Structure of a monoclinic polymorph of human carbonic anhydrase II with a doubled a axis.
Structure of a monoclinic polymorph of human carbonic anhydrase II with a doubled a axis.
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DOI：
10.1107/s0907444910006797
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发表时间：
2010-05
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影响因子：
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通讯作者：
A. Robbins;J. Domsic;M. Agbandje-McKenna;R. McKenna
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文献类型：
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作者：
A. Robbins;J. Domsic;M. Agbandje-McKenna;R. McKenna
测定了人碳酸酐酶II的晶体结构，其晶体结构与通常观察到的单斜晶胞的晶体结构成两倍轴，并被细化到1.4A的分辨率。H=2n+1的衍射数据系统地弱于h=2n的数据。因此，数据的规模、结构解决方案和改进都是具有挑战性的。组成不对称单元的两个分子通过(1/2)沿a的非晶学平移联系在一起，但其中一个分子有两个交替的位置，通过大约2度的旋转联系在一起。这个旋转轴位于中心β-折叠的边缘附近，导致分子直径相反一侧的等效原子之间的最大距离差异为1.7A。晶体填充触点类似于沿着先前确定的单斜晶胞之一的两个连续的组合晶胞。异常高的最终R(Cryst)和R(Free)值(分别为20.2%和23.7%)对于包含伪平移对称的结构来说并不罕见，可能是由于弱h奇数数据中的信噪比较低造成的。
The crystal structure of human carbonic anhydrase II with a doubled a axis from that of the usually observed monoclinic unit cell has been determined and refined to 1.4 A resolution. The diffraction data with h = 2n + 1 were systematically weaker than those with h = 2n. Consequently, the scaling of the data, structure solution and refinement were challenging. The two molecules comprising the asymmetric unit are related by a noncrystallographic translation of (1/2) along a, but one of the molecules has two alternate positions related by a rotation of approximately 2 degrees. This rotation axis is located near the edge of the central beta-sheet, causing a maximum distance disparity of 1.7 A between equivalent atoms on the diametrically opposite side of the molecule. The crystal-packing contacts are similar to two sequential combined unit cells along a of the previously determined monoclinic unit cell. Abnormally high final R(cryst) and R(free) values (20.2% and 23.7%, respectively) are not unusual for structures containing pseudo-translational symmetry and probably result from poor signal to noise in the weak h-odd data.