The 2.4-A crystal structure of Scapharca dimeric hemoglobin. Cooperativity based on directly communicating hemes at a novel subunit interface.
The 2.4-A crystal structure of Scapharca dimeric hemoglobin. Cooperativity based on directly communicating hemes at a novel subunit interface.
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蚶二聚血红蛋白的 2.4-A 晶体结构。
DOI：
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发表时间：
1991
影响因子：
4.8
通讯作者：
E. Chiancone
中科院分区：
文献类型：
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作者：
W. Royer;W. Hendrickson;E. Chiancone
在碳氧状态下，测定了酸性蛤（Scapharca inaequivalvis）的二聚血红蛋白的晶体结构。利用卟啉铁原子在单波长测量的反常散射，结合分子平均，解决了Bragg间距大于3a的反射的相位问题。建立在电子密度图中的模型已经通过立体化学约束最小二乘最小化来细化到2.4 A分辨率的常规r值0.156。与理想键长和键角的均方根偏差分别为0.013 A和1.7度。除了2336个血红蛋白原子外，该模型还包含214个水分子。这种结构揭示了两个相同的肌红蛋白样亚基的组合的细节，这与脊椎动物的血红蛋白完全不同。亚基界面是由E和F螺旋的直接接触形成的，而这些表面在脊椎动物血红蛋白中是外部的。该界面具有疏水性和亲水性。两个对称相关的疏水区域在亚基之间形成。在这些区域中，每个区域都有六个残基，它们紧密地聚集在一起，足以排除水，但只有少数原子处于紧密的范德华接触中。许多有序的水分子排列在界面上，并在亚基之间形成桥接氢键。形成了四个亚基间离子相互作用，其中两个涉及带负电荷的卟啉丙酸基团。与合作的脊椎动物血红蛋白不同，氢键网络为两个血红素群之间的交流提供了直接途径。
The crystal structure of the cooperative dimeric hemoglobin from the arcid clam, Scapharca inaequivalvis, has been determined in the carbonmonoxy state. The phase problem was solved for reflections with Bragg spacings greater than 3 A using anomalous scattering from the porphyrin iron atoms measured at a single wavelength in combination with molecular averaging. The model built into this electron density map has been refined at 2.4 A resolution by means of stereochemically restrained least squares minimization to a conventional R-value of 0.156. The root mean square deviation from ideal bond lengths and angles are 0.013 A and 1.7 degrees, respectively. In addition to the 2336 hemoglobin atoms, 214 water molecules have been incorporated into the model. This structure reveals the details of an assemblage of two identical myoglobin-like subunits that is radically different from vertebrate hemoglobins. The subunit interface is formed by direct apposition of the E and F helices, whereas these surfaces are external in vertebrate hemoglobins. The interface has both hydrophobic and hydrophilic character. Two symmetrically related hydrophobic regions are formed between subunits. Six residues are involved in each of these regions that pack tightly enough to exclude water but have only a few atoms in close van der Waals contact. A number of ordered water molecules line the interface and form bridging hydrogen bonds between subunits. Four intersubunit ionic interactions are formed, two of which involve negatively charged propionate groups of the porphyrin. In contrast to cooperative vertebrate hemoglobins, a hydrogen bond network provides a direct route for communication between the two heme groups.