Double-Lanthanide-Binding Tags: Design, Photophysical Properties, and NMR Applications

Lanthanide-binding tags (LBTs) are peptide sequences of up to 20 encoded amino acids that tightly and selectively complex lanthanide ions and can sensitize terbium (Tb3+) luminescence. On the basis of these properties, it was predicted that increasing the number of bound lanthanides would improve the capabilities of these tags. Therefore, using a structurally well-characterized single-LBT sequence as a starting point, a “double-LBT” (dLBT), which concatenates two lanthanide-binding motifs, was designed. Herein we report the generation of dLBT peptides and luminescence and NMR studies on a dLBT-tagged ubiquitin fusion protein. These lanthanide-bound constructs are shown to be improved luminescent tags with avid lanthanide binding and up to 3-fold greater luminescence intensity. NMR experiments were conducted on the ubiquitin construct, wherein bound paramagnetic lanthanides were used as alignment-inducing agents to gain residual dipolar couplings, which are valuable restraints for macromolecular structure ...