Department of Chemistry, Keio University, Yokohama, 223-8522, Japan.
Division of Pharmacology, Faculty of Pharmacy, Keio University, Tokyo, 105-8512, Japan.
Free Radic Biol Med. 2020 Feb 1;147:187-199. doi: 10.1016/j.freeradbiomed.2019.12.017. Epub 2019 Dec 19.
Misfolded Cu/Zn-superoxide dismutase (SOD1) is a pathological species in a subset of amyotrophic lateral sclerosis (ALS). Oxidative stress is known to increase in affected spinal cords of ALS and is thus considered to cause damages on SOD1 leading to the misfolding and aggregation. Despite this, it still remains elusive what triggers misfolding of SOD1 under oxidizing environment. Here, we show that a thiol group of Cys111 in SOD1 is oxidized to a sulfenic acid with hydrogen peroxide and reveal that further dissociation of the bound metal ions from the oxidized SOD1 allows another free Cys residue (Cys6) to nucleophilically attack the sulfenylated Cys111. As a result, an intra-molecular disulfide bond forms between Cys6 and Cys111. Such an abnormal SOD1 with the non-canonical disulfide bond was conformationally extended with significant cytotoxicity as well as high propensity to aggregate. Taken together, we propose a new model of SOD1 misfolding under oxidizing environment, in which formation of the non-canonical intramolecular disulfide bond plays a pivotal role.
错误折叠的 Cu/Zn-超氧化物歧化酶（SOD1）是肌萎缩侧索硬化症（ALS）的一部分病理物种。已知氧化应激会增加 ALS 受影响脊髓中的氧化应激，因此被认为会对 SOD1 造成损伤，导致错误折叠和聚集。尽管如此，在氧化环境下是什么引发 SOD1 的错误折叠仍然难以捉摸。在这里，我们表明 SOD1 中的半胱氨酸残基 Cys111 的一个巯基被过氧化氢氧化为亚磺酸，并且揭示从氧化的 SOD1 进一步解离结合的金属离子允许另一个游离的半胱氨酸残基（Cys6）亲核攻击亚磺酰化的 Cys111。结果，在 Cys6 和 Cys111 之间形成分子内二硫键。具有非典型二硫键的这种异常 SOD1 具有构象延伸，具有显著的细胞毒性和高聚集倾向。总之，我们提出了一种在氧化环境下 SOD1 错误折叠的新模型，其中非典型的分子内二硫键的形成起着关键作用。
