ID23-2: Gemini - Macromolecular Crystallography
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Synopsis
Beamline ID23 is part of the Macromolecular Crystallography Group which supports the study and structure determination of biological macromolecules. The beamline is composed of two independent end-stations. ID23-1 is a fully tunable beamline capable of MAD measurements from 6 to 20 keV energy (2.07 Å to 0.62 Å). The second station, ID23-2, is fixed energy (14.20 keV, 0.873 Å) and is dedicated to perform experiments with very small protein crystals. The optical design of ID23-2 makes use of a horizontally diffracting Si (111) monochromator and Pt coated mirrors in a Kirkpatrick-Baez (KB) geometry as the focusing system.
The X-ray sources for the two stations are canted (separated by 1.5mrad of angle) undulators mounted on a special carriage on the storage ring. The ID23-1 undulator is a U35 (allowing tuning of the energy across harmonics) and for ID23-2 a U20.2 is used which is a pseudo-monochromatic source with a single first harmonic at 14.2keV.
EMBL have provided a scientist position to operate the ID23-2 beamline.
Scientific Applications
Protein crystal samples are becoming ever smaller, with today's samples typically around 50 to 100 microns in size. With the development of third generation synchrotron radiation sources, it is now possible to have access to a focused and very intense hard X-ray beam in the µm-range. ID23-2, which produces a focused beam of less than 10 µm in diameter (FWHM) to allow to probe protein microcrystals, is the first microfocusing beamline fully dedicated to macromolecular crystallography.
Bibliography
Interesting papers to be read:
Small is beautiful: protein micro-crystallography ; Cusack S, Belrhali H, Bram A, et al. NATURE STRUCTURAL BIOLOGY 5: 634-637 Suppl. S AUG 1998
Protein microcrystals and the design of a microdiffractometer: current experience and plans at EMBL and ESRF/ID13 ; Perrakis A, Cipriani F, Castagna JC, et al. ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY 55: 1765-1770 Part 10 OCT 1999
The ID23-2 structural biology microfocus beamline at the ESRF, David Flot et al., J Synchrotron Radiat. 2010 January 1; 17(Pt 1): 107–118.
Techniques Available
Microfocus beam, fixed wavelength rapid data collection and SAD/MIR.
Warning
When coming on ID23-2, as a user, you will have to deal with a small and intense beam. Keeping a a 2000 µm3 (about 20 x 10 x 10 µm3) crystal in a 10 µm diameter beam needs good beam stability AND accurate crystal centring.
Crystal centering can be long and difficult. It is important to mount the crystals with a minimum of cryoprotectant. The use of 10 µm diameter nylon loop, lytholoop or mesh loops can allow a better crystal visualisation which will make easier (or just less difficult...) the crystal centering.
Beam drifts
In normal operating conditions, small beam drifts (variations in position of less than 10 µm in both vertically and horizontally directions) have been regularly observed over a period of 12 hours. Such variations are expected and are mainly driven by experimental hutch temperature variations. This kind of small drift does not affect data quality as a typical data collection is less than 15 mn. In the past, in certain conditions, larger beam movements (in the range of 50 µm over half an hour) have been observed (mainly after a "Beam Realign" procedure) but should not anymore exist.
The possibility of beam drift makes regular beam position checks necessary. This can be done either with a pop-up scintillator or a scintillator mounted on the Phi axis as a sample. The second option gives a more accurate result as it possible to move the scintillator to the camera focus.
Contact
Tel: +33 (0)4 76 88 +ext
ID23-2 Control Cabin: 25 90
Beamline responsible: Sean McSWEENEY , 23 62
Scientist in charge: Max NANAO, 33 (0)4 76 20 75 37
Beamline Engineer: Muriel Mattenet, 23 31