Carbene Footprinting Accurately Maps Binding Sites in Protein-Ligand and Protein-Protein Interactions

Specific interactions between proteins and their binding partners are fundamental to life processes. Differential protein footprinting using a new and efficient, photo-activated aryltrifluromethylcarbene probe together with mass spectrometry has been employed to identify protein-ligand and protein-protein interaction sites. In a model protein-small molecule system, the location of a penta-N-acetylchitopentaose carbohydrate substrate was accurately mapped to the binding cleft of lysozyme. As a fine detail, footprinting revealed disruption of an intramolecular hydrogen-bond network within lysozyme, which is known to be associated with substrate binding. In a more complex example, the interactions between a 100 kDa, multi-domain deubiquitinating enzyme, USP5, and a diubiquitin substrate were located to different functional domains thus clarifying uncertainties from an X-ray crystal structure of USP5. The much improved properties of this bespoke diazirine probe make differential carbene footprinting a viable method for rapid and accurate identification of protein binding sites utilizing benign, near-UV photoactivation.