FIGURE 6.

BB-4p-PTEN, photo-cross-linking, and mass spectrometry analysis. A, MALDI-TOF MS spectrum of 18-mer synthetic peptide containing tetraphosphorylation (Ser³⁸⁰, Thr³⁸², Thr³⁸³, and Ser³⁸⁵), Bpa at position 392, and a C-terminal biotinylated lysine used for expressed protein ligation. B, isotopic distribution of a 4+ charged cross-linked peptide with the reported mass, m/z, and Δm from Crossfinder. C, high resolution tandem-MS spectrum of the cross-linked peptide. D, PTEN crystal structure (Protein Data Bank code 1D5R) highlighting the site of cross-linking and other important areas shown to be involved in phospho-C-tail binding.