A comparative NMR study of the polypeptide backbone dynamics of hemoglobin in the deoxy and carbonmonoxy forms.
A comparative NMR study of the polypeptide backbone dynamics of hemoglobin in the deoxy and carbonmonoxy forms.
复制标题
脱氧和单氧碳形式血红蛋白的多肽主链动力学的比较核磁共振研究。
DOI：
10.1021/bi602654u
复制
发表时间：
2007
期刊：
影响因子：
2.9
通讯作者：
Ho,Chien
中科院分区：
文献类型：
--
作者：
Song,Xiang-Jin;Yuan,Yue;Simplaceanu,Virgil;Sahu,SarataChandra;Ho,NancyT;Ho,Chien
基于无模型的NMR动力学研究已经对多肽骨架酰胺N-H键载体进行了链特异性、同位素的脱氧和碳单氧基形式的研究。使用15 N-弛豫参数[纵向弛豫速率（R1），横向弛豫速率（R2），在两种温度（29和34 °C）和两种磁场强度（11.7和14.1 T）下测量的异源核Overhauser效应（NOE）。在人类正常成人血红蛋白（Hb A）的脱氧和一碳氧形式中，大多数氨基酸残基的酰胺N-H键在快速时间尺度（纳秒到皮秒）上是刚性的，除了环区域和某些螺旋-螺旋连接。尽管β 146 His在脱氧血红蛋白A中是刚性的，但已发现其在CO形式中不受其主链运动的限制，这可能是由于其氢键/盐桥网络的断裂。我们现在有直接的动力学证据的Hb在溶液中的这种结构转变。虽然在脱氧状态下具有显著的柔性，但在二聚体内（α1β1）界面中的邻居α 31 Arg和β 123 Thr在CO结合时表现出硬化。这些发现暗示了α 31 Arg和β 123 Thr在二聚体内通讯中的作用，但与X射线晶体学的结果相矛盾。我们还发现，在二聚体内（α1β1）界面中存在相当大的灵活性（即，B、G和H螺旋和GH角）和可能涉及几个氨基酸残基（例如，α 31 Arg、β3Leu、β 41 Phe、β 123 Thr和β 146 His）。二聚体内界面的几个氨基酸残基，如β 109 Val，似乎参与了可能的构象交换过程。本研究的动态图片提供了新的见解到传统的描述的立体化学机制的合作氧合的血红蛋白A的基础上的X-射线晶体学结果。
Model-free-based NMR dynamics studies have been undertaken for polypeptide backbone amide N−H bond vectors for both the deoxy and carbonmonoxy forms of chain-specific, isotopically (15N and2H) labeled tetrameric hemoglobin (Hb) using15N-relaxation parameters [longitudinal relaxation rate (R1), transverse relaxation rate (R2), and heteronuclear nuclear Overhauser effect (NOE)] measured at two temperatures (29 and 34 °C) and two magnetic field strengths (11.7 and 14.1 T). In both deoxy and carbonmonoxy forms of human normal adult hemoglobin (Hb A), the amide N−H bonds of most amino acid residues are rigid on the fast time scale (nanosecond to picosecond), except for the loop regions and certain helix−helix connections. Although rigid in deoxy-Hb A, β146His has been found to be free from restriction of its backbone motions in the CO form, presumably due to the rupture of its hydrogen bond/salt bridge network. We now have direct dynamics evidence for this structural transition of Hb in solution. While remarkably flexible in the deoxy state, α31Arg and β123Thr, neighbors in the intradimer (α1β1) interface, exhibit stiffening upon CO binding. These findings imply a role for α31Arg and β123Thr in the intradimer communication but contradict the results from X-ray crystallography. We have also found that there is considerable flexibility in the intradimer (α1β1) interface (i.e., B, G, and H helices and the GH corner) and possible involvement of several amino acid residues (e.g., α31Arg, β3Leu, β41Phe, β123Thr, and β146His) in the allosteric pathway. Several amino acid residues at the intradimer interfaces, such as β109Val, appear to be involved in possible conformational exchange processes. The dynamic picture derived from the present study provides new insights into the traditional description of the stereochemical mechanism for the cooperative oxygenation of Hb A based on X-ray crystallographic results.