Scientists from the IQFR and Univ. Complutense of Madrid have synthesized and characterized the first phasing agent designed for solving protein structures at the maximum intensity of the synchrotron facilities.

As a proof of principle, the complex allows determining the 3D structure of a 36 kDa protein without setting the incident beam wavelength at the metal absorption edge, the strategy followed to date to gain the strongest anomalous signal even at the expense of crystallographic resolution. The agent becomes non-disruptive to the diffraction quality of the marked crystals and allows determining accurate phases, both leading to high-quality electron density maps that enable the full tracing of the protein structure only with one agent unit bound to the protein. The high-phasing power, efficient binding to the protein, low metalmacromolecule ratio, and easy handling support the developed Yb (III) complex as the best phasing agent for X-ray crystallography of a complex biomacromolecule without using modified analogues.