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

Arginine phosphorylation(p Arg)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 eukaryotes and play crucial roles.We report a phosphoproteomic workflow,which allows for the first time revealing the widespread occurrence of p Arg in human cells by mass spectrometry.By virtue of this approach,we identified 152 high-confidence p Arg sites derived from 118 proteins.Remarkably,the discovered p Arg phosphorylation motif and gene ontology hint a possible cellular function of arginine phosphorylation which may regulate the favorability of propeptide convertase substrate.The obtained p Arg dataset paves a way for a better understanding of the biological functions of eukaryotic p Arg in the future.