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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 the phosphoramidate (P-N) bond. Emerging evidence suggests that N-phosphorylation may extensively exist in eukaryotes and play crucial roles. We report an experimental phosphoproteomic workflow, which for the first time allowed to reveal the widespread occurrence of pArg in human cells by mass spectrometry. By virtue of this approach, we identified 152 high-confidence pArg sit]es derived from 118 proteins. Remarkably, the discovered phosphorylation motif and gene ontology of pArg hint a possible cellular function of arginine phosphorylation by regulating the favorability of propeptide convertase substrate. The generated extensive data set should enable a better understanding of the biological functions of eukaryotic pArg in the future.