A new class of lanthanide complexes to obtain high‐phasing‐power heavy‐atom derivatives for macromolecular crystallography

Because of their intense white lines and large values, lanthanide atoms are of great interest for solving structures of biological macromolecules using single‐wavelength anomalous diffraction (SAD) or multiple‐wavelength anomalous diffraction (MAD) methods. In this work, a series of seven gadolinium complexes are described which provide excellent derivatives for anomalous diffraction experiments in bio­logical systems. These highly soluble lanthanide complexes can easily be introduced into protein crystals either by soaking or by co‐crystallization, without significantly affecting the crystallization conditions, by employing highly concentrated complex solutions (≃100 m M ). De novo phasing by the SAD method was carried out with several proteins of known as well as previously unknown structures by employing this new class of heavy‐atom compounds. Diffraction data were collected either with a laboratory source, making use of the high anomalous signal ( = 12 e − ) of gadolinium with Cu  K α radiation, or with synchrotron radiation at the peak of the gadolinium L III absorption edge, which exhibits a strong white line (λ = 1.711 Å, = 28 e − ). Using one of these gadolinium complexes, Gd‐HPDO3A, the structure of a bacterial chimeric ornithine carbamoyl transferase, OTCase3630, a dodecameric protein of 450 kDa, was determined. Employed with the SAD method, these seven complexes could be of particular interest for high‐throughput macromolecular crystallography.