Development of Semisynthesis to Achieve Sulfonium Proteins with Diverse Modifications

Recent advances in sulfonium peptides have demonstrated their potential to study post-translational modifications and protein-protein interactions, owing to the site-selective cross-linking to tryptophan and tyrosine. However, current synthetic methods cannot meet the demand to prepare full-length sulfonium proteins with multiple modifications that mimic cellular scenarios. Here we report a semisynthesis method to address these challenges. We first developed an orthogonal protecting strategy that enables the site-specific incorporation of sulfonium into peptide fragments containing multiple cysteines. After characterization of sulfonium stability in aqueous solutions, the semisynthesis of sulfonium proteins was achieved by native chemical ligation and sortase-mediated ligation. This work expands sulfonium tools to complicated protein levels for diverse biological studies.