Protective hinge in insulin opens to enable its receptor engagement
Protective hinge in insulin opens to enable its receptor engagement
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DOI：
10.1073/pnas.1412897111
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发表时间：
2014-08-19
影响因子：
11.1
通讯作者：
Lawrence, Michael C.
中科院分区：
文献类型：
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作者：
Menting, John G.;Yang, Yanwu;Lawrence, Michael C.
胰岛素提供了球状蛋白的经典模型，但激素如何改变构象以与其受体结合长期以来一直是个谜。人们的兴趣集中在 C 端 B 链片段，它对于 β 细胞的保护性自组装和靶组织的受体结合至关重要。可以从重建主要激素结合位点（α亚基结构域 L1 和 α CT）的截短“微受体”中获得洞察力。我们证明，在微受体结合时，该片段在其 B20-B23 β 转角处经历一致的铰链状旋转，将 Phe(B24) 的重新定向与 B25-B28 β 链远离激素核心的 60 度旋转耦合，以与受体的 L1-β(2) 片反平行。该铰链的打开使保守的非极性侧链（Ile(A2)、Val(A3)、Val(B12)、Phe(B24) 和 Phe(B25)）与受体结合。通过非标准诱变来限制铰链可以保留天然折叠，但会阻止受体结合，而其工程化开放则以蛋白质不稳定和非天然聚集为代价来维持活性。我们的研究结果合理化了胰岛素家族临床突变的特性，并为设计治疗类似物提供了先前未知的基础。我们设想胰岛素的游离构象和受体结合构象之间的转换是作为生物合成和功能的冲突结构决定因素的解决方案。
Insulin provides a classical model of a globular protein, yet how the hormone changes conformation to engage its receptor has long been enigmatic. Interest has focused on the C-terminal B-chain segment, critical for protective self-assembly in beta cells and receptor binding at target tissues. Insight may be obtained from truncated "microreceptors" that reconstitute the primary hormone- binding site (alpha-subunit domains L1 and alpha CT). We demonstrate that, on microreceptor binding, this segment undergoes concerted hinge-like rotation at its B20-B23 beta-turn, coupling reorientation of Phe(B24) to a 60 degrees rotation of the B25-B28 beta-strand away from the hormone core to lie antiparallel to the receptor's L1-beta(2) sheet. Opening of this hinge enables conserved nonpolar side chains (Ile(A2), Val(A3), Val(B12), Phe(B24), and Phe(B25)) to engage the receptor. Restraining the hinge by nonstandard mutagenesis preserves native folding but blocks receptor binding, whereas its engineered opening maintains activity at the price of protein instability and nonnative aggregation. Our findings rationalize properties of clinical mutations in the insulin family and provide a previously unidentified foundation for designing therapeutic analogs. We envisage that a switch between free and receptor-bound conformations of insulin evolved as a solution to conflicting structural determinants of biosynthesis and function.