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An Unusually Rapid Protein Backbone Modification Stabilizes the Essential Bacterial Enzyme MurA.
Biochemistry ( IF 2.9 ) Pub Date : 2020-09-15 , DOI: 10.1021/acs.biochem.0c00502
Tianze Zhang 1 , Kjetil Hansen 1 , Argyris Politis 1 , Manuel M Müller 1
Affiliation  

Proteins are subject to spontaneous rearrangements of their backbones. Most prominently, asparagine and aspartate residues isomerize to their β-linked isomer, isoaspartate (isoAsp), on time scales ranging from days to centuries. Such modifications are typically considered “molecular wear-and-tear”, destroying protein function. However, the observation that some proteins, including the essential bacterial enzyme MurA, harbor stoichiometric amounts of isoAsp suggests that this modification can confer advantageous properties. Here, we demonstrate that nature exploits an isoAsp residue within a hairpin to stabilize MurA. We found that isoAsp formation in MurA is unusually rapid and critically dependent on folding status. Moreover, perturbation of the isoAsp-containing hairpin via site-directed mutagenesis causes aggregation of MurA variants. Structural mass spectrometry revealed that this effect is caused by local protein unfolding in MurA mutants. Our findings demonstrate that MurA evolved to “mature” via a spontaneous post-translational incorporation of a β-amino acid, which raises the possibility that isoAsp-containing hairpins may serve as a structural motif of biological importance.

中文翻译:

异常快速的蛋白质主链修饰可稳定必需的细菌酶 MurA。

蛋白质的主链会发生自发重排。最突出的是,天冬酰胺和天冬氨酸残基异构化为其 β-连接异构体异天冬氨酸 (isoAsp),时间尺度从几天到几个世纪不等。这种修饰通常被认为是“分子磨损”,破坏蛋白质功能。然而,观察到一些蛋白质,包括必需的细菌酶 MurA,含有化学计量的 isoAsp,表明这种修饰可以赋予有利的特性。在这里,我们证明大自然利用发夹内的 isoAsp 残基来稳定 MurA。我们发现 MurA 中 isoAsp 的形成异常迅速,并且严重依赖于折叠状态。此外,通过定点诱变扰动含有 isoAsp 的发夹会导致 MurA 变体聚集。结构质谱分析表明,这种效应是由 MurA 突变体中局部蛋白质去折叠引起的。我们的研究结果表明,MurA 通过翻译后自发掺入 β-氨基酸进化到“成熟”,这提出了含 isoAsp 的发夹可能作为具有生物学重要性的结构基序的可能性。
更新日期:2020-10-06
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