FEL MS 3P 3 FIP-BM 30 A at the ESRF : an automated beamline for protein crystallography with unique features

Membrane proteins are involved in a number of crucial and diverse biological functions ranging from cross-membrane transportation to signal reception. The structural characterization of these macromolecules is hindered by the difficulty in producing well diffracting three-dimensional crystals, limiting the range of application of conventional X-ray crystallography in these systems. Membrane proteins arrange favorably in periodic monolayers in a lipidic environment. This configuration presents the advantage that molecules are found in a close-to-physiological arrangement. In addition, the use of ultrashort free electron laser (FEL) X-ray pulses allows to largely outrun radiation damage phenomena in biological samples at ambient temperature. Two-dimensional (2D) protein crystals of bacteriorhodopsin proved to give rise to diffraction spots to resolution of 4Å at the Linac Coherent Light Source FEL, where the variable geometrical configuration of the experiment opens up to the possibility of collecting diffraction intensities along reciprocal space Bragg rods (B. Pedrini et al., Phil. Trans. R. Soc. B 369, 2014). The main bottleneck resides to date in 2D data processing and reduction due to the absence of dedicated software in conventional X-ray crystallography software suites. The most recent advancements in 2D crystallography data treatment will be presented with particular focus on the opportunities and challenges of using intensities collected along reciprocal space rods.