title: Using lanthanoid complexes to phase large macromolecular assemblies.
abstract: Lanthanoid ions exhibit extremely large anomalous X-ray scattering at their L(III) absorption edge. They are thus well suited for anomalous diffraction experiments. A novel class of lanthanoid complexes has been developed that combines the physical properties of lanthanoid atoms with functional chemical groups that allow non-covalent binding to proteins. Two structures of large multimeric proteins have already been determined by using such complexes. Here the use of the luminescent europium tris-dipicolinate complex [Eu(DPA)(3)](3-) to solve the low-resolution structure of a 444 kDa homododecameric aminopeptidase, called PhTET1-12s from the archaea Pyrococcus horikoshii, is reported. Surprisingly, considering the low resolution of the data, the experimental electron density map is very well defined. Experimental phases obtained by using the lanthanoid complex lead to maps displaying particular structural features usually observed in higher-resolution maps. Such complexes open a new way for solving the structure of large molecular assemblies, even with low-resolution data.
authors.affiliation: CEA, IBS, F-38054 Grenoble, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Talon
authors.forename: Richard
authors.initials: R
authors.lastname: Kahn
authors.forename: M Asunción
authors.initials: MA
authors.lastname: Durá
authors.forename: Olivier
authors.initials: O
authors.lastname: Maury
authors.forename: Frédéric M D
authors.initials: FM
authors.lastname: Vellieux
authors.forename: Bruno
authors.initials: B
authors.lastname: Franzetti
authors.forename: Eric
authors.initials: E
authors.lastname: Girard
mesh_terms: D000626:Aminopeptidases / Q000737:chemistry*; D019843:Archaeal Proteins / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D046911:Macromolecular Substances; D043902:Pyrococcus horikoshii / Q000201:enzymology; D012542:Scattering, Radiation; D014961:X-Ray Diffraction
chemical_list: D019843:Archaeal Proteins; D056831:Coordination Complexes; D028581:Lanthanoid Series Elements; D046911:Macromolecular Substances; D000626:Aminopeptidases