Engineering topics
Borgstahl, Gloria E.
Publications and source records attributed to Borgstahl, Gloria E..
Macromolecule Crystal Quality Improvement in Microgravity: The Role of Impurities
While macromolecule impurities may affect crystal size and morphology the over-riding question is; "How do macromolecule impurities effect crystal X-ray quality and diffraction resolution?" In the case of chicken egg white lysozyme, crystals can be grown in the presence of a number of impurities without affecting diffraction resolution. One impurity however, the lysozyme dimer, does negatively impact the X-ray crystal properties. Crystal quality improvement as a result of better partitioning of this impurity during crystallization in microgravity has been reported'. In our recent experimental work dimer partitioning was found to be not significantly different between the two environments. Mosaicity analysis of pure crystals showed a reduced mosaicity and increased signal to noise for the microgravity grown crystals. Dimer incorporation however, did greatly reduce the resolution limit in both ground and microgravity grown crystals. These results indicate that impurity effects in microgravity are complex and may rely on the conditions or techniques employed.
The Question of Impurities in Macromolecule Crystal Quality Improvement in Microgravity
While macromolecule impurities may affect crystal size and morphology the over-riding question is how do macromolecule impurities effect crystal X-ray quality and diffraction resolution. In the case of chicken egg white lysozyme previous researchers have reported that crystals grown in the presence of ovalbumin, ovotransferrin, and turkey egg white lysozyme show no difference in diffraction resolution compared to those grown in pure solutions. One impurity however, a naturally occurring lysozyme dimer, does negatively impact the X-ray crystal properties. For this impurity it has been reported that crystal quality improvement in microgravity may be due to improved impurity partitioning during crystallization. In this study we have examined the incorporation of the dimer into lysozyme crystals, both on the ground and in microgravity experiments, and have performed detailed X-ray analysis of the crystals using a new technique for finely probing the mosaicity of the crystal at the Stanford Synchrotron Radiation Laboratory. Dimer partitioning was not significantly different in microgravity compared to the ground based experiments, although it is significantly better than that previously reported in microgravity. Mosaicity analysis of pure crystals, 1422 indexed reflections (microgravity) and 752 indexed reflections (ground), gave average results of 0.0066 and 0.0092 degrees (FWHM) respectively. The microgravity crystals also provided an increased signal to noise. Dimer incorporation increased the average mosaicity in microgravity but not on the ground. However, dimer incorporation did greatly reduce the resolution limit in both ground and microgravity grown crystals. The data is being treated anisotropically to explore these effects. These results indicate that impurity effects in microgravity are complex and that the conditions or techniques employed may greatly affect the role of impurities.