Molecular Tools for the Study of ADP‐Ribosylation: A Unified and Versatile Method to Synthesise Native Mono‐ADP‐Ribosylated Peptides

ADP‐ribosylation (ADPr), as a post‐translational modification, plays a crucial role in DNA‐repair, immunity and many other cellular and physiological processes. Serine is the main acceptor for ADPr in DNA damage response, whereas the physiological impact of less common ADPr‐modifications of cysteine and threonine side chains is less clear. Generally, gaining molecular insights into ADPr recognition and turn‐over is hampered by the availability of homogeneous, ADP‐ribosylated material, such as mono‐ADP‐ribosylated (MARylated) peptides. Here, a new and efficient solid‐phase strategy for the synthesis of Ser‐, Thr‐ and Cys‐MARylated peptides is described. ADP‐ribosylated cysteine, apart from being a native post‐translational modification in its own right, proved to be suitable as a stabile bioisostere for ADP‐ribosylated serine making it a useful tool to further biochemical research on serine ADP‐ribosylation. In addition, it was discovered that the Streptococcus pyogenes encoded protein, SpyMacroD, acts as a Cys‐(ADP‐ribosyl) hydrolase.