MS03-P03 Long-wavelength phasing at the P13 EMBL Macromolecular Crystallography beamline at Petra III Guillaume Pompidor (European Molecular Biology Laboratory, Hamburg, Germany) Gleb Bourenkov (European Molecular Biology Laboratory, Hamburg, Germany) Isabel Bento (European Molecular Biology Laboratory, Hamburg, Germany) Johanna Hakanp√§√§ (European Molecular Biology Laboratory, Hamburg, Germany) Ivars Karpics (European Molecular Biology Laboratory, Hamburg, Germany) Thomas Schneider (European Molecular Biology Laboratory, Hamburg, Germany)email: pompidor@embl-hamburg.deThe P13 Macromolecular Crystallography beamline, operated by the EMBL at PETRA III, enables diffraction data collection over a wide energy range, from 4 keV to 17.5 keV (0.7 – 3.1 Å)[1]. In order to fully exploit the beamline capability at low energy (1012 ph.s-1 at 5 keV), the PILATUS 6M-F detector, with a 450 mm Si sensor thickness and with a custom calibration at low energy, is mounted on a 2 q-angle stage to increase the maximum resolution achievable (2.4 Å at 4keV).
We will present and describe the typical experimental setup for long wavelength data collection. For low-energy experiments, typically below 5.5 keV, the air absorption can be drastically reduced by the use of a helium path. The gas is circulating inside the detector and in a homemade cone, which can be fixed on the detector upon user request.
The beamline can be setup for low-energy data collection in about 10 minutes and remains fully compatible with the use of the sample changer, for high-throughput screening, and the mini-k of the MD2 diffractometer allowing the reorientation of the crystal for optimized anomalous data collection.
Several examples of structure determination using intrinsic anomalous scatterers, such as sulfur (SAD) or calcium (MAD at the Ca K-edge at 4.05 keV) will be presented. We will especially demonstrate the efficiency of the He-path in the improvement of diffraction data quality at low energy.
To extend the experimental opportunities, a small laboratory dedicated to the preparation of derivatives is available to users. With more than 150 compounds available, the heavy atom library contains many elements (Cd, Pd, U…) exhibiting strong anomalous signal at low energy, which are excellent candidates for SAD and MAD experiment at long wavelength.

[1] Cianci, M. et al., (2017). Journal of synchrotron radiation 24, 323-332.
Keywords: Long-wavelength phasing