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Lanthanides yield versatile protein tags A new class of lanthanide-binding peptide tags for protein labeling should allow for a variety of biochemical applications. Using a well-studied calcium-binding peptide sequence as a starting point, MIT chemistry professor Barbara Imperiali and her coworkers have developed short peptides that bind lanthanide ions with low nanomolar affinity. With the use of standard techniques, a stretch of DNA encoding one of these lanthanide-binding peptides can be fused to any gene of interest, and the peptide-tagged protein can then be expressed and purified. Once loaded with its lanthanide cargo, the tag acts as a fluorescent handle for watching protein-protein interactions. In addition, the X-ray scattering power of the lanthanide ion is sufficient to provide the phasing information necessary for solving protein crystal structures. Plus, protein tags loaded with paramagnetic lanthanide ions such as Ce(III) or Dy(III) can provide long-range distance constraints useful for protein structure determination by NMR spectroscopy, Imperiali tells C&EN. Using a recently obtained X-ray crystal structure of a Tb(III)-loaded tag, her team is now trying to design higher affinity, more intensely fluorescent lanthanide-binding peptide tags |
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