Structure determination by multiple-wavelength anomalous dispersion (MAD) at the Pr LIII edge.

The use of longer X-ray wavelengths in macromolecular crystallography has grown significantly over the past few years. The main reason for this increased use of longer wavelengths has been to utilize the anomalous signal from sulfur, providing a means for the experimental phasing of native proteins. Here, another possible application of longer X-ray wavelengths is presented: MAD at the L(III) edges of various lanthanide compounds. A first experiment at the L(III) edge of Pr was conducted on HZB MX beamline BL14.2 and resulted in the successful structure determination of the C-terminal domain of a spliceosomal protein. This experiment demonstrates that L(III) edges of lanthanides constitute potentially attractive targets for long-wavelength MAD experiments.