Unearthing the unique stability of thiophosphonium-C-terminal cysteine adducts on peptides and proteins

Herein we report a fundamental discovery on the use of tris(dialkylamino)phosphine reagents for peptide and protein modification. We discovered that C-terminal thiophosphonium species, which are uniquely stable, could be selectively and rapidly generated from their disulfide counterparts. In sharp and direct contrast, internal thiophosphonium species rapidly degrade to dehydroalanine. We demonstrate this remarkable chemoselectivity on a bis-cysteine model peptide, and the formation of a stable C-terminal-thiophosphonium adduct on an antibody fragment, as well as characterise the species in various small molecule/peptide studies.

Automated summary

In this study, we report a significant discovery regarding the use of tris(dialkylamino)phosphine reagents in peptide and protein modification. We found that C-terminal thiophosphonium species can be selectively and rapidly generated from their disulfide counterparts, with unique stability. In contrast, internal thiophosphonium species degrade quickly. We demonstrated this chemoselectivity on a model peptide and an antibody fragment, and characterized the species in various small molecule/peptide studies.