Fig. 4. Reactive peptides selectively crosslink to MBP-16E6. (A) Crosslinking reaction of MBP–16E6 (1 μM) and reactide 13 (3 μM). Quantitative mono-crosslinked MBP–16E6–13 was observed at 2 h. (B) Crosslinking of MBP–16E6 C58S (1 μM) and peptide 13 (3 μM), no appreciable amount of reaction product was observed after 12 h. (C) Crosslinking of MBP–16E6 (1 μM) and peptide 13-3L3A (3 μM), no appreciable amount of reaction product was observed after 12 h. (D) Protein-selective intermolecular crosslinking of MBP–16E6 in a protein mixture. Only 16E6 was modified, as indicated by the LC-MS analysis. (E) BLI assay determined 16E6/E6AP complex formation. 1 μM of biotin–E6AP protein was immobilized on the streptavidin tip and dipped into 1 μM of MBP–16E6 only (blue), MBP–16E6 mixed with 1 μM of 13 (red) or MBP–16E6 mixed with 1 μM of 13-3L3A (green).