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Nature employs post-translational modifications (PTMs) to induce proximity between proteins by engendering new interactions. Furthermore, we find that protein ligands are invariably proximal to a lysine. Inspired by these two observations, we developed group-transfer chimeras (GRCs) that append a moiety-of-interest to the lysine side chain. GRCs employ a protein's ligand and a handle with a transferase-type reactivity to modify the proximal lysine. Contemporary lysine-targeting group-transfer handles were incompatible with GRCs due to their hydrolytic instability, large size, high reactivity, and synthetic incompatibility with diverse ligands. Accordingly, we developed an N-(sulfonyl)-N-(trifluoroethyl)-ethanamide (SuFA) handle that is stable, small, and exhibits tunable reactivity and synthetic compatibility with diverse ligands and proteins. Using GRCs that group-transfer binders of tags (e.g., HaloTag, FKBP) onto proteins overexpressed in cancer cells, we displayed these binders on the surface of the cancer cell. With a universal T cell engager (UniTE) that binds to the displayed ligands and T cells, these GRCs induced proximity between cancer cells and cytotoxic T cells, leading to the latter's activation. We envision the GRC platform to find utility in basic research and biomedicine.