Analyzing interactions between SSB and proteins by the use of fluorescence anisotropy

Fluorescence anisotropy is a useful tool to detect SSB interaction with SSB binding partners. Titrating an SSB protein partner into a solution containing fluorescently labeled SSB C-terminal tail (SSB-Ct) peptide results in formation of the protein complex with molecular weights greatly higher than SSB peptide alone. Thus the tumbling of the complexes in solution is slower, and the fluorescence anisotropy (FA) signal would be increased, indicating the binding. Based on the FA binding curve, the apparent dissociation constant (K(d,app)) of the binding reaction can also be calculated.