Snook C F, Wallace B A
Department of Crystallography, Birkbeck College, University of London, London WC1E 7HX, England.
Acta Crystallogr D Biol Crystallogr. 1999 Sep;55(Pt 9):1539-45. doi: 10.1107/s0907444999007921.
The successful use of molecular-replacement methods for the solution of the intermediate-sized helical polypeptide antiamoebin I required the careful consideration of a number of parameters and exhibited some unusual characteristics when compared with molecular-replacement solutions of globular proteins. High-resolution data were required owing to several features, including the comma-like shape of the molecule (which results in a pseudo-symmetric structure at low resolution), the relative uniformity of the structure in the direction along the helix axis and the small differences between the two independent molecules in the P1 asymmetric unit. Other parameters which were important for the solution of this relatively low solvent content closely packed cell included the radius of integration, the use of normalized structure factors and especially the choice of starting model.
要成功运用分子置换法解析中等大小的螺旋多肽抗阿米巴蛋白I，需要仔细考虑多个参数，并且与球状蛋白的分子置换解析结果相比，呈现出一些不同寻常的特征。由于多个因素，包括分子呈逗号状（这在低分辨率下会导致假对称结构）、沿螺旋轴方向结构相对均匀以及P1不对称单元中两个独立分子之间差异较小等，因此需要高分辨率数据。对于这个溶剂含量相对较低、堆积紧密的晶胞的解析，其他重要参数包括积分半径、归一化结构因子的使用，尤其是起始模型的选择。
