Fluorine NMR Spectroscopy Enables to Quantify the Affinity Between DNA and Proteins in Cell Lysate.

The determination of the binding affinity quantifying the interaction between proteins and nucleic acids is of crucial interest in biological and chemical research. Here, we have made use of sitespecific fluorine labeling of the cold shock protein from Bacillus subtiliis , Bs CspB, enabling to directly monitor the interaction with single stranded DNA molecules in cell lysate. High-resolution 19 F NMR spectroscopy has been applied to exclusively report on resonance signals arising from the protein under study. We have found that this experimental approach advances the reliable determination of the binding affinity between single stranded DNA molecules and its target protein in this complex biological environment by intertwining analyses based on NMR chemical shifts, signal heights, line shapes and simulations. We propose that the here developed experimental platform offers a potent approach for the identification of binding affinities characterizing intermolecular interactions in native surroundings covering the nano-to-micromolar range that can be even expanded to in cell applications in future studies.