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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >On the direct determination of three-dimensional crystallographic phases at low resolution: Crymbin 6 A
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On the direct determination of three-dimensional crystallographic phases at low resolution: Crymbin 6 A

机译：在低分辨率下直接确定三维结晶相：Crymbin 6 A

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摘要

Using a pseudo-atom approach, the three-dimensional crystallo- graphic phases for the protein crambin (a = 40.76, b = 18.49, c = 22.33 A, p = 90.61", space group P21) were determined to 6 A by direct methods. First the centrosymmetric hot set was assigned phases by symbolic addition. and the initial solution was then refined by Fourier methods. Phase values of strong reflections were then permuted, and the decision to change the phase value for two of these was made by consulting a cross-correlation of the experimental density histogram to the theoretical or known his- togram for the protein. The two-dimensional basis was then extended by the Sayre equation into three dimensions by assign- ing a phase to a third allowed hkl origin-defining reflection and an algebraic value to another axial reflection. The correct solution was again identified by the histogram correlation, yielding a solution in which the mean phase error for all 98 reflections was 61 .5' or 23.1 o for the 21 most intense reflections. A parallel study with another protein indicates this method may have general utility.
机译：使用伪原子方法，通过直接方法将蛋白质crambin的三维结晶相（a = 40.76，b = 18.49，c = 22.33 A，p = 90.61“，空间群P21）确定为6 A首先通过符号加法将中心对称热集分配给相位，然后通过傅立叶方法细化初始解，然后对强反射的相位值进行置换，并通过咨询一个决定改变其中两个的相位值。实验密度直方图与蛋白质的理论或已知直方图互相关，然后通过Sayre方程将二维分配给第三个允许的hkl原点定义反射，从而将二维基础扩展为三维直方图相关性再次确定了正确的解，得出了这样一个解，其中对于所有98个反射，所有98个反射的平均相位误差为61 .5'或23.1 o。自我思考。与另一种蛋白质的平行研究表明，该方法可能具有通用性。

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