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

Abstract Background: Mitogen-activated protein (MAP) kinases mediate the cellular response to stimuli such as pro-inflammatory cytokines and environmental stress. P38 γ is a new member of the MAP kinase family, and is expressed at its highest levels in skeletal muscle. P38 γ is 63% identical in sequence to P38 α . The structure of P38 α MAP kinase has been determined in the apo, 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 γ 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 γ 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 γ 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 γ exists as a monomer. Conclusions: Interactions mediated by phosphoryl-Thr183 induce structural changes that direct the domains and active-site residues of P38 γ 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.