The Mina and Everard Goodman Faculty of Life Sciences , Bar-Ilan University , Ramat-Gan 5290002 , Israel.
Baker Laboratory of Chemistry and Chemical Biology , Cornell University , Ithaca , New York 14853-1301 , United States.
J Phys Chem B. 2018 May 10;122(18):4793-4801. doi: 10.1021/acs.jpcb.8b02181. Epub 2018 May 2.
The microscopic-order-macroscopic-disorder (MOMD) approach for H NMR line shape analysis is applied to dry and hydrated 3-fold- and 2-fold-symmetric amyloid-Aβ fibrils and protofibrils of the D23N mutant. The methyl moieties of L17, L34, V36 (C-CD), and M35 (S-CD) serve as probes. Experimental H spectra acquired previously in the 147-310 K range are used. MOMD describes local probe motion as axial diffusion ( R tensor) in the presence of a potential, u, which represents the spatial restrictions exerted by the molecular surroundings. We find that R = (0.2-3.3) × 10 s, R = (2.2-2.5) × 10 s, and R is tilted from the H quadrupolar tensor at 60-75°. The strength of u is in the (2.0-2.4) kT range; its rhombicity is substantial. The only methyl moieties affected by fibril hydration are those of M35, located at fibril interfaces. The associated local potentials change form abruptly around 260 K, where massive water freezing occurs. An independent study revealed unfrozen "tightly-peptide-bound" water residing at the interfaces of the 3-fold-symmetric Aβ fibrils and at the interfaces of the E22G and E22Δ Aβ-mutant fibrils. Considering this to be the case in general for Aβ-related fibrils, the following emerges. The impact of water freezing is transmitted selectively to the fibril structure through interactions with tightly-peptide-bound water, in this case of M35 methyl moieties. The proof that such waters reside at the interfaces of the 2-fold-symmetric fibril, and the protofibril of the D23N mutant, is new. MOMD provides information on the surroundings of the NMR probe directly via the potential, u, which is inherent to the model; a prior interpretation of the same experimental data does so partially and indirectly (see below). Thus, MOMD analysis of NMR line shapes as applied to amyloid fibrils/protein aggregates emerges as a consistent new tool for elucidating the properties of, and processes associated with, molecular environments in the fibril.
采用微观有序-宏观无序（MOMD）方法对 3 倍和 2 倍对称的淀粉样蛋白 Aβ纤维和 D23N 突变体原纤维中的干燥和水合 L17、L34、V36（C-CD）和 M35（S-CD）的甲基部分进行 H NMR 线宽分析。以前在 147-310 K 范围内获得的实验 H 谱用于该研究。MOMD 将局部探针运动描述为轴向扩散（R 张量），同时存在一个表示分子环境施加的空间限制的势，u。我们发现 R =（0.2-3.3）×10 s，R =（2.2-2.5）×10 s，R 相对于 H 四极张量倾斜 60-75°。势 u 的强度在（2.0-2.4）kT 范围内；其各向异性较大。仅受纤维水合影响的甲基部分是位于纤维界面处的 M35。相关的局部势在 260 K 左右突然改变，此时大量水冻结。一项独立的研究表明，“紧密肽结合”水在 3 倍对称 Aβ纤维的界面处以及 E22G 和 E22Δ Aβ-突变纤维的界面处处于未冻结状态。考虑到这通常是 Aβ 相关纤维的情况，因此得出以下结论。水冻结的影响通过与紧密肽结合水的相互作用选择性地传递到纤维结构中，在这种情况下是 M35 甲基部分。证明这种水存在于 2 倍对称纤维和 D23N 突变体原纤维的界面处是新的。MOMD 通过模型固有的势 u 直接提供 NMR 探针周围环境的信息，这是一种直接的方法；对相同实验数据的先前解释部分且间接（见下文）地做到了这一点。因此，应用于淀粉样蛋白纤维/蛋白聚集体的 NMR 线宽的 MOMD 分析成为阐明纤维中分子环境的特性和相关过程的一致新工具。
