The structure of phosphorylated P38γ is monomeric and reveals a conserved activation-loop conformation

Background: Mitogen-activated protein (MAP) kinases mediate the cellular response to stimuli such as pro-inflammatory cytokines and environmental stress. P38 gamma is a new member of the MAP kinase family, and is expressed at its highest levels in skeletal muscle. P38 gamma is 63% identical in sequence to P38 alpha. The structure of P38 alpha MAP kinase has been determined in the ape, unphosphorylated, inactive form. The structures of apo unphosphorylated ERK2, a related MAP kinase, and apo phosphorylated ERK2 have also been determined. Results: We have determined the structure of doubly phosphorylated P38 gamma in complex with an ATP analog by X-ray crystallography. This is the first report of a structure of an activated kinase in the P38 subfamily, and the first bound to a nucleotide. P38 gamma residue phosphoryl-Thr183 forms hydrogen bonds with five basic amino acids, and these interactions induce an interdomain rotation. The conformation of the activation loop of P38 gamma is almost identical to that observed in the structure of activated ERK2. However, unlike ERK2, the crystal structure and solution studies indicate that activated P38 gamma exists as a monomer. Conclusions: Interactions mediated by phosphoryl-Thr183 induce structural changes that direct the domains and active-site residues of P38 gamma into a conformation consistent with catalytic activity. The conformation of the phosphorylation loop is likely to be similar in all activated MAP kinases, but not all activated MAP kinases form dimers.