TAB1-Induced Autoactivation of p38α Mitogen-Activated Protein Kinase Is Crucially Dependent on Threonine 185

p38 alpha mitogen-activated protein kinase is essential to cellular homeostasis. Two principal mechanisms to activate p38 alpha exist. The first relies on dedicated dual-specificity kinases such as mitogen-activated protein kinase kinase (MAP2K) 3 (MKK3) or 6 (MKK6), which activate p38 alpha by phosphorylating Thr180 and Tyr182 within the activation segment. The second is by autophosphorylation of Thr180 and Tyr182 in cis, mediated by p38 alpha binding the scaffold protein TAB1. The second mechanism occurs during myocardial ischemia, where it aggravates myocardial infarction. Based on the crystal structure of the p38 alpha -TAB1 complex we replaced threonine 185 of p38 alpha with glycine (T185G) to prevent an intramolecular hydrogen bond with Asp150 from being formed. This mutation did not interfere with TAB1 binding to p38 alpha. However, it disrupted the consequent long-range effect of this binding event on the distal activation segment, releasing the constraint on Thr180 that oriented its hydroxyl for phosphotransfer. Based on assays performed in vitro and in vivo, the autoactivation of p38 alpha (T185G) was disabled, while its ability to be activated by upstream MAP2Ks and to phosphorylate downstream substrates remained intact. Furthermore, myocardial cells expressing p38 alpha (T185G) were resistant to injury. These findings reveal a mechanism to selectively disable p38 alpha autoactivation and its consequences, which may ultimately circumvent the toxicity associated with strategies that inhibit p38 alpha kinase activity under all circumstances, such as with ATP-competitive inhibitors.