Capturing the Hemoglobin Allosteric Transition in a Single Crystal Form
Capturing the Hemoglobin Allosteric Transition in a Single Crystal Form
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以单晶形式捕获血红蛋白变构转变
DOI：
10.1021/ja500380e
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发表时间：
2014
影响因子：
15
通讯作者：
and Sam-Yong Park.
中科院分区：
文献类型：
--
作者：
Naoya Shibayama;Kanako Sugiyama;Jeremy R. H. Tame;and Sam-Yong Park.
许多寡聚蛋白质中的变构被假定通过配体结合驱动的从紧张（T）到松弛（R）状态的构象转变而发生，这主要基于对血红蛋白的结构和功能的了解，血红蛋白是所有变构蛋白中研究最彻底的。然而，越来越多的证据表明，血红蛋白在两种终态之间具有多种中间体。由于这些中间形式与动态平衡中的最终状态共存，并且不能通过常规技术单独表征，因此对其性质和功能知之甚少。在这里，我们提出了完整的结构和功能快照的9个平衡构象的人血红蛋白在半配体和完全配体状态下，通过使用一种新的组合的X射线衍射分析和显微分光光度O2平衡测量三个同晶晶体，每个捕获三个不同的平衡构象。值得注意的是，这种晶体形式的构象组根据变构平衡的变化而变化，反映了血红蛋白连接状态和结晶溶液条件的差异。我们发现，9个快照结构覆盖了血红蛋白的完整构象空间，范围从T到R2（第二个放松的四级结构）通过R，与R和R2之间的各种放松的中间形式。此外，我们发现了一个以前身份不明的中间构象，T和R之间，与中间O2亲和力，寻求许多研究小组在一段时间的几十年。这些发现揭示了人血红蛋白的平衡构象和过渡途径的全面图片。
Allostery in many oligomeric proteins has been postulated to occur via a ligand-binding-driven conformational transition from the tense (T) to relaxed (R) state, largely on the basis of the knowledge of the structure and function of hemoglobin, the most thoroughly studied of all allosteric proteins. However, a growing body of evidence suggests that hemoglobin possesses a variety of intermediates between the two end states. As such intermediate forms coexist with the end states in dynamic equilibrium and cannot be individually characterized by conventional techniques, very little is known about their properties and functions. Here we present complete structural and functional snapshots of nine equilibrium conformers of human hemoglobin in the half-liganded and fully liganded states by using a novel combination of X-ray diffraction analysis and microspectrophotometric O2equilibrium measurements on three isomorphous crystals, each capturing three distinct equilibrium conformers. Notably, the conformational set of this crystal form varies according to shifts in the allosteric equilibrium, reflecting the differences in hemoglobin ligation state and crystallization solution conditions. We find that nine snapshot structures cover the complete conformational space of hemoglobin, ranging from T to R2 (the second relaxed quaternary structure) through R, with various relaxed intermediate forms between R and R2. Moreover, we find a previously unidentified intermediate conformer, between T and R, with an intermediate O2affinity, sought by many research groups over a period of decades. These findings reveal a comprehensive picture of the equilibrium conformers and transition pathway for human hemoglobin.