Department of Biochemistry, Bose Institute, P1/12 CIT Scheme VIIM, Kolkata 700054, India.
Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S.C. Mullick Road, Jadavpur, Kolkata 700032, India.
ACS Chem Neurosci. 2023 Aug 16;14(16):2888-2901. doi: 10.1021/acschemneuro.3c00281. Epub 2023 Aug 3.
The oligomeric form of amyloid-β peptide (Aβ42) plays a crucial role in the pathogenesis of Alzheimer's disease (AD) and is responsible for cognitive deficits. The soluble oligomers are believed to be more toxic compared to the fibril form. Protein--isoaspartyl methyltransferase (PIMT) is a repair enzyme that converts aberrant isoAsp residues, formed spontaneously on isomerization of normal Asp and Asn residues, back to typical Asp. It was shown to inhibit the fibrillization of Aβ42 (containing three Asp residues), and here, we investigate its effect on the size, conformation, and toxicity of Aβ42 oligomers (AβO). Far-UV CD indicated a shift in the conformational feature of AβOs from the random coil to β-sheet in the presence of PIMT. Binding of bis-ANS to different AβOs (obtained using different concentrations of Aβ42 monomer) indicated the correlation of size of oligomers to hydrophobicity: the smallest AβO having the highest hydrophobicity is the most toxic. Dynamic light scattering showed an increase in size of AβO with the addition of PIMT, a contrasting role to that on Aβ fibril. Assays using PC12-derived neurons showed the neuroprotective role of PIMT against AβO-induced toxicity. Furthermore, we have elaborated on the molecular mechanism of the antifibrillar action of PIMT and how this function is correlated with its enzymatic activity. PIMT has a more pronounced effect on AβO as compared to a small heat shock protein, pointing to its importance for the amelioration of the adverse effect of both Aβ42 oligomers and fibrils.
淀粉样β肽（Aβ42）的寡聚形式在阿尔茨海默病（AD）的发病机制中起着至关重要的作用，并且与认知缺陷有关。与纤维形式相比，可溶性寡聚体被认为更具毒性。蛋白异天冬氨酸甲基转移酶（PIMT）是一种修复酶，可将正常天冬氨酸和天冬酰胺残基异构化形成的异常异天冬氨酸残基转换回典型的天冬氨酸。它被证明可以抑制 Aβ42（含有三个天冬氨酸残基）的纤维化，在这里，我们研究了它对 Aβ42 寡聚体（AβO）的大小、构象和毒性的影响。远紫外 CD 表明，在存在 PIMT 的情况下，AβOs 的构象特征从无规卷曲转变为β-折叠。双 ANS 与不同 AβOs（通过使用不同浓度的 Aβ42 单体获得）的结合表明寡聚物的大小与疏水性相关：具有最高疏水性的最小 AβO 是最毒的。动态光散射表明，随着 PIMT 的加入，AβO 的大小增加，与 Aβ 纤维的作用相反。使用 PC12 衍生神经元进行的测定表明，PIMT 对 AβO 诱导的毒性具有神经保护作用。此外，我们详细阐述了 PIMT 的抗纤维作用的分子机制，以及这种功能与其酶活性的相关性。与小热休克蛋白相比，PIMT 对 AβO 的影响更为明显，这表明它对于改善 Aβ42 寡聚体和纤维的不利影响非常重要。
