Preparation of cross-linked peptides with the linker transformed to thiazine and hydrolyzed thiosuccinimide variants.
Cross-linked peptides were dried in a speed-vac, dissolved in 100 mM Tris-HCl buffer, pH=8.0, and incubated at 37oC for 6 hours to transform them into a thiazine and/or hydrolyzed thiosuccinimide forms that correspond to P3-P4 in Figure S2, P1-P3 in Figure S3, P2-P4 in Figure S4, and P1-P2 in Figure 2. All of the transformed forms were purified by rp-HPLC, collected, and analyzed by MALDI-MS, -MS/MS and LC-MS/MS embedded with UVPD (see below).