Lanthanide-tagged proteins--an illuminating partnership.

Lanthanide-tagged proteins are valuable for exploiting the unique properties of Ln ions for investigating protein structure, function, and dynamics. Introduction of the Ln into the target is accomplished via chemical modification with synthetic lanthanide-chelating prosthetic groups or by coexpression with peptide-based binding tags. Complexed Ln-tags offer a heavy-atom site for solving the phase problem in X-ray crystallography. In NMR, paramagnetic lanthanide ions induce residual dipolar couplings and pseudo-contact shifts that yield valuable distance constraints for structural analysis. Lanthanide luminescence-based techniques and Ln-tagged proteins are valuable for investigating the functions and dynamics of large proteins and protein complexes and have been applied in vivo. Overall, the reach of Ln-tagged proteins will increase our ability to understand cellular functions on the molecular level.