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

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

Mendoza

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

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Phosphoinositide-dependent protein kinase 1 (PDK1) is a master kinase of the PI3-kinase signalling pathway that phosphorylates at least 23 other evolutionary related AGC kinases. It has an N-terminal kinase domain, a linker region and a C-terminal PH domain. Over the years, our laboratory has used a chemical and structural biology approach to study and characterize the bidirectional allosteric regulation between the PIF-pocket, a regulatory site located on the small lobe of the kinase domain, and the ATP-Binding site of PDK1. The mechanism of activation of PDK1, mediated by the PIF-pocket regulatory site, is conserved within the large group of AGC kinases, including the isoforms of PKC, Akt, SGK, S6K, RSK, MSK, etc. Phosphorylation by PDK1 is required for the activity of all substrates: they are phosphorylated either constitutively or with different timing upon PI3-kinase activation. Most substrates, like S6K, SGK, PKC, PRK/PKN, rely on a docking interaction 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 of PKB/Akt after PI3-kinase activation, but both proteins have a PH domain that can bind PIP3 at the cell membrane and colocalize. However, we believe that other mechanisms must regulate that interaction since there are reports of PKB/Akt activation by PDK1 in the absence of PIP3. PDK1 has recently been described to dimerize. We describe the effect of different inositol poliphosphorylated molecules and present results of a screening performed in order to find small compounds to regulate dimer formation. We conclude that PDK1 could exist in as an equilibrium of dynamic conformations that impact on the selective interactions with substrates. We suggest dimerization could also be part of the mechanism by which PDK1 phosphorylates some substrates like PKB/Akt. The regulation of dimerization is not linked to the bidirectional allosteric communication between the PIF-pocket and the ATP-Binding site. This potential new regulatory mechanism could be new approach to develop innovative drugs to target PDK1 and achieve, for example, PKB/Akt selective inhibition.