Design and synthesis of cysteine-specific labels for photo-crosslinking studies

Chemical cross-linking mass-spectrometry (XL-MS) represents a powerful methodology to map ligand/biomacromolecule interactions, particularly where conventional methods such as X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy or cryo-electron microscopy (EM) are not feasible. In this manuscript, we describe the design and synthesis of two new photo-crosslinking reagents that can be used to specifically label free thiols through either maleimido or methanethiosulfonate groups and facilitate PXL-MS workflows. Both crosslinkers are based on light sensitive diazirines - precursors of highly reactive carbenes which offer additional advantages over alternative crosslinking groups such as benzophenones and aryl nitrenes given the controlled rapid and more indiscriminate reactivity.