Chair of Session 7
Professor Bruce Doak, Max-Planck-Institut fur Medizinische Forschung, Germany and Arizona State University, USA
Liquid jet injectors for X-ray lasers
Dr Uwe Weierstall, Arizona State University, USA
The emerging method of serial femtosecond crystallography (SFX), which uses ultrashort X-ray pulses from an X-ray free electron laser to outrun radiation damage, has been shown recently to achieve atomic resolution from protein microcrystals. An essential requirement for SFX is a sample delivery method, which can keep up with the repetition rate of the XFEL and provides fresh sample for every X-ray pulse. A liquid jet injector has been developed at ASU for this purpose and allows data collection from hydrated biomolecules and microcrystals at room temperature. In order to use protein microcrystals grown in Lipidic cubic phase (LCP) for SFX experiments, a new approach was needed to generate a stream of the gel-like LCP with tens of micrometer diameter. Therefore a new LCP injector has been developed, which allows the collection of data from a contiguous stream of nanocrystals embedded in LCP. An overview of the current injection devices and recent results will be presented.
Daniel James, Dingjie Wang, John C H Spence, R B Doak, Petra Fromme, Arizona State University, USA
Martin Caffrey, Trinity College Dublin, Republic of Ireland
Vadim Cherezov, The Scripps Research Institute, USA
SFX vs PX: comparing crystallographic data from FELs and synchrotrons
Dr Thomas Barends, Max-Planck-Institut fur Medizinische Forschung, Germany
Free-electron lasers (FELs) are pushing back the limits of possibility in protein crystallography. The high-intensity, femtosecond duration pulses afforded by FELs allow data collection from micrometer-sized crystals while outrunning radiation damage. Moreover, FELs may be used for pump-probe experiments with unprecedented time resolution.
However, the intricacies of FEL data collection pose specific challenges: as every FEL pulse destroys the sample, data are mostly collected from a stream of microcrystals and averaged to remove the variations in crystal size and quality as well as shot-to-shot variations in beam parameters. This technique, dubbed serial femtosecond crystallography (SFX) requires specific data processing methods.
Alternatively, data may be collected from a single crystal using an attenuated beam. This, too, requires special processing methods because of the limited sampling of reciprocal space possible in the short duration of the FEL pulse.
We will compare FEL data collected using both methods with comparable data collected using classical methods at synchrotrons, to explore the determinants of data quality in terms of beam and crystal properties.