Fig. 6: Analysis of the unfolded states of BSA by DOPA2 cross-linking.

a The spectral counts of the inter-molecular cross-link (Lys524-Lys524) are normalized as Z-scores and plotted against urea concentration. This cross-link is marked on the crystal structure of a BSA dimer (PDB code: 3V03⁵¹), with Trp213 represented by purple sticks in one of the subunit. b–f As in (a), but for cross-links of Clusters 1–5. The cross-links are indicated on the structure of the BSA monomer, with Domain I, II, and III in light orange, green, and cyan, respectively. The color of a two lysine residues (highlighted in red) denotes whether or not the indicated cross-link fits within the maximal cross-linking distance of DOPA2 when mapped to the native structure of BSA (black, ≤30.2 Å; red, >30.2 Å). We performed two independent cross-linking experiments for each sample, and each was analyzed twice by LC-MS/MS. Cross-linking residue pairs were filtered by requiring FDR < 0.01 at the spectra level, E-value < 1 × 10⁻⁸ and spectral counts > 3. Source data for (a–f) are provided as a Source Data file.