Protein Crystallography at Ultra-Short Wavelengths: Feasibility Study of Anomalous-Dispersion Experiments at the Xenon K-edge

A protein crystallography experiment at the xenon K-edge (λ = 0.358 Å) has been successfully carried out at the materials science beamline (BL2/ID11) of the ESRF. The samples used in this methodological study were crystals of porcine pancreatic elastase, a 26 kDa protein of known structure. The diffraction data are of excellent quality. The combination of isomorphous replacement and anomalous dispersion of a single xenon heavy-atom derivative allowed accurate phase determination and the computation of a high-quality electron density map of the protein molecule. This is the first fully documented report on a complete protein crystallography experiment, from data collection up to phase determination and calculation of an electron density map, carried out with data obtained at ultra-short wavelengths. Experimental considerations as well as possible advantages and drawbacks of protein crystallography at very short and ultra-short wavelengths are discussed.