Mapping proximity within proteins using fluorescence spectroscopy. A study of T4 lysozyme showing that tryptophan residues quench bimane fluorescence

We present a novel method for mapping proximity within proteins. The method exploits the quenching of the fluorescent label bimane by nearby Trp residues. In studies of T4 lysozyme we show that this effect appears to be distance dependent and orientation specific. Specifically, we show that a proximal Trp residue can reduce bimane fluorescence intensity by up to 500% and induce complicated fluorescence decay kinetics. Replacing the neighboring Trp residue with phenylalanine removes these spectral perturbations. The advantages of using the Tip quenching of bimane fluorescence for protein structural studies include the low amount of protein required and the substantial simplification of labeling strategies. We anticipate this method will prove suitable for a wide array of high-throughput protein studies such as protein folding, the detection of protein-protein interactions, and, most importantly, the dynamic monitoring of conformational changes.