Higher Energy Beamlines, a New Paradigm for Macromolecular
Higher Energy Beamlines, a New Paradigm for
Roger Fourme1, Eric Girard2, Richard Kahn2
Synchrotron Soleil, 2IBS Grenoble France
Nearly all macromolecular crystallography (MX) beamlines are optimised for ~1Å
wavelength (photon energy ~12.4 keV). We have routinely used since a decade much
shorter wavelengths (down to ~0.33Å ) for high-pressure macromolecular crystallography
(HPMX)[1,2]. For HPMX data collection on CpMV crystals, we found that DCE (Data
Collection Efficiency, defined as the amount of diffraction data that could be collected per
crystal unit-volume) was increased by the use of a highly monochromatic and parallel
beam of ultra-short wavelength.
The successful use of ultra-short wavelenghs for HPMX led us to investigate the interest of
wavelengths shorter than usual for conventional MX (i.e. at atmospheric pressure). Data
sets were repeatedly collected at the same resolution on a cryo-cooled hen egg-white
lysozyme crystal using 18 and 33 keV photons and a standard CCD detector. The sample
degradation was monitored by the evolution of the average temperature factor as a
function of data set number. With an ideal detector, i.e. with a unit DQE (detective
quantum efficiency), DCE would be approximately x 3 from 18 to 33 keV. Analysis along
the same lines of published data allowed us to extend and consolidate these
conclusions in the range from 6.5 to 33 keV.
It was already admitted that shorter wavelengths paved the way to get data sets of
unprecedented quality, by reducing random and systematic errors. Our results show
that, in addition, DCE is increased by large amounts. On this basis, we have suggested
to build beamlines optimised for very accurate data collection and anomalous phasing in a
broad range of wavelengths (from conventional to ultra-short wavelengths), for both HPMX
and standard MX. As the advantage of going to shorter wavelengths is partly cancelled by
the decreased efficiency of common area detectors (CCD or Si hybrid pixel detectors), the
use of detectors preserving a good DQE even at short wavelengths (e.g by direct
conversion of photons in a Se layer or replacing Si by CdTe in pixel detectors) is crucially
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