SOLUTION X-RAY SCATTERING STUDIES ON PROTEIN INTERACTION

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 生物大分子的溶液X射线散射数据通常既包含由于分子的三维结构而产生的形状因子，也包含反映分子间相互作用的结构因子。在研究蛋白质结构之前，我们将通过为研究中的每一种蛋白质筛选一些不同的溶液条件来表征并最小化后一种影响。许多蛋白质在某些条件下不太容易聚集，例如在盐离子或甘油等惰性化学物质存在的情况下。在这些条件下，辐射诱导的聚集通常也可以被抑制。我们一直在研究溶菌酶在各种条件下的分子间相互作用，旨在建立适用于溶液X射线散射研究的通用方法来预测溶液条件。在模拟中，我们使用包括硬球项、长程排斥静电项和短程吸引势的势项之和，该势项本身包含Van der Waals、疏水、偶极-偶极相互作用以及多极相互作用。正如经验预测的那样，我们已经证实，甘油削弱了溶菌酶分子之间的吸引力相互作用。深入的分析将确定这种变化是由主体溶剂的介电常数改变引起的，这将影响静电势，还是由作用于大分子表面的甘油分子修改的短程疏水作用力引起的。我们还研究了不同盐类的影响，如Cl-和F-，由于相同的净电荷，它们对静电势有相同的影响，而由于不同的离子半径，它们对短程力的影响可能不同。到目前为止，我们的结果表明，在氯化钠存在下，溶菌酶对电位比在氟化钠中更有吸引力。对这一结果的定量解释正在开发中，但NaF可能是在溶液X射线研究中保持蛋白质较少聚集的更好选择。我们将

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Solution x-ray scattering data from biological macromolecules often contain both the form factor, due to the three dimensional structure of the molecule, and the structure factor, which reflects intermolecular interactions. We will characterize and minimize the latter effect by screening a number of different solution conditions, for each protein under study, prior to studying the protein structures. Many proteins are less prone to aggregate under certain conditions, such as in the presence of salt ions or inert chemicals such as glycerol. Radiation induced aggregation can often be suppressed in these conditions as well. We have been studying lysozyme intermolecular interactions in a variety of conditions, aimed at establishing generalized methods to predict solution conditions suitable for solution x-ray scattering studies. We use the sum of potential terms including a hard sphere term, a long-range repulsive electrostatic term, and a short range attractive potential, which itself contains Van der Waals, hydrophobic, dipole-dipole interactions as well as multipole interactions in simulations. As empirically predicted, we have verified that glycerol weakens the attractive interactions among lysozyme molecules. In-depth analysis will determine whether this change is caused by an altered dielectric constant of the bulk solvent, which would influence electrostatic potential, or by modified short-range hydrophobic forces by glycerol molecules acting on the surface of the macromolecules. We also study effects of various salts, such as Cl- and F-, which are expected to have identical effects on electrostatic potentials due to the same net charge while they are likely to have different effects on short range forces due to different ionic radii. Our results so far show that the lysozyme pair-potential is more attractive in the presence of NaCl than NaF. Quantitative interpretation of this result is being developed, but NaF may be a better alternative to keep proteins less aggregating in solution x-ray studies. We will a