Validation of PIN1 as the BDHI-reactive protein. (A) Competitive and concentration-dependent inhibition of IA-TAMRA labeling of PIN1 by 18. Recombinant PIN1 was preincubated with each compound (500 μM, 4 h), labeled with IA-TAMRA (1 μM, 1 h), and subsequently analyzed by SDS-PAGE and in-gel fluorescence. (B) Annotated MS2 fragmentation spectra analysis of PIN1 liganded with BDHI 18 at the catalytic active site Cys113, highlighted in red. (C) Docking prediction of 18 binding to PIN1 (PDB: 7EKV). The predicted binding pose of 18 (green) is superimposed with the crystal structure of PIN1 with a covalently bound inhibitor sulfopin (cyan) (PDB: 6VAJ).