Mapping preferred sites for fluorescent labeling by combining fluorescence and MS analysis of tryptic CNA35 protein digests

HPLC–MS analysis of tryptic protein digests in combination with fluorescence detection is presented as a convenient and quantitative method to gain insight into the relative reactivity of lysine side chains. In this scheme (tandem) mass spectrometry was used for identification of the modified residue, whereas fluorescence detection allowed determination of their relative abundance. Our method identified ‘labeling hot-spots’ at two flexible parts of the collagen-binding protein CNA35, positions that were consistent with all available structural and biochemical data on the collagen-binding properties of CNA35.