Phosphorylate

Protein phosphorylation

Protein phosphorylation is common on human non-canonical amino acids, including motifs containing phosphorylated histidine, aspartate, glutamate, cysteine, arginine and lysine in HeLa cell extracts. Histidine phosphorylates at both the 1 and 3 N-atoms of the imidazole ring. Phospho-tyrosine is much more stable than phospho-serine and -threonine which are in turn more stable than other phospho-amino acids, hence the analysis of phosphorylated histidine (and other non-canonical amino acids) using standard biochemical and mass spectrometric approaches is much more challenging and special procedures and separation techniques are required for their preservation alongside classical Ser, Thr and Tyr phosphorylation.