Elucidation of the true picture of the hemoglobin allosteric equilibrium

蛋白质变构的分子机制主要是基于对血红蛋白(Hb)的了解，在T(紧张)和R(松弛)状态之间的两态跃迁。然而，仅用这两种状态不能充分地描述解Hb的平衡系综。在这里，我们报道了一种前所未有的晶体形式，其中Hb可以根据条件自由采用任何变构结构，同时允许在晶体中直接监控氧结合。我们确定了九种构象，其中包括T和R之间的一个新的中间体。我们的发现全面地描绘了Hb的平衡构象和过渡途径。

The molecular mechanisms of protein allostery have been attributed to the two-state transition between T (tense) and R (relaxed) states, based largely on the knowledge about hemoglobin (Hb). However, an equilibrium ensemble for solution Hb cannot be adequately described by just these two states. Here we report an unprecedented crystal form in which Hb is free to adopt any allosteric structure, depending on the conditions, and at the same time allows oxygen binding to be monitored directly in the crystal. We identify nine conformations including a new intermediate between T and R. Our findings give a comprehensive picture of the equilibrium conformers and transition pathway for Hb.