Figure 1.

A) Structure of 1. Su: succinimidyl. B) Workflow for XL‐MS experiments. After the addition of 1, protein sites in close proximity are covalently linked. The generated crosslinks can be functionalised with a copper‐catalysed Huisgen reaction (CuAAC). Excess reagents are removed by acetone precipitations. After enzymatic digestion and enrichment on magnetic streptavidin beads, crosslinked peptides were cleaved off under mild conditions and subsequently analysed by means of LC‐MS². C) Fragmentation pathways of the crosslinked peptides, forming two peptide pairs with a characteristic Δm _rep of 31.9721 u.