Lanthanide Spectral Arsenal

Lanthanide metal ions are gaining in popularity as a means to increase the power of spectroscopy for studying proteins. In the latest example, Karen N. Allen of Boston University, Barbara Imperiali of MIT, and Harald Schwalbe of Johann Wolfgang Goethe University, in Frankfurt, Germany, teamed up to create peptide-based tags that bind two lanthanide ions and can be added easily to proteins (J. Am. Chem. Soc., DOI: 10.1021/ja070480v). Attached to the protein ubiquitin and loaded with Tb³⁺, the tags provided strong luminescence signals for protein detection. When loaded with the paramagnetic lanthanides Tm³⁺ and Eu³⁺, the tags helped to orient ubiquitin proteins for NMR spectroscopy structure determination. In a second paper, the researchers used tags with Tb³⁺ (shown, silver balls = Tb³⁺) to determine the phases of diffracted X-rays to solve ubiquitin's crystal structure (J. Am. Chem. Soc., DOI: 10.1021/ja070481n). The tags could become valuable tools, the researchers say, especially for studying eukaryotic proteins for which existing approaches, such as the incorporation of selenium for X-ray phasing, have proven difficult.