School of Biological and Behavioural Sciences, Queen Mary, University of London, London, United Kingdom.
School of Biological and Behavioural Sciences, Queen Mary, University of London, London, United Kingdom.
J Biol Chem. 2022 Jul;298(7):102071. doi: 10.1016/j.jbc.2022.102071. Epub 2022 May 25.
Alzheimer's disease (AD) involves the neurotoxic self-assembly of a 40 and 42 residue peptide, Amyloid-β (Aβ). Inherited early-onset AD can be caused by single point mutations within the Aβ sequence, including Arctic (E22G) and Italian (E22K) familial mutants. These mutations are heterozygous, resulting in an equal proportion of the WT and mutant Aβ isoform expression. It is therefore important to understand how these mixtures of Aβ isoforms interact with each other and influence the kinetics and morphology of their assembly into oligomers and fibrils. Using small amounts of nucleating fibril seeds, here, we systematically monitored the kinetics of fibril formation, comparing self-seeding with cross-seeding behavior of a range of isoform mixtures of Aβ42 and Aβ40. We confirm that Aβ40(WT) does not readily cross-seed Aβ42(WT) fibril formation. In contrast, fibril formation of Aβ40(Arctic) is hugely accelerated by Aβ42(WT) fibrils, causing an eight-fold reduction in the lag-time to fibrillization. We propose that cross-seeding between the more abundant Aβ40(Arctic) and Aβ42(WT) may be important for driving early-onset AD and will propagate fibril morphology as indicated by fibril twist periodicity. This kinetic behavior is not emulated by the Italian mutant, where minimal cross-seeding is observed. In addition, we studied the cross-seeding behavior of a C-terminal-amidated Aβ42 analog to probe the coulombic charge interplay between Glu22/Asp23/Lys28 and the C-terminal carboxylate. Overall, these studies highlight the role of cross-seeding between WT and mutant Aβ40/42 isoforms, which can impact the rate and structure of fibril assembly.
阿尔茨海默病（AD）涉及到 40 个和 42 个残基肽的神经毒性自组装，即淀粉样β（Aβ）。早发性 AD 的遗传可以由 Aβ 序列中的单个点突变引起，包括北极（E22G）和意大利（E22K）家族突变体。这些突变是杂合的，导致 WT 和突变 Aβ 同工型的表达比例相等。因此，了解这些 Aβ 同工型的混合物如何相互作用并影响它们聚集成寡聚物和原纤维的动力学和形态非常重要。使用少量的成核原纤维种子，我们在这里系统地监测了原纤维形成的动力学，比较了 Aβ42 和 Aβ40 的一系列同工型混合物的自种和交叉种行为。我们证实 Aβ40（WT）不易交叉种 Aβ42（WT）原纤维形成。相比之下，Aβ40（北极）原纤维的形成被 Aβ42（WT）原纤维大大加速，导致原纤维形成的潜伏期减少了八倍。我们提出，更丰富的 Aβ40（北极）和 Aβ42（WT）之间的交叉种可能对驱动早发性 AD 很重要，并将传播原纤维形态，如原纤维扭曲周期性所表明的那样。这种动力学行为不能被意大利突变体模拟，在那里观察到最小的交叉种。此外，我们研究了 C 末端酰胺化的 Aβ42 类似物的交叉种行为，以探究 Glu22/Asp23/Lys28 和 C 末端羧酸盐之间的库仑电荷相互作用。总的来说，这些研究强调了 WT 和突变 Aβ40/42 同工型之间交叉种的作用，这可能会影响原纤维组装的速度和结构。
