The p38β Mitogen-activated Protein Kinase Possesses an Intrinsic Autophosphorylation Activity, Generated by a Short Region Composed of the α-G Helix and MAPK Insert

Background: Kinases, involved in all processes of life, are enzymes capable of self-activation. MAP kinases, a kinase subfamily, do not self-activate. Results: We found that p38 is a unique MAP kinase that can self-activate. Significance: Through this we disclosed the element responsible for self-activation. Conclusion: Minor differences between kinases impose dramatic differences on their self-activation property.Protein kinases are regulated by a large number of mechanisms that vary from one kinase to another. However, a fundamental activation mechanism shared by all protein kinases is phosphorylation of a conserved activation loop threonine residue. This is achieved in many cases via autophosphorylation. The mechanism and structural basis for autophosphorylation are not clear and are in fact enigmatic because this phosphorylation occurs when the kinase is in its inactive conformation. Unlike most protein kinases, MAP kinases are not commonly activated by autophosphorylation but rather by MEK-dependent phosphorylation. Here we show that p38, a p38 isoform that is almost identical to p38, is exceptional and spontaneously autoactivates by autophosphorylation. We identified a 13-residue-long region composed of part of the G-helix and the MAPK insert that triggers the intrinsic autophosphorylation activity of p38. When inserted into p38, this fragment renders it spontaneously active in vitro and in mammalian cells. We further found that an interaction between the N terminus and a particular region of the C-terminal extension suppresses the intrinsic autophosphorylation of p38 in mammalian cells. Thus, this study identified the structural motif responsible for the unique autophosphorylation capability of p38 and the motif inhibiting this activity in living cells. It shows that the MAPK insert and C-terminal extension, structural motifs that are unique to MAPKs, play a critical role in controlling autophosphorylation.