Burling F T, Weis W I, Flaherty K M, Brünger A T
Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA.
Science. 1996 Jan 5;271(5245):72-7. doi: 10.1126/science.271.5245.72.
A complete and accurate set of experimental crystallographic phases to a resolution of 1.8 angstroms was obtained for a 230-residue dimeric fragment of rat mannose-binding protein A with the use of multiwavelength anomalous dispersion (MAD) phasing. An accurate image of the crystal structure could thus be obtained without resort to phases calculated from a model. Partially reduced disulfide bonds, local disorder, and differences in the mobility of chemically equivalent molecules are apparent in the experimental electron density map. A solvation layer is visible that includes well-ordered sites of hydration around polar and charged protein atoms, as well as diffuse, partially disordered solvent shells around exposed hydrophobic groups. Because the experimental phases and the resulting electron density map are free from the influence of a model, they provide a stringent test of theoretical models of macromolecular solvation, motion, and conformational heterogeneity.
利用多波长反常散射（MAD）相位法，获得了大鼠甘露糖结合蛋白A的一个230个残基的二聚体片段分辨率为1.8埃的完整且准确的实验晶体学相位。因此，无需借助从模型计算出的相位，就能获得晶体结构的精确图像。在实验电子密度图中，部分还原的二硫键、局部无序以及化学等价分子迁移率的差异清晰可见。可以看到一个溶剂化层，其中包括围绕极性和带电荷蛋白质原子的有序水合位点，以及围绕暴露疏水基团的弥散、部分无序的溶剂壳。由于实验相位和由此产生的电子密度图不受模型的影响，它们为大分子溶剂化、运动和构象异质性的理论模型提供了严格的检验。
