Quantitative analysis of protein-lipid interactions using tryptophan fluorescence.

The fluorescent properties of the amino acid tryptophan make it a useful tool for fluorometric assays. Because tryptophan fluorescence is remarkably sensitive to the polarity of the environment, it can be used to determine the affinity of tryptophan-containing peptides for phospholipid vesicles of varying compositions. Here, we describe a method for using tryptophan fluorescence to determine the binding affinities of peptides derived from the proteins Raf-1 and KSR-1 to small unilamellar vesicles containing phosphatidic acid. The method can be extrapolated to measure the binding of other tryptophan-containing peptides or proteins to lipid vesicles.