Friedman J M, Scott T W, Stepnoski R A, Ikeda-Saito M, Yonetani T
J Biol Chem. 1983 Sep 10;258(17):10564-72.
Time-resolved Raman studies have shown that communication between the heme oxygen binding sites and the surrounding globin occurs through the iron-proximal histidine linkage. By comparing the frequency of the Fe-His stretching mode in equilibrium deoxy- and photoinduced transient deoxyhemoglobins, we have found that ligand binding induces protein structural changes that strengthen the Fe-His linkage. The extent of this increase is observed to depend upon the quaternary state. This dependence is reflected in the restricted set of values observed in transient and equilibrium studies for the frequency of the Fe-His stretching mode in both R and T state deoxyhemoglobins. For T state hemoglobins the frequency increases from 215 cm-1 to approximately 222 cm-1 in going from the stable to the nanosecond transient deoxy species. The corresponding change for R state human hemoglobins is from approximately 222 cm-1 to approximately 230 cm-1. Studies on transients derived from Fe-Co hybrid hemoglobins reveal no subunit heterogeneity associated with the R state transient (230 cm-1) at high pH. We also observe that perturbations of the protein known to destabilize the structure of ligand-bound R state hemoglobins are associated with a decrease in the frequency of the iron-proximal histidine stretching mode in the corresponding transient species. Such effects can originate from changes in either quaternary state or solution conditions as well as species-specific variations in protein structure. These results indicate that modulation of the Fe-His linkage could be a general mechanism for regulating ligand binding properties in hemoglobin. A direct connection between ligand binding and the Fe-His bond is suggested from our finding that the structural parameter(s) regulating the barrier height for germinate recombination is likely to be the same as the one(s) modulating the frequency of the Fe-His stretching mode in the transient deoxy species. Based on the recent conclusion that the variation in the tilt of histidine with respect to the heme plane is primarily responsible for the spectrum of frequencies observed for the Fe-His stretching mode we have examined a model in which protein regulation of binding occurs via a protein-induced change in the histidine tilt.
时间分辨拉曼研究表明，血红素氧结合位点与周围珠蛋白之间的通讯是通过铁近端组氨酸连接进行的。通过比较平衡脱氧血红蛋白和光诱导瞬态脱氧血红蛋白中铁-组氨酸伸缩模式的频率，我们发现配体结合会诱导蛋白质结构变化，从而加强铁-组氨酸连接。观察到这种增加的程度取决于四级结构状态。这种依赖性反映在R态和T态脱氧血红蛋白中铁-组氨酸伸缩模式频率的瞬态和平衡研究中观察到的有限值集上。对于T态血红蛋白，从稳定的脱氧物种到纳秒瞬态脱氧物种，频率从215厘米-1增加到约222厘米-1。R态人血红蛋白的相应变化是从约222厘米-1到约230厘米-1。对铁-钴杂合血红蛋白产生的瞬态的研究表明，在高pH值下，与R态瞬态（230厘米-1）没有亚基异质性。我们还观察到，已知会破坏配体结合的R态血红蛋白结构稳定性的蛋白质扰动与相应瞬态物种中铁近端组氨酸伸缩模式频率的降低有关。这种影响可能源于四级结构状态或溶液条件的变化以及蛋白质结构的物种特异性变化。这些结果表明，铁-组氨酸连接的调节可能是调节血红蛋白中配体结合特性的一般机制。我们发现调节发芽重组势垒高度的结构参数可能与调节瞬态脱氧物种中铁-组氨酸伸缩模式频率的参数相同，这表明配体结合与铁-组氨酸键之间存在直接联系。基于最近的结论，即组氨酸相对于血红素平面倾斜度的变化主要负责观察到的铁-组氨酸伸缩模式频率谱，我们研究了一种模型，其中蛋白质通过诱导组氨酸倾斜度的变化来调节结合。
