ONE KINASE, MULTIPLE CONFORMATIONS: PROBING THE CONFORMATIONAL LANDSCAPE OF PDK1 WITH SMALL MOLECULES

SACERDOTI, M; GROSS, LZF; FROESE, KARIN; SUESS, E; GHODE, A; RILEY, A; CAPELLARI, V; KLINKE, S; ANAND, GS; POTTER, B; ARAMENDIA, P; LEROUX, AE; BIONDI, RM

Mendoza

Congreso; LVI Reunión Científica anual SAIB y XV de SAMIGE; 2020

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Phosphoinositide-dependentprotein kinase 1 (PDK1) is a master kinase of the PI3-kinase signalling pathwaythat phosphorylates at least 23 other evolutionary related AGC kinases. It hasan N-terminal kinase domain, a linker region and a C-terminal PH domain. Overthe years, our laboratory has used a chemical and structural biology approachto study and characterize the bidirectional allosteric regulation between the PIF-pocket, a regulatory site located onthe small lobe of the kinase domain, and the ATP-Binding site of PDK1. Themechanism of activation of PDK1, mediated by the PIF-pocket regulatory site, is conserved within the large group ofAGC kinases, including the isoforms of PKC, Akt, SGK, S6K, RSK, MSK, etc.Phosphorylation by PDK1 is required for the activity of all substrates: theyare phosphorylated either constitutively or with different timing uponPI3-kinase activation. Most substrates, like S6K, SGK, PKC, PRK/PKN, rely on a dockinginteraction where a C-terminal hydrophobic motif (HM) interacts with the PIF-pocket of PDK1. Interestingly, the interaction with the PIF-pocket of PDK1 is not a requirement for the phosphorylation ofPKB/Akt after PI3-kinase activation, but both proteins have a PH domain thatcan bind PIP3 at the cell membrane and colocalize. However, webelieve that other mechanisms must regulate that interaction since there arereports of PKB/Akt activation by PDK1 in the absence of PIP3. PDK1has recently been described to dimerize. We describe the effect of different inositol poliphosphorylatedmolecules and present results of a screening performed in order to find smallcompounds to regulate dimer formation. We conclude that PDK1 could exist in asan equilibrium of dynamic conformations that impact on the selectiveinteractions with substrates. We suggest dimerization couldalso be part of the mechanism by which PDK1 phosphorylates some substrates likePKB/Akt. The regulation of dimerization is not linked to the bidirectionalallosteric communication between the PIF-pocketand the ATP-Binding site. This potential new regulatory mechanism could be newapproach to develop innovative drugs to target PDK1 and achieve, for example,PKB/Akt selective inhibition.