Plk3 is a protein kinase involved in cell cycle regulation. Researchers identified the specific site on Plk3 where the AX7503 labeling compound binds. This AX7503 labeling site was mapped to a lysine residue in the ATP binding pocket of Plk3's kinase domain, providing a target for developing inhibitors of Plk3 activity.
Identification of AX7503 labeling site on Plk3. A, MS/MS spectrum of the triply charged labeled active site peptide (m/z 1173.7), CYEATDTETGSAYAVK*VIPQSR, of Plk3. The y fragment ions (from y3 to y20) and b fragment ions (from b3 to b11) of the peptides were observed. Fragments y6 (m/z 700), y7 (m/z 951, doubly charged), and y8 (m/z 1000, doubly charged) indicate that the labeling site of the peptide is Lys-16 in the peptide. B, sequence of Plk3 is presented where the peptide identified by LC-MS/MS analysis is indicated in red.