Conformational fluctuations in deoxy hemoglobin revealed as a major contributor to anionic modulation of function through studies of the oxygenation and oxidation of hemoglobins A0 and Deer Lodge beta2(NA2)His --> Arg.
Conformational fluctuations in deoxy hemoglobin revealed as a major contributor to anionic modulation of function through studies of the oxygenation and oxidation of hemoglobins A0 and Deer Lodge beta2(NA2)His --> Arg.
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DOI：
10.1021/bi971574s
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发表时间：
1998-01
期刊：
影响因子：
2.9
通讯作者：
C. Bonaventura;S. Tesh;K. Faulkner;D. Kraiter;A. L. Crumbliss
中科院分区：
文献类型：
--
作者：
C. Bonaventura;S. Tesh;K. Faulkner;D. Kraiter;A. L. Crumbliss
生物体依赖于分子水平的调节，例如通过阴离子对血红蛋白（Hb）功能的变构调节，以应对不断变化的环境和生理条件所带来的挑战。的氧合，氧化，和巯基反应性的血红蛋白的阴离子的影响的比较导致我们建议，一个大的和显着的一部分，由阴离子结合所带来的氧亲和力的转变发生的结果增加的构象刚性的T状态的脱氧血红蛋白。随着构象刚性增加，脱氧T-状态四聚体中的亚基变得越来越难以呈现更高的氧亲和力形式（T '，T”，T“'...）空间位阻较小。氧亲和力反映了T状态内快速平衡构象的平均值，并且当阴离子水平增加时相应地降低。Hb氧化的初始阶段对空间位阻变化相对不敏感，因此主要反映了四元（T，T '，T”，T“'...）均衡我们表明，空间遮蔽巯基的β 93半胱氨酸在脱氧血红蛋白的反应性是更大的无氯缓冲液比在缓冲液中添加氯化物。阴离子诱导的T-四级状态内的亚基的构象波动的程度和频率的降低，从而降低巯基反应性以及氧亲和力。这种平行的阴离子控制功能使我们能够测试，并反驳，在血红蛋白鹿洛奇中心腔的未补偿的正电荷增加的频率和程度的构象波动在其脱氧结构的可能性。这种血红蛋白的变体表现出增加阴离子的敏感性，增加氧的亲和力，并增加氧化的容易性，但没有增加其巯基的反应性，这表明在脱氧血红蛋白鹿洛奇的活性位点的改变主要是电子和不相关的构象波动增加在其T状态。通过添加阴离子恢复血红蛋白鹿小屋的正常性质加强了我们的结论，即阴离子控制可以通过空间和电子改变来发挥作用。血红蛋白的T状态内的波动的阴离子控制说明了大分子结构-功能关系的一个重要原则：功能调节可以通过构象刚性的改变来实现。
Organisms rely on regulation at the molecular level, such as the allosteric regulation of hemoglobin (Hb) function by anions, to meet challenges presented by changing environmental and physiological conditions. A comparison of the effects of anions on oxygenation, oxidation, and sulfhydryl reactivity of Hb leads us to suggest that a large and significant part of the shift in oxygen affinity brought about by anion binding occurs as a result of increased conformational rigidity of the T state of deoxy Hb. As conformational rigidity increases, it becomes increasingly difficult for subunits in the deoxygenated T-state tetramer to assume higher oxygen affinity forms (T', T", T"'...) with less steric hindrance. The oxygen affinity reflects the average of the rapidly equilibrating conformations within the T state and is correspondingly decreased when anion levels are increased. The initial stage of the oxidation of Hb is relatively insensitive to steric alterations and thus reflects, primarily, the electronic aspects of the quaternary (T, T', T", T"'...) equilibrium. We show that the reactivity of the sterically obscured sulfhydryl of beta93 Cys in deoxy Hb is much greater in chloride-free buffers than in buffers with added chloride. Anion-induced decreases in the extent and frequency of conformational fluctuations of subunits within the T-quaternary state thus reduce sulfhydryl reactivity as well as oxygen affinity. This parallel in anionic control of function allowed us to test, and disprove, the possibility that uncompensated positive charges in the central cavity of Hb Deer Lodge increase the frequency and extent of conformational fluctuations in its deoxy structure. This Hb variant exhibits increased anion sensitivity, increased oxygen affinity, and increased ease of oxidation, but without increased reactivity of its sulfhydryl groups, indicating that active-site alterations in deoxy Hb Deer Lodge are primarily electronic and not associated with increased conformational fluctuations within its T state. The restoration of normal properties in Hb Deer Lodge by addition of anions reinforces our conclusion that anionic control can be exerted through both steric and electronic alterations. The anionic control of fluctuations within the T state of Hb illustrates an important principle of macromolecular structure-function relationships: that functional regulation can be achieved by alterations in conformational rigidity.