How Distinct are the two Chiral Sulfur Epimers of Amyloid Beta Met35 Sulfoxide in their Aggregation, Toxicity and Reactivity with Methionine Sulfoxide Reductases A and B?

摘要 淀粉样β蛋白(Aβ)42是一种易于聚集的多肽，被认为是阿尔茨海默氏症的原始病原体 疾病。Aβ42的一种常见的翻译后修饰是其在蛋氨酸(Met)35残基上的氧化。 Met35氧化与生理相关，阿尔茨海默氏症淀粉样斑块的很大一部分由 Aβ42-Met35SO。在阿尔茨海默氏症领域，关于这两个问题存在着显著的分歧 Aβ42Met35氧化的生物物理和生物学后果。因此，这两个国家都声称 促进和抑制聚集，也被认为既可以增强毒性，也可以降低毒性。 Aβ42Met35的氧化使硫手性。这意味着两个而不是一个Aβ42-Met35SO多肽 都被生产出来。β_(42)-Me_(35)-(R)-SO和β_(42-M_(35))-(S)-SO之间的相互转化势垒是非常强的 高(我们用量子化学方法计算出它为45.2千卡/摩尔)，这两个肽必须是 在生理条件下被认为是不同的物种。两种立体化学稳定性手性化合物的形成 因此，在阿尔茨海默氏症领域，从未考虑过β42Met35氧化。 我们最近报道了一种基于超临界二氧化碳的分离协议，现在可以获得Met-(R)- SO和Met-(S)-SO以克量计，纯度超过99.5%。使用这些构建块，我们可以 能够制备AB42-Met35-(R)-SO和AB42-Met35-(S)-SO手性硫异构体而不损失 立体化学信息。在这里，我们建议确定硫手性影响的程度 Aβ42-Met35-(R)-SO和Aβ42-Met35-(S)-SO聚集、神经元摄取和毒性。我们还建议 建立LC/MS和核磁共振相结合的分析方法来测量β42-Met35-(R)-SO和 甲硫氨酸亚砜还原酶A和B还原β42-甲基35-(S)-SO 这里提出的研究有望解决关于功能的长期争议 β42Met35氧化的后果，并将为未来由R01资助的研究毒性的实验奠定基础 β_(42)-Me_(35)-(R)-SO和A_(β)_42-Me_(35)-(S)-SO的作用及其通过MSRA和MSRB还原为Aβ_(42) 在海马区和大脑皮层组织中，以及动物模型中。

ABSTRACT Amyloid beta (Aβ)42 is an aggregation-prone peptide and a believed seminal etiological agent of Alzheimer’s Disease. A common post-translational modification of Aβ42 is its oxidation at the methionine (Met) 35 residue. Met35 oxidation is physiologically relevant, with a large portion of Alzheimer’s amyloid plaques made up of Aβ42-Met35SO. There is a remarkable level of disagreement in the Alzheimer’s field with regard to both biophysical and biological consequences of Aβ42 Met35 oxidation. As such, it has been claimed to both promote and suppress aggregation and it has also been claimed to both enhance and reduce toxicity. Oxidation of Aβ42 Met35 renders the sulfur chiral. This means that two and not one Aβ42-Met35SO peptides are produced. The interconversion barrier between Aβ42-Met35-(R)-SO and Aβ42-Met35-(S)-SO is extremely high (we calculated it as 45.2 kcal/mol using quantum chemical methods), and the two peptides have to be considered distinct species under physiological conditions. The formation of two stereochemically stable chiral sulfur epimers in consequence Aβ42 Met35 oxidation has never been considered in the Alzheimer’s field. We have recently reported a supercritical CO2-based separation protocol that now allows obtaining Met-(R)- SO and Met-(S)-SO in gram quantities with purities exceeding 99.5%. Using these building blocks, we were able to make the Ab42-Met35-(R)-SO and Ab42-Met35-(S)-SO chiral sulfur epimers with no loss of stereochemical information. Here we propose to determine the degree to which sulfur chirality influences Aβ42-Met35-(R)-SO and Aβ42-Met35-(S)-SO aggregation, neuronal uptake and toxicity. We also propose to develop assays that use a combination of LC/MS and NMR to measure kinetics of Aβ42-Met35-(R)-SO and Aβ42-Met35-(S)-SO reduction by methionine sulfoxide reductases (MSR) A and B. Research proposed here is expected to resolve a long-standing controversy with regard to the functional consequences of Aβ42 Met35 oxidation and will set the stage for future R01-funded experiments to study toxic actions of Aβ42-Met35-(R)-SO and Aβ42-Met35-(S)-SO and their reduction to Aβ42 through MSRA and MSRB in hippocampal and cortical brain tissue, as well as animal models.