Three-dimensional fourier synthesis of human deoxyhaemoglobin at 2-5 A resolution: refinement of the atomic model.
Three-dimensional fourier synthesis of human deoxyhaemoglobin at 2-5 A resolution: refinement of the atomic model.
复制标题
2-5 A 分辨率下人体脱氧血红蛋白的三维傅里叶合成：原子模型的细化。
DOI：
10.1016/s0022-2836(75)80037-4
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发表时间：
1975
影响因子：
5.6
通讯作者：
G. Fermi
中科院分区：
文献类型：
--
作者：
G. Fermi
人类脱氧血红蛋白的结构已经通过将原子坐标拟合到分辨率为2.5 μ m的多同晶置换电子密度图（Ten Eyck & Arnone，1975）而得到了改进;得到的R因子为28.8%。随后的一个傅立叶细化周期将R因子降低到27.6%。用两种独立的方法估算的原子位置的均方根误差，对所有原子来说都是0·40 μ m。所有α碳的估计位置误差为0·30 Å，内部片段的α碳的估计位置误差为0·23 Å，铁的估计位置误差为0·10 Å。铁原子与卟啉平面的距离在α血红素中为0·60 π，在β血红素中为0·63 π;铁连接的组氨酸的N（π）与卟啉平面的距离在α血红素中为2·6 π，在β血红素中为2·8 π。这些距离假定为平面卟啉;分辨率不足以区分平面构象和圆顶构象，铁从卟啉氮平面的位移较小。ValE 11的C（γ）与配体位点的距离在α血红素中为3.4 μ m，在β血红素中为1.8 μ m，因此β血红素中的配体位点被封闭。在本结构中发现Arg FG 4（92）α 1和Glu CD 2（43）β 2之间可能存在盐桥;由于该盐桥不能在血红蛋白切萨皮克中形成（Arg FG 4 α→Leu），因此可能通过其对氧和脱氧四级结构之间平衡的影响来解释突变体的较高氧亲和力（吉布森&内格尔，1974）。人和马脱氧血红蛋白的结构比较表明，仅在β链的氨基末端和A螺旋区域存在显著差异：在两种结构中，A螺旋的质心位置相差1·3 π，氨基末端缬氨酸残基的质心位置相差4 - 5 π，人的A和E螺旋之间的分离大于马的脱氧血红蛋白。
The structure of human deoxyhaemoglobin has been refined by fitting atomic co-ordinates to a multiple-isomorphous replacement electron-density map of 2·5 Å resolution (Ten Eyck & Arnone, 1975); anR-factor of 28·8% was obtained. A subsequent single cycle of Fourier refinement reduced theR-factor to 27·6%. The root-mean-square error in atomic positions, estimated by two independent methods, is 0·40 Å for all atoms. The estimated positional error for all alpha carbons is 0·30 Å, for alpha carbons of internal segments it is 0·23 Å, and for the iron it is 0·10 Å. The distance of the iron atom from the porphyrin plane is 0·60 Å in the α haem and 0·63 Å in theβhaem; the distance of the N(ɛ)of the iron-linked histidine from the porphyrin plane is 2·6 Å in the α haem and 2·8 Å in theβhaem. These distances assume a planar porphyrin; the resolution is insufficient to distinguish between a planar conformation and a domed one, with a lesser displacement of the iron from the plane of the porphyrin nitrogens. The distance of C(γ)of ValE11 from the ligand site is 3·4 Å in the α haem and 1·8 Å in theβhaem, so that the ligand site in theβhaem is blocked. A probable salt bridge between Arg FG4(92)α1and Glu CD2(43)β2is found in the present structure; as this salt bridge cannot be formed in haemoglobin Chesapeake (Arg FG4α→Leu) it may account for the higher oxygen affinity of the mutant (Gibson & Nagel, 1974) through its effect on the equilibrium between the oxy and deoxy quaternary structures. Comparison of the structures of human and horse deoxyhaemoglobin indicates that significant differences occur only in the region of the amino terminus and the A helix of theβchain: the positions of the centres of mass of the A helices differ by 1·3 Å and those of the amino terminal valine residue by 4 to 5 Å in the two structures, the separation between the A and E helices being greater in human than in horse deoxyhaemoglobin.