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 β淀粉样蛋白（Aβ）42是一种易于聚集的肽，被认为是阿尔茨海默氏症的精液病原体 疾病Aβ42的一种常见翻译后修饰是其蛋氨酸（Met）35残基的氧化。 Met 35氧化是生理学相关的，其中大部分阿尔茨海默氏淀粉样斑块由Met 35氧化组成。 Aβ42-Met35SO。在老年痴呆症领域， Aβ42 Met 35氧化的生物物理学和生物学后果。因此，它被认为是两个 促进和抑制聚集，并且还声称其增强和降低毒性。 Aβ42 Met 35的氧化使硫成为手性。这意味着两个而不是一个Aβ42-Met 35 SO肽 是生产出来的。Aβ42-Met 35-（R）-SO和Aβ42-Met 35-（S）-SO之间的相互转化垒极高 高（我们使用量子化学方法计算为45.2 kcal/mol），并且这两种肽必须 在生理条件下被认为是不同的物种。两个立体化学稳定的手性 因此，在阿尔茨海默病领域从未考虑过Aβ42 Met 35氧化的硫差向异构体。 我们最近报道了一种基于超临界CO2的分离方案，该方案现在允许获得Met-（R）- SO和Met-（S）-SO（克），纯度超过99.5%。利用这些积木，我们 能够制备Ab 42-Met 35-（R）-SO和Ab 42-Met 35-（S）-SO手性硫差向异构体， 立体化学信息。在这里，我们建议确定硫手性影响的程度 Aβ42-Met 35-（R）-SO和Aβ42-Met 35-（S）-SO聚集、神经元摄取和毒性。我们亦建议 开发使用LC/MS和NMR组合测定Aβ42-Met 35-（R）-SO动力学的测定方法， 甲硫氨酸亚砜还原酶（MSR）A和B对β42-Met 35-（S）-SO的还原。 这里提出的研究有望解决一个长期存在的争议，关于功能 Aβ42 Met 35氧化的后果，并将为未来R 01资助的研究毒性的实验奠定基础。 Aβ42-Met 35-（R）-SO和Aβ42-Met 35-（S）-SO的作用及其通过MSRA和MSRB还原为Aβ42 在海马和皮层脑组织中，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.