p38α mitogen-activated protein kinase (MAPK) is generally activated by dual phosphorylation but has also been shown to exhibit alternative activation modes. One of these modes included a direct interaction with phosphatidylinositol ether lipid analogues (PIA) inducing p38α autoactivation and apoptosis. Perifosine, an Akt inhibitor in phase II clinical trials, also showed p38α activation properties similarly to those of PIAs. The crystal structures of p38α in complex with PIA23, PIA24 and perifosine provide insights into this unique activation mode. The activating molecules bind a unique hydrophobic binding site in the kinase C′-lobe formed in part by the MAPK insert region. In addition, there are conformational changes in the short αEF/αF loop region that acts as an activation switch, inducing autophosphorylation. Structural and biochemical characterization of the αEF/αF loop identified Trp197 as a key residue in the lipid binding and in p38α catalytic activity. The lipid binding site also accommodates hydrophobic inhibitor molecules and, thus, can serve as a novel p38α-target for specific activation or inhibition, with novel therapeutic implications.
Bibliographical noteFunding Information:
The research was supported by the US–Israel Binational Science Foundation 2007154 awarded to O.L., P.A.D. and by the Israel Science Foundation Research Center of Excellence 180/09 awarded to OL. We would like to thank Dr. Mario Lebendiker from the Protein Purification Unit for his continuous helpful advice and assistance and Dr. Deborah E. Shalev for insightful discussions—both form the Wolfson Centre for Applied Structural Biology. We would like to thank Michal Meas for her assistance in the ITC analysis. We also thank the staff of ESRF, Grenoble, France, for their outstanding help by maintaining and upgrading the facility.
- MAP kinase
- alternative activation modes
- protein structure