Details

Autor(en) / Beteiligte

• van der Woerd, Mark Johannes

Titel

Assessment of protein crystal quality by X-ray diffraction methods

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

1996

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Protein crystal growth is notoriously difficult and its mechanisms are poorly understood. In order to improve the success rate for growing protein crystals, it is necessary to judge crystal quality. A quality descriptor will allow choice of the best crystals for structure determination. With a quality descriptor it will also become possible to link quality to growth conditions, which leads to improvement of the process of protein crystal growth, as well as general knowledge about this process. Crystal quality is traditionally judged based on size and morphology. In this work a quality descriptor is developed, based on X-ray diffraction. X-ray data from protein crystals can be interpreted in various ways, but not all interpretations are equally useful. It is shown that both reflection intensities of individual observations in relation to their $\sigma$-value and estimates of temperature factors are objective methods for data interpretation. Both methods are independent of data set size and contents, given that the data sets are statistically sound. Temperature factor estimates obtained by Wilson plots and $I/\sigma(I)$ curves were successfully compared for data sets obtained from crystals in three different experiments. Significant differences in data quality are shown in the comparison of hen egg white lysozyme crystals grown from standard preparations at pH 4.7, and crystals grown from ultra-pure enzyme preparations at pH 8.2. Some of the differences observed are likely related to crystal growth conditions. The level of purification of the protein and pH are two possible causes for the differences observed. Data quality also differed significantly for lysozyme crystals grown with different temperature profiles, but it is not possible to conclude if this change in quality is caused by the crystal growth conditions, or by other experimental parameters.