Spontaneous deamidation prompted backbone isomerization of Asn/Asp residues resulting in – most cases – the insertion of an extra methylene group into the backbone poses a threat to the structural integrity of proteins. Here we present a systematical analysis of how temperature, pH, presence of charged residues, but most importantly backbone conformation and dynamics affect isomerization rates as determined by nuclear magnetic resonance in the case of designed peptide-models. We demonstrate that restricted mobility (such as being part of a secondary structural element) may safeguard against isomerization, but this protective factor is most effective in the case of off-pathway folds which can slow the reaction by several magnitudes compared to their on-pathway counterparts. We show that the geometric descriptors of the initial nucleophilic attack of the isomerization can be used to classify local conformation and contribute to the design of stable protein drugs, antibodies or the assessment of the severity of mutations.

中文翻译：

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非通路 3D 结构可防止自发 Asn/Asp 异构化：屏蔽蛋白质阿喀琉斯之踵

自发脱酰胺促进 Asn/Asp 残基的主链异构化，导致 - 大多数情况下 - 额外的亚甲基插入主链对蛋白质的结构完整性构成威胁。在这里，我们系统地分析了温度、pH、带电残基的存在，但最重要的是主链构象和动力学如何影响异构化速率，这是在设计的肽模型的情况下由核磁共振确定的。我们证明了受限的流动性（例如作为二级结构元素的一部分）可以防止异构化，但这种保护因素在非路径折叠的情况下最有效，与它们的路径相比，它可以将反应减慢几个数量级同行。