High-resolution structure of intramolecularly proteolyzed human mucin-1 SEA domain
High-resolution structure of intramolecularly proteolyzed human mucin-1 SEA domain
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DOI：
10.1016/j.bbapap.2020.140361
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发表时间：
2020-03-01
影响因子：
3.2
通讯作者：
Ermacora，Mario R.
中科院分区：
文献类型：
--
作者：
Noguera，Martin E.;Jakoncic，Jean;Ermacora，Mario R.
海洋结构域在与高度糖基化环境相关的大蛋白中普遍存在。某些海区经历分子内蛋白质分解，涉及丝氨酸羟基对上一个甘氨酸羰基的亲核攻击。粘蛋白-1(MUC1)SEA结构域作为分子内蛋白降解的模型已被广泛研究。由于在MUC1SEA中既不能确定一般的碱、一般的酸，也不能确定氧阴离子空穴，所以有人认为蛋白质的降解是由于蛋白质折叠所致的剪切肽键的非平面性所加速的。反应物扭曲的多肽键也被用来解释几个无关蛋白质的自蛋白分解。然而，MUC1SEA中多肽扭曲的唯一证据来自对反应物的分子动力学模拟，模拟的是切割产物的单一核磁共振结构。我们首次报道了裂解的MUC1SEA的高分辨X射线结构。与未裂解海区的结构比较表明，进化上插入MUC1海裂解环中的残基数量排除了适当的氢键贝塔转角的形成。通过序列分析，我们发现所有已知的裂解SEA结构域都存在这种构象受挫。此外，可以模拟未切割的前体的替代构象，其中可剪断的多肽键是平面的。结合前人对自蛋白水解酶的研究，讨论了这些结构对自蛋白水解酶的影响。
SEA domains are ubiquitous in large proteins associated with highly glycosylated environments. Certain SEA domains undergo intramolecular proteolysis involving a nucleophilic attack of a serine hydroxyl group on the preceding glycine carbonyl. The mucin-1 (MUC1) SEA domain has been extensively investigated as a model of intramolecular proteolysis. Since neither a general base, a general acid, nor an oxyanion hole could be identified in MUC1 SEA, it has been suggested that proteolysis is accelerated by a non-planarity of the scissile peptide bond imposed by protein folding. A reactant distorted peptide bond has been also invoked to explain the autoproteolysis of several unrelated proteins. However, the only evidence of peptide distortion in MUC1 SEA stems from molecular dynamic simulations of the reactant modeled upon a single NMR structure of the cleaved product. We report the first high-resolution X-ray structure of cleaved MUC1 SEA. Structural comparison with uncleaved SEA domains suggests that the number of residues evolutionarily inserted in the cleaved loop of MUC1 SEA precludes the formation of a properly hydrogen-bonded beta turn. By sequence analysis, we show that this conformational frustration is shared by all known cleaved SEA domains. In addition, alternative conformations of the uncleaved precursor could be modeled in which the scissile peptide bond is planar. The implications of these structures for autoproteolysis are discussed in the light of the previous research on autoproteolysis.