Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Sakyo-Ku, Kyoto, 606-8502, Japan.
Institute for Integrated Radiation and Nuclear Science, Kyoto University, Sennan, Osaka, 590-0494, Japan.
Biochem Biophys Res Commun. 2022 Sep 17;621:162-167. doi: 10.1016/j.bbrc.2022.07.010. Epub 2022 Jul 7.
Amyloid β-protein (Aβ) oligomers are involved in the early stages of Alzheimer's disease (AD) and antibodies against these toxic oligomers could be useful for accurate diagnosis of AD. We identified the toxic conformer of Aβ42 with a turn at positions 22/23, which has a propensity to form toxic oligomers. The antibody 24B3, developed by immunization of a toxic conformer surrogate E22P-Aβ9-35 in mice, was found to be useful for AD diagnosis using human cerebrospinal fluid (CSF). However, it is not known how 24B3 recognizes the toxic conformation of wild-type Aβ in CSF. Here, we report the crystal structure of 24B3 Fab complexed with E22P-Aβ11-34, whose residues 16-26 were observed in electron densities, suggesting that the residues comprising the toxic turn at positions 22/23 were recognized by 24B3. Since 24B3 bound only to Aβ42 aggregates, several conformationally restricted analogs of Aβ42 with an intramolecular disulfide bond to mimic the conformation of toxic Aβ42 aggregates were screened by enzyme immunoassay. As a result, only F19C,A30homoC-SS-Aβ42 (1) bound significantly to 24B3. These data provide a structural basis for its low affinity to the Aβ42 monomer and selectivity for its aggregate form.
淀粉样β蛋白（Aβ）寡聚体参与阿尔茨海默病（AD）的早期阶段，针对这些毒性寡聚体的抗体可能有助于 AD 的准确诊断。我们鉴定出具有 22/23 位转折的 Aβ42 毒性构象，其具有形成毒性寡聚体的倾向。通过在小鼠中免疫毒性构象替代物 E22P-Aβ9-35 而开发的抗体 24B3 被发现可用于使用人脑脊液（CSF）进行 AD 诊断。然而，目前尚不清楚 24B3 如何识别 CSF 中野生型 Aβ 的毒性构象。在这里，我们报告了 24B3 Fab 与 E22P-Aβ11-34 复合物的晶体结构，其残基 16-26 在电子密度中观察到，表明 24B3 识别构成 22/23 位毒性转折的残基。由于 24B3 仅与 Aβ42 聚集物结合，因此通过酶免疫测定筛选了几种具有分子内二硫键以模拟毒性 Aβ42 聚集物构象的 Aβ42 构象受限类似物。结果，只有 F19C,A30homoC-SS-Aβ42（1）与 24B3 显著结合。这些数据为其对 Aβ42 单体的低亲和力和对其聚集形式的选择性提供了结构基础。
