UV resonance Raman spectra reveal a structural basis for diminished proton and CO2 binding to alpha,alpha-cross-linked hemoglobin.
UV resonance Raman spectra reveal a structural basis for diminished proton and CO2 binding to alpha,alpha-cross-linked hemoglobin.
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DOI：
10.1021/bi981760d
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发表时间：
1999-05
期刊：
影响因子：
2.9
通讯作者：
Lisa A. Dick;G. Heibel;Edwin G. Moore;T. Spiro
中科院分区：
文献类型：
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作者：
Lisa A. Dick;G. Heibel;Edwin G. Moore;T. Spiro
连接血红蛋白和脱氧血红蛋白之间的紫外共振拉曼差异光谱包含色氨酸和酪氨酸信号，这些信号由 T 状态下的四元氢键产生，在 R 状态下断裂。这些氢键不受 Lys α 99 残基处的双（3,5-二溴水杨基）富马酸酯交联的影响，从而防止 Hb 四聚体解离为二聚体。然而，当 pH 从 9.0 降低或添加 NaCl 时，交联脱氧Hb 的酪氨酸 Y8 和色氨酸 W3 条带的强度会减弱，但天然脱氧Hb 的强度不会减弱。这种效应归因于当 Val α 1 和 Arg α 141 之间的 T 态盐桥通过末端氨基的质子化和阴离子结合形成时，涉及 Tyr α 140 和 Trp α 14 的叔氢键减弱。 Tyr α 140-Val α 93 H-键将带有 Arg α 141 的 H 螺旋与带有 Lys α 99 的 G 螺旋连接起来。氢键的减弱反映了富马酸连接基和盐桥之间的张力。这种张力抑制 Val α 1 氨基末端的质子化，从而解释了交联导致 T 态下质子 [玻尔效应] 和 CO2 结合的减少。
UV resonance Raman difference spectra between ligated and deoxyhemoglobin contain tryptophan and tyrosine signals which arise from quaternary H-bonds in the T state, which are broken in the R state. These H-bonds are unaffected by bis(3,5-dibromosalicyl) fumarate cross-linking at the Lys alpha 99 residues, which prevents dissociation of Hb tetramers to dimers. However, when the pH is lowered from 9.0, or when NaCl is added, intensity is diminished for the tyrosine Y8 and tryptophan W3 bands of cross-linked deoxyHb, but not of native deoxyHb. This effect is attributed to weakening of tertiary H-bonds involving Tyr alpha 140 and Trp alpha 14, when the T state salt bridge between Val alpha 1 and Arg alpha 141 is formed via protonation of the terminal amino group and anion binding. The Tyr alpha 140-Val alpha 93 H-bond connects the Arg alpha 141-bearing H helix with the Lys alpha 99-bearing G helix. Weakening of the H-bond reflects a tension between the fumarate linker and the salt-bridge. This tension inhibits protonation of the Val alpha 1 amino terminus, thus accounting for the diminution of both proton [Bohr effect] and CO2 binding in the T state as a result of cross-linking.