A Complex Interplay of Anionic Phospholipid Binding Regulates 3-Phosphoinositide-Dependent-Kinase-1 Homodimer Activation

3-Phosphoinositide-dependent-Kinase-1 is a master regulator whereby its PI3-kinase-dependent dysregulation in human pathologies is well documented. Understanding the direct role for PtdIns(3,4,5)P3 and other anionic phospholipids in the regulation of PDK1 conformational dynamics and its downstream activation remains incomplete. Using advanced quantitative-time-resolved imaging, FCS and molecular modelling, we show an interplay of antagonistic binding effects of PtdIns(3,4,5)P3 and other anionic phospholipids, regulating activated PDK1 homodimers. We demonstrate that phosphatidylserine maintains PDK1 in an inactive conformation. The dysregulation of the PI3K pathway affects the spatio-temporal and conformational dynamics of PDK1 and the activation of its downstream substrates. We establish an anionic-phospholipid-dependent model for PDK1 regulation, depicting the conformational dynamics of multiple homodimer states. The dysregulation of the PI3K pathway perturbs equilibrium between the PDK1 homodimer conformations. Our findings indicate that the alteration of specific basic residues of PDK1-PH domain leads to its constitutive activation, a potential significance in different types of carcinomas.