Wallace B A, Hendrickson W A, Ravikumar K
Department of Chemistry, Rensselaer Polytechnic Institute, Troy, NY 12180.
Acta Crystallogr B. 1990 Jun 1;46 ( Pt 3):440-6. doi: 10.1107/s0108768190001161.
Single-wavelength Cu K alpha anomalous scattering has been used to determine the structure of a crystalline complex of gramicidin A and caesium chloride. The asymmetric unit in these crystals, with space group P2(1)2(1)2(1) and a = 32.118 (6), b = 52.103 (12), c = 31.174 (7) A, contains four independent monomers (two dimers) of the pentadecapeptide. This structure falls in an intermediate size range for which direct methods and multiple isomorphous replacement are generally not successful for obtaining phase information. However, using the Bijvoet differences and the partial structure of the caesium atoms which have been incorporated in the crystals, it has been possible to obtain information on this crystal form. Because the caesium atoms dominate the scattering of these crystals, inclusion of the Friedel mate information in the restrained least-squares refinement has been essential. These studies extend the utility of single-wavelength anomalous-scattering phase determination to a macromolecular structure in which the partial structure of the anomalous scatterer is large.
单波长铜Kα反常散射已被用于确定短杆菌肽A与氯化铯晶体复合物的结构。这些晶体的不对称单元属于空间群P2(1)2(1)2(1)，a = 32.118 (6) Å，b = 52.103 (12) Å，c = 31.174 (7) Å，包含四个独立的十五肽单体（两个二聚体）。这种结构处于中等尺寸范围，对于该尺寸范围，直接法和多重同晶置换通常无法成功获得相位信息。然而，利用拜沃伊特差值以及已掺入晶体中的铯原子的部分结构，得以获取有关这种晶体形式的信息。由于铯原子主导了这些晶体的散射，因此在约束最小二乘精修中纳入弗里德尔对映体信息至关重要。这些研究将单波长反常散射相位测定的应用扩展到了一种大分子结构，其中反常散射体的部分结构较大。
