Figure 7.

ERp57 promotes formation of the Cys-370–Cys-371 disulfide bond of TG2. Reduced (active) TG2 and oxidized ERp57 were coincubated in equimolar amounts for 0 or 30 min at 37 °C. Proteins were quenched with IAM to freeze thiol-disulfide exchange and to modify reduced Cys residues (+57 Da). Oxidized Cys residues were identified following reduction with DTT, and labeling with IAA (+58 Da). Following tryptic digest, peptides were subjected to liquid chromatography-mass spectrometry. Modified peptides were validated by their isotopic distribution and y fragment ions (Figs. S2–S5). The extracted ion chromatogram of each modified peptide (Table S1) is presented at 0 min (top) and 30 min (bottom).