In the field of biochemistry, 3-phosphoinositide dependent protein kinase-1, also known as PDPK1 is a protein which in humans is encoded by the PDPK1 gene.  It is implicated in the development and progression of melanomas.
The structure of PDPK1 can be divided into two domains; the kinase or catalytic domain and the PH domain. The PH domain functions mainly in the interaction of PDPK1 with phosphatidylinositol (3,4)-bisphosphate and phosphatidylinositol (3,4,5)-trisphosphate which is important in localization and activation of some of membrane associated PDPK1′s substrates including AKT.
The kinase domain has three ligand binding sites; the substrate binding site, the ATP binding site, and the docking site (also known as PIF pocket). Several PDPK1 substrates including S6K and Protein kinase C, require the binding at this docking site. Small molecule allosteric activators of PDPK1 were shown to selectively inhibit activation of substrates that require docking site interaction. These compounds do not bind to the active site and allow PDPK1 to activate other substrates that do not require docking site interaction. PDPK1 is constitutively active and at present, there are no known inhibitor proteins for PDPK1.
The activation of PDPK1′s main effector, AKT, is believed to require a proper orientation of the kinase and PH domains of PDPK1 and AKT at the membrane.
PDPK1 is a master kinase, which is crucial for the activation of AKT/PKB and many other AGC kinases including PKC, S6K, SGK. An important role for PDPK1 is in the signalling pathways activated by several growth factors and hormones including insulin signaling. 
Mice lacking PDPK1 die during early embryonic development, indicating that this enzyme is critical for transmitting the growth-promoting signals nescessary for normal mammalian development.
Mice that are deficient in PDPK1 have a ≈40% decrease in body mass, mild glucose intolerance, and are resistant to cancer brought about by hyperactivation of the PI3K pathway (PTEN+/-).
PDPK1 stands for 3-phosphoinositide-dependent protein kinase 1. PDPK1 functions downstream of PI3K through PDPK1′s interaction with membrane phospholipids including phosphatidylinositols, phosphatidylinositol (3,4)-bisphosphate and phosphatidylinositol (3,4,5)-trisphosphate. PI3K indirectly regulates PDPK1 by phosphorylating phosphatidylinositols which in turn generates phosphatidylinositol (3,4)-bisphosphate and phosphatidylinositol (3,4,5)-trisphosphate. However, PDPK1 is believed to be constitutively active and does not always require phosphatidylinositols for its activities.
Phosphatidylinositols are only required for the activation at the membrane of some substrates including AKT. PDPK1 however does not require membrane lipid binding for the efficient phosphorylation of most of its substrates in the cytosol (not at the cell membrane).
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Reference  Scortegagna M, Ruller C, Feng Y, Lazova R, Kluger H, Li JL et al. (2014). “Genetic inactivation or pharmacological inhibition of Pdk1 delays development and inhibits metastasis of Braf(V600E)::Pten(-/-) melanoma”. Oncogene 33 (34): 4330–9.  Mora A, Komander D, van Aalten DM, Alessi DR (April 2004). “PDK1, the master regulator of AGC kinase signal transduction”. Semin. Cell Dev. Biol. 15 (2): 161–70.  Frödin M, Antal TL, Dümmler BA, Jensen CJ, Deak M, Gammeltoft S et al. (October 2002). “A phosphoserine/threonine-binding pocket in AGC kinases and PDK1 mediates activation by hydrophobic motif phosphorylation”. EMBO J. 21 (20): 5396–407.