Unlike the phosphoester bond, formed during the phosphorylation of serine, threonine or tyrosine residues, the phosphoramidate (P-N bond) in phospho-arginine is unstable at low pH (<8), making it difficult to detect with the traditional mass spectrometry protocols.
The systematic name of this enzyme class is Other names in common use include In Gram-positive bacteria, such as Bacillus subtilis, the arginine kinase McsB phosphorylates the arginine residues on incorrectly folded or aggregated proteins to target them for degradation by the bacterial protease ClpC-ClpP (ClpCP).The phospho-arginine (pArg) modification is recognised by the N-terminal domain of ClpC, the protein-unfolding subunit of the ClpCP protease.
Since phosphorylation reverses arginine's charge, the pArg modification has an unfolding effect on the target protein, easing its proteolytic degradation.
Arginine phosphorylation is a dynamic post-translational modification, which can also be reversed by pArg-specific phosphatases, such as the bacterial YwlE.
The pArg-ClpCP mechanism for protein degradation in bacteria is analogous to the eukaryotic ubiquitin-proteasome system.