A Diketopinic\nReagent for the Reversible Bioconjugation\nto Arginine Residues on Native Antibodies

Arginine is one of the less commonly targeted amino acids\nin protein\nbioconjugation, despite its unique reactivity and abundance on the\nsurface of proteins. In this work, a molecule containing diketopinic\nacid and an azide handle was developed for the chemo-selective bioconjugation\nto arginine. This compound proved to be efficient for bioconjugation\nto IgG1 and IgG4 antibodies, achieving mono- and double-label conversion\nrates of 37–44 and 12–30%, respectively. Mass spectrometry\nanalysis confirmed the antibody modification at two conserved regions.\nThe compound was also applied for the labeling of other proteins such\nas transferrin, BSA, and an EgA1 nanobody. The conjugation was shown\nto be reversible using an <i>o</i>-phenylenediamine-based\nalkaline solution. This novel conjugation method offers precise and\nstable bioconjugation to proteins, enhancing the potential for various\nbiomedical applications.