High Pressure and Conventional Macromolecular Crystallography using Ultra-short Wavelengths. The Case of the Cornell ERL Source
DR. Fourme1, E. Girard1, I. Ascone1, R. Kahn2, A-C Dhaussy3, and M. Mezouar4
1Synchrotron SOLEIL, BP48, Saint Aubin, France
2IBS,
Grenoble, France
3ENSICAEN, Caen, France
4ESRF,
France
The combination of macromolecular crystallography (MX) and pressure perturbation was pioneered nearly 20 years ago using Be cell. This device was used to determine 3D structures of small proteins ([1],[2]). Diamond anvil cell (DAC) extended the pressure domain beyond 200 MPa. It was used first, in combination with a 2nd generation SR source, for compressibility measurements on lysozyme crystals without subsequent data collection [3]. Recent progress [4] include the use of ultra-short wavelength X-rays emitted by in vacuum undulators at a high energy 3rd generation SR source (ESRF). Data collection are performed at room temperature using special sample mounting techniques. The crystal is translated during data collection in order to irradiate successively fresh zones. The quality of diffraction data recorded on the ESRF ID30/ID27 beamlines can meet usual standards [5]. The 3D structures of proteins (monomeric, dimeric and tetrameric) and of a virus have been refined both at atmospheric and at high pressure. Accordingly, high pressure macromolecular crystallography (HPMX) can now be considered as mature.
Beyond classical studies such as the molecular basis of the adaptation of life to extreme conditions, exploring the energy landscape - and accordingly most of the biologically relevant conformational space of the protein (or other macromolecules) - is probably the major interest of combining pressure perturbation with structural methods. Pressure paves the way to trap and study, in solution [6] or in the crystalline state [2, 7], substates and high energy conformers of biological significance. Indeed, prospects are bright [7].
HPMX requires an intense, parallel and tightly collimated (5-50 microns) hard X-ray beam. (wavelength 0.03-0.04 nm). The extremely high brilliance of the ERL source in this wavelength range will be ideally suited for HPMX using either monochromatic or limited-bandpass Laue techniques. For the scientific case of the proposed Cornell ERL source, we underline that what was learnt from HPMX studies could benefit to the whole field of MX. On the one hand, the unusual experimental conditions used for HPMX data collection ensure high data collection efficiency (DCE). This is also valid for conventional (i.e. at atmospheric pressure) MX, with the prospect to acquire routinely data of unprecedented quality [5]. Second, pressure is a way to improve order in pre-existing crystals [8], and this is of general interest for MX.
References:
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5. R. Fourme, E. Girard, R. Kahn, I. Ascone, M. Mezouar, A. C. Dhaussy, T. Lin, and J. E. Johnson; Acta Cryst. D 59, 1914-1922 (2003)
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