X-RAY CONTRAST VARIATION IN LIPID SUSPENSIONS USING SUCROSE SOLUTION

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。 在X射线溶液散射中，改变溶剂的电子密度以改变X射线对比度的手段相当有限，这主要是由于造影剂对系统的化学影响。因此，该方法并没有像中子散射中的对应方法那样受到欢迎。然而，适用于在脂质囊泡或bicelles重构的膜蛋白的水溶液的方法有可能区分脂质和蛋白质散射强度。有了这种能力的小角溶液散射技术，以确定可溶性蛋白质的形状可以扩展到某些膜蛋白。在BL 4 -2上启动了一个项目，以探索这种方法的可能性。选择蔗糖作为造影剂，因为预期其对脂质的双层结构仅具有微弱影响。从纯脂质bicelles，我们已经表明，只有小的变化，可以观察到的bicelles的横向尺寸高达约30%（w/w）的水相中的蔗糖浓度。因此，可以假设包埋在脂质双胞中的蛋白质不会由于蔗糖的加入而经历其环境的显著变化。我们将在接下来的一系列实验中继续研究造影剂的作用。

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. In x-ray solution scattering, the means to vary the electron density of the solvent in order to change the x-ray contrast are rather limited mainly due to the chemical influence of the contrast agent on the system. As a result the method has not gained as much popularity as its counterpart in neutron scattering. Yet, applied to aqueous solutions of membrane proteins reconstituted in lipid vesicles or bicelles the method has the potential to distinguish between the lipid and the protein scattering intensities. With this ability the technique of small angle solution scattering to determine the shape of soluble proteins could be extended to certain membrane proteins. A project was started on BL4-2 to explore the possibilities of this approach. Sucrose was chosen as a contrast agent as it is expected to have only a weak effect on the bilayer structure of the lipid. Starting with pure lipid bicelles we have shown that only small changes in lateral size of the bicelles can be observed up to a sucrose concentration of about 30% (w/w) in the aqueous phase. Thus one can assume that a protein embedded in the lipid bicelle will not experience significant changes in its environment due to the addition of the sucrose. We will continue to study the effects of contrast agents in the next series of experiments.