005 Apr 26;44(16):6003-14. doi: 10.1021/bi0474867.
Recent solid-state NMR data (1) demonstrate that Abeta(1)(-)(40) adopts a conformation in amyloid fibrils with two in-register, parallel beta-sheets, connected by a bend structure encompassing residues D(23)VGSNKG(29), with a close contact between the side chains of Asp23 and Lys28. We hypothesized that forming this bend structure might be rate-limiting in fibril formation, as indicated by the lag period typically observed in the kinetics of Abeta(1)(-)(40) fibrillogenesis. We synthesized Abeta(1)(-)(40)-Lactam(D23/K28), a congener Abeta(1)(-)(40) peptide that contains a lactam bridge between the side chains of Asp23 and Lys28. Abeta(1)(-)(40)-Lactam(D23/K28) forms fibrils similar to those formed by Abeta(1)(-)(40). The kinetics of fibrillogenesis, however, occur without the typical lag period, and at a rate approximately 1000-fold greater than is seen with Abeta(1)(-)(40) fibrillogenesis. The strong tendency toward self-association is also shown by size exclusion chromatography in which Abeta(1)(-)(40)-Lactam(D23/K28) forms oligomers even at concentrations of approximately 1-5 microM. Under the same conditions, Abeta(1)(-)(40) shows no detectable oligomers by size exclusion chromatography. Our data suggest that Abeta(1)(-)(40)-Lactam(D23/K28) could bypass an unfavorable folding step in fibrillogenesis, because the lactam linkage "preforms" a bendlike structure in the peptide. Consistent with this view Abeta(1)(-)(40) growth is efficiently nucleated by Abeta(1)(-)(40)-Lactam(D23/K28) fibril seeds.
最近的固态核磁共振数据（1）表明，β-淀粉样蛋白1-40（Abeta(1)(-)(40)）在淀粉样纤维中呈现出一种构象，具有两个对齐的平行β-折叠片层，由一个包含D(23)VGSNKG(29)残基的弯曲结构连接，Asp23和Lys28的侧链之间紧密接触。我们推测，形成这种弯曲结构可能是纤维形成过程中的限速步骤，这一点在Abeta(1)(-)(40)纤维形成动力学中通常观察到的延迟期得到了体现。我们合成了Abeta(1)(-)(40)-内酰胺（D23/K28），这是一种Abeta(1)(-)(40)肽的同类物，在Asp23和Lys28的侧链之间含有一个内酰胺桥。Abeta(1)(-)(40)-内酰胺（D23/K28）形成的纤维与Abeta(1)(-)(40)形成的纤维相似。然而，纤维形成的动力学过程没有典型的延迟期，且速率比Abeta(1)(-)(40)纤维形成快约1000倍。尺寸排阻色谱也显示出其强烈的自缔合倾向，其中Abeta(1)(-)(40)-内酰胺（D23/K28）即使在约1-5 microM的浓度下也会形成寡聚体。在相同条件下，尺寸排阻色谱未检测到Abeta(1)(-)(40)形成寡聚体。我们的数据表明，Abeta(1)(-)(40)-内酰胺（D23/K28）可以绕过纤维形成过程中一个不利的折叠步骤，因为内酰胺键在肽中“预形成”了一个类似弯曲的结构。与这一观点一致的是，Abeta(1)(-)(40)的生长可被Abeta(1)(-)(40)-内酰胺（D23/K28）纤维种子有效地成核。
