Application of a fluorescent lanthanide chelate label on a solid support device for detecting DNA variation with ligation-based assay

Bioconjugation of proteins with a paramagnetic NMR and fluorescent tag

Site-specific labeling of proteins with lanthanide ions offers great opportunities for investigating the structure, function, and dynamics of proteins by virtue of the unique properties of lanthanides. Lanthanide-tagged proteins can be studied by NMR, X-ray, fluorescence, and EPR spectroscopy. However, the rigidity of a lanthanide tag in labeling of proteins plays a key role in the determination of protein structures and interactions. Pseudocontact shift (PCS) and paramagnetic relaxation enhancement (PRE) are valuable long-range structure restraints in structural-biology NMR spectroscopy. Generation of these paramagnetic restraints generally relies on site-specific tagging of the target proteins with paramagnetic species. To avoid nonspecific interaction between the target protein and paramagnetic tag and achieve reliable paramagnetic effects, the rigidity, stability, and size of lanthanide tag is highly important in paramagnetic labeling of proteins. Here 4'-mercapto-2,2':6',2''-terpyridine-6,6''-dicarboxylic acid (4MTDA) is introduced as a a rigid paramagnetic and fluorescent tag which can be site-specifically attached to a protein by formation of a disulfide bond. 4MTDA can be readily immobilized by coordination of the protein side chain to the lanthanide ion. Large PCSs and RDCs were observed for 4MTDA-tagged proteins in complexes with paramagnetic lanthanide ions. At an excitation wavelength of 340 nm, the complex formed by protein-4MTDA and Tb(3+) produces high fluorescence with the main emission at 545 nm. These interesting features of 4MTDA make it a very promising tag that can be exploited in NMR, fluorescence, and EPR spectroscopic studies on protein structure, interaction, and dynamics.

Near IR-emitting DNA-probes exploiting stepwise energy transfer processes

The synthesis and characterisation of two new cyclen-based near IR-emitting lanthanide complexes is reported; the lanthanides are sensitised by rhodamine, which in turn is excited by energy transfer from a coumarin 2 moiety. The three lumophores function as an energy transfer cascade spanning the UV-visible-near IR region of the spectrum, resulting in large Stokes shifts. Double stranded DNA selectively switches one of the two energy transfer processes off, enabling luminescent DNA-sensing in the near IR region. The regioselective di-alkylation of the cyclen scaffold is explained with the help of DFT calculations.