High-phasing-power lanthanide derivatives: taking advantage of ytterbium and lutetium for optimized anomalous diffraction experiments using synchrotron radiation

Ytterbium and lutetium are well suited for optimized anomalous diffraction experiments using synchrotron radiation. Therefore, two lanthanide complexes Yb-HPDO3A and Lu-­HPDO3A have been produced that are similar to the Gd-HPDO3A complex already known to give good derivative crystals. Derivative crystals of hen egg-white lysozyme were obtained by co-crystallization using 100 mM solutions of each lanthanide complex. De novo phasing has been carried out using single-wavelength anomalous diffraction on data sets collected on each derivative crystal at the L_III absorption edge of the corresponding lanthanide ( = 28 e⁻). A third data set was collected on a Lu-HPDO3A derivative crystal at the Se K absorption edge with = 10 e⁻. The structures were refined and compared with the known structure of the Gd-HPDO3A lysozyme derivative. The quality of the experimental electron-density maps allows easy model building. With L_III absorption edges at shorter wavelengths than the gadolinium absorption edge, lutetium and ytterbium, when chelated by a ligand such as HPDO3A, form lanthanide complexes that are especially interesting for synchrotron-radiation experiments in structural biology.