| Polo-like kinases (PLKs) are Ser/Thr protein kinases that play an essential role during the cell cycle. At least four PLKs exist in mammalian cells: PLK1, PLK2, PLK3, and PLK4 (1). PLKs have a highly conserved amino-terminal kinase domain and a relatively divergent carboxy-terminal domain called the Polo-box domain (PBD). Of the four PLKs, PLK1 is the best characterized (2). PLK1 functions as a key regulator of mitotic events by phosphorylating substrate proteins on centrosomes, kinetochores, the mitotic spindle, and the midbody, and is crucial for proper progression through multiple stages of mitosis (2-4). The PBDs of PLK1 function as a phospho-Ser/Thr-binding module, recognizing the optimal recognition sequence motif Ser-(pSer/pThr)-(Pro/X) (5). Binding of phosphopeptides containing the Ser-(pSer/pThr)-(Pro/X) motif by the PBD in PLK1 relieves its inhibitory function on kinase activity (6). Ser-(pSer/pThr)-Pro peptides are phosphorylated by proline-directed kinases such as cyclin dependent kinases (CDKs). These findings imply that priming phosphorylations on substrates or docking proteins by other mitotic kinases such as CDKs may target PLK1 to its substrates and simultaneously activate its kinase activity. Phospho-PLK Binding Motif (ST*P) (D73F6) Rabbit mAb is a useful tool to study PLK1 binding proteins and PLK1 substrates. |
