SOLUTION X-RAY SCATTERING STUDIES ON PROTEIN INTERACTION

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 来自生物大分子的溶液X射线散射数据通常包含由于分子的三维结构引起的形状因子和反映分子间相互作用的结构因子。在研究蛋白质结构之前，我们将针对研究中的每种蛋白质，通过筛选许多不同的溶液条件来表征和最小化后者的影响。许多蛋白质在某些条件下不太容易聚集，例如在盐离子或惰性化学品（如甘油）存在下。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分子间的相互作用，在各种条件下，旨在建立通用的方法来预测溶液的条件适合于解决方案的X-射线散射研究。 我们使用的势项之和，包括硬球项，长程排斥静电项，和短程吸引势，其本身包含货车德瓦尔斯，疏水，偶极-偶极相互作用以及多极相互作用的模拟。正如经验预测，我们已经证实，甘油削弱了溶菌酶分子之间的吸引力的相互作用。深入分析将确定这种变化是由本体溶剂的介电常数改变引起的，这将影响静电势，还是由甘油分子作用于大分子表面的改性短程疏水力引起的。我们还研究了各种盐的影响，如Cl-和F-，这是预期有相同的静电势的影响，由于相同的净电荷，而它们可能有不同的影响，由于不同的离子半径的短程力。到目前为止，我们的研究结果表明，溶菌酶对电位是更有吸引力的NaCl比NaF的存在下。这一结果的定量解释正在开发中，但氟化钠可能是一个更好的替代品，以保持蛋白质较少聚集在溶液X射线研究。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