Ub photoLeu73 (UbiQ-154) is a new crosslinking reagent based on ubiquitin in which Leu73 is replaced by the photoreactive analog photoleucine (photoLeu, Figure 1) (1). Upon irradiation of the diazirine with UV light, a very reactive carbene species is formed. Because carbenes are quenched quickly by water, unspecific binding is minimal for carbene based crosslinking. This means that only residues that are very nearby (and contribute to tight binding) will react covalently. Thus any unbound UbiQ-154 will react with water before being able to undergo non-specific reactions with other proteins.

Figure 1

Literature: (1) Chojnacki et al. Cell Chem Biol 2017, 24, 443.