Characterization of fragmented 3-phosphoinsitide-dependent protein kinase-1 (PDK1) by phosphosite-specific antibodies

The 3-phosphoinositide-dependent protein kinase-1 (PDK1) activates a number of protein kinases of the AGC subfamily, including protein kinase B and ribosomal S6 protein kinase by phosphorylating these kinases at the activation-loop. PDK1 activity is regulated by auto-phosphorylation and is further increased by stimulation of cells. PDK1 has been shown to have several phosphorylation sites including 5 serine and 3 tyrosine residues. However, Ser241 and Tyr373/376 are only involved in the regulation of PDK1 activity.

In this study, we found the putative fragments of PDK1 by using anti-Myc and anti-PDK1 antibodies. Furthermore, the existence of four different sizes of PDK1 were confirmed with other phosphosite specific antibodies.

Taken together, the catalytic domain of PDK1 (42 kDa and 37 kDa) is separately existed in the cells and might be important for the regulation of subset of PDK1 substrate. Because the crystal structural studies suggested that PIF-pocket is located at the catalytic domain and plays a critical role on substrate recognition.

These suggested importance and roles of this fragment are needed to be determined. Further study on these fragments of PDK1 will provide new insight on the regulatory mechanism of PDK1 in patho-physiological condition.