CRYSTAL-STRUCTURE OF JNK3 - A KINASE IMPLICATED IN NEURONAL APOPTOSIS

Background: The c-Jun N-terminal kinases (JNKs) are members of the mit ogen-activated protein (MAP) kinase family, and regulate signal transd uction in response to environmental stress. Activation and nuclear loc alization of JNK3, a neuronal-specific isoform of JNK, has been associ ated with hypoxic and ischemic damage of CA1 neurons in the hippocampu s. Knockout mice lacking JNK3 showed reduced apoptosis of hippocampal neurons and reduced seizure induced by kainic acid, a glutamate-recept or agonist. Thus, JNK3 may be important in the pathology of neurologic al disorders and is of significant medical interest. Results: We repor t here the structure of unphosphorylated JNK3 in complex with adenylyl imidodiphosphate, an ATP analog. JNK3 has a typical kinase fold, with the ATP-binding site situated within a cleft between the N- and C-ter minal domains. In contrast to other known MAP kinase structures, the A TP-binding site of JNK3 is well ordered; the glycine-rich nucleotide-b inding sequence forms a beta-strand-turn-beta-strand structure over th e nucleotide. Unphosphorylated JNK3 assumes an open conformation, in w hich the N- and C-terminal domains are twisted apart relative to their positions in cAMP-dependent protein kinase. The rotation leads to the misalignment of some of the catalytic residues. The phosphorylation l ip of JNK3 partially blocks the substrate-binding site. Conclusions: T his is the first JNK structure to be determined, providing a unique op portunity to compare structures from the three MAP kinase subfamilies. The structure reveals atomic-level details of the shape of JNK3 and t he interactions between the kinase and the nucleotide. The misalignmen t of catalytic residues and occlusion of the active site by the phosph orylation lip may account for the low activity of unphosphorylated JNK 3. The structure provides a framework for understanding the substrate specificity of different JNK isoforms, and should aid the design of se lective JNK3 inhibitors.