Recent advances in protein powder diffraction studies at ESRF

<aug><au><fnm>Irene</fnm> <snm>Margiolaki</snm></au>,<orf id="a"><cor email="margiolaki@esrf.fr"></cor> <au><fnm>Jonathan </fnm> P. <snm>Wright</snm></au>,<orf id="a"><cor email="wrigh@esrf.fr"></cor> <au><fnm>Andrew</fnm> N. <snm>Fitch</snm></au>,<orf id="a"> <au><fnm>and <au><fnm>Robert B.</fnm> <snm>Von Dreele</snm></au>,^{<orf id="b} b ">

<aff><oid id="a">European Synchrotron Radiation Facility (ESRF), BP220, F38043 Grenoble Cedex 9, <cny>France</cny></aff>, and <aff><oid id="b">Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, <cny>USA</cny></aff></aug>.

Obtaining the atomic structure of large macromolecules like proteins depends on the availability of good quality single crystals. Following the recent reports of crystal structure refinement (Von Dreele, 1999) and solution (Von Dreele, 2000) of some small protein structures from powder diffraction data, the requirement for a single crystal might be relaxed. Since many materials of interest do not readily form single crystals, the availability of the powder technique widens the spectrum of samples which might be characterised crystallographically. Unfortunately, the collapse of three-dimensional reciprocal space into a one-dimensional powder diffraction pattern leads to a catastrophic loss of information. There is not only the usual phase problem, owing to significant peak overlap it is frequently not even possible to determine the intensity of individual Bragg reflections, but only their sum. Nevertheless, powder diffraction data gives a range of complementary information which can be more difficult to obtain from a single crystal. The peak shapes depend on the microstructure of the material, accurate unit cell parameters can easily be determined and the sample generally survives under nastier conditions.

The powder diffraction technique has developed dramatically in the last 20 years, however, the application to macromolecular crystallography remains in its infancy. Initially, we identified turkey egg-white lysozyme (TEWL) as a good candidate material for a trial powder diffraction study for several reasons. Owing to the similarity to hen egg-white lysozyme (HEWL), a great deal is known about the system already, although TEWL will hopefully be more representative of a typical microcrystalline sample in comparison to HEWL, which readily forms large crystals of excellent quality. We would like to know if it is possible to exploit molecular replacement techniques with powder data: the TEWL structure was originally solved in this way. Furthermore, we aim to illustrate the kind of complementary information which can be derived simply from powder data when a sample goes through a catastrophic phase transition. We report refinements of the room temperature crystal structure from powder data, the variation of the unit cell parameters with pH of the precipitation medium and an investigation into the processes occurring when the sample is frozen. Finally, recent results from a series of X-ray powder diffraction experiments in different systems such as insulin, trypsin and conclavin-A will be presented.

Von Dreele, R. B. (1999) J. Appl. Cryst. 32, 1084-1089.

Von Dreele, R. B. (2000) Acta Cryst. D56, 1549-1553.