Arginine accelerates sulfur fluoride exchange and phosphorus fluoride exchange reactions between proteins

Sulfur fluoride exchange (SuFEx) and phosphorus fluoride exchange (PFEx) click chemistries are transforming interdisciplinary research. By genetically encoding latent bioreactive unnatural amino acids (Uaas), these chemistries have been successfully integrated into proteins, enabling precise covalent linkages with biomacromolecules. This advancement opens innovative avenues in both fundamental and applied biological research. However, the suboptimal reaction rates of SuFEx and PFEx in proteins pose challenges to their effectiveness in diverse applications. Current catalytic methods for small molecules are largely bioincompatible or unsuitable for in vivo use. We discovered that introducing an arginine adjacent to the latent bioreactive Uaa significantly accelerates both SuFEx and PFEx reaction rates in proteins. This approach effectively improves reaction rates and yields across various Uaas, target residues, and protein contexts. Remarkably, it also enables efficient SuFEx reactions in acidic conditions–environments typically challenging for SuFEx but prevalent in specific cellular compartments and tumor microenvironments. Moreover, we introduce the first covalent cell engager that substantially boosts NK cell activation via enhanced covalent interaction driven by arginine acceleration. These findings offer mechanistic insights and present a viable, biocompatible strategy for exploiting these robust chemistries to advance biological research and develop biotherapeutic interventions.