A Diketopinic Reagent for the Reversible Bioconjugation to Arginine Residues on Native Antibodies.

Arginine is one of the less commonly targeted amino acids in protein bioconjugation, despite its unique reactivity and abundance on the surface of proteins. In this work, a molecule containing diketopinic acid and an azide handle was developed for the chemo-selective bioconjugation to arginine. This compound proved to be efficient for bioconjugation to IgG1 and IgG4 antibodies, achieving mono- and double-label conversion rates of 37-44 and 12-30%, respectively. Mass spectrometry analysis confirmed the antibody modification at two conserved regions. The compound was also applied for the labeling of other proteins such as transferrin, BSA, and an EgA1 nanobody. The conjugation was shown to be reversible using an o-phenylenediamine-based alkaline solution. This novel conjugation method offers precise and stable bioconjugation to proteins, enhancing the potential for various biomedical applications.