Widespread arginine phosphorylation in human cells–a novel protein PTM revealed by mass spectrometry

Arginine phosphorylation (pArg) is recently discovered as a ubiquitous protein N-phosphorylation in bacteria. However, its prevalence and roles in mammalian cells remain largely unknown due to the lack of established workflow and the inherent lability of phosphoramidate (P–N) bond. Emerging evidences suggest that N-phosphorylation may extensively exist in eu-karyotes and play crucial roles. We report a phosphoproteomic workflow, which allows for the first time revealing the widespread occurrence of pArg in human cells by mass spectrometry. By virtue of this approach, we identified 152 high-confidence pArg sites derived from 118 proteins. Remarkably, the discovered pArg phosphorylation motif and gene ontology hint a possible cellular function of arginine phosphorylation which may regulate the favorability of propeptide convertase substrate. The obtained pArg dataset paves a way for a better understanding of the biological functions of eukaryotic pArg in the future.