Gabel Frank, Engilberge Sylvain, Pérez Javier, Girard Eric
IBS, CEA, CNRS, UGA, 71 avenue des Martyrs, 38000 Grenoble, France.
Synchrotron SOLEIL, Saint-Aubin BP 48, 91192 Gif-sur-Yvette, France.
IUCrJ. 2019 May 29;6(Pt 4):521-525. doi: 10.1107/S2052252519005943. eCollection 2019 Jul 1.
Small-angle X-ray scattering (SAXS) is increasingly used to extract structural information from a multitude of soft-matter and biological systems in aqueous solution, including polymers, detergents, lipids, colloids, proteins and RNA/DNA. When SAXS data are recorded at multiple contrasts, at different electron densities of the solvent, the internal electron-density profile of solubilized molecular systems can be probed. However, contrast-variation SAXS has been limited by the range of electron densities available by conventional agents such as sugars, glycerol and salt, and by the fact that many soft-matter and biological systems are modified in their presence. Here we present a pioneering SAXS contrast-variation study on DDM (-do-decyl-β-d-malto-pyran-oside) micelles by using two highly electron-rich contrast agents from biomedical imaging which belong to the families of gadolinium-based and iodinated molecules. The two agents, Gd-HPDO3A and iohexol, were allowed to attain modifications of the solvent electron density that are 50 to 100% higher than those obtained for sucrose, and are located between the electron densities of proteins and RNA/DNA. In the case of Gd-HPDO3A, an analysis of the internal micellar structure was possible and compared with results obtained with sucrose. In conclusion, medical contrast agents represent a promising class of molecules for SAXS contrast-variation experiments with potential appli-cations for numerous soft-matter and biological systems, including membrane proteins and protein-RNA/DNA complexes.
小角X射线散射（SAXS）越来越多地用于从多种水溶液中的软物质和生物系统中提取结构信息，这些系统包括聚合物、洗涤剂、脂质、胶体、蛋白质以及RNA/DNA。当在不同溶剂电子密度下的多个对比度下记录SAXS数据时，就可以探测溶解分子系统的内部电子密度分布。然而，对比度变化SAXS受到传统试剂（如糖、甘油和盐）可提供的电子密度范围的限制，并且许多软物质和生物系统在其存在的情况下会发生改变。在此，我们通过使用两种来自生物医学成像的高富电子对比度试剂（属于钆基和碘化分子家族），对DDM（十二烷基-β-D-麦芽糖苷）胶束进行了开创性的SAXS对比度变化研究。这两种试剂，钆-羟丙基二乙烯三胺五乙酸（Gd-HPDO3A）和碘海醇，使溶剂电子密度的变化比蔗糖获得的变化高50%至100%，且位于蛋白质与RNA/DNA的电子密度之间。对于Gd-HPDO3A，有可能对胶束内部结构进行分析，并与用蔗糖获得的结果进行比较。总之，医学造影剂代表了一类有前途的分子，可用于SAXS对比度变化实验，对众多软物质和生物系统（包括膜蛋白和蛋白质-RNA/DNA复合物）具有潜在应用价值。
