Crystal structures of the JAK2 pseudokinase domain and the pathogenic mutant V617F

Abstract

Human JAK2 tyrosine kinase mediates signaling through numerous cytokine receptors. The JAK2 JH2 pseudokinase domain negatively regulates the activity of the JH1 kinase domain. The structures of wild-type JH2 and of the dominant V617F mutant provide a solid foundation for discerning the mechanism of action of the JH2 domain in normal JAK signaling and in dysregulated signaling that causes disease. The protein tyrosine kinase JAK2 mediates signaling through numerous cytokine receptors. JAK2 possesses a pseudokinase domain (JH2) and a tyrosine kinase domain (JH1). Through unknown mechanisms, JH2 regulates the catalytic activity of JH1, and hyperactivating mutations in the JH2 region of human JAK2 cause myeloproliferative neoplasms (MPNs). We showed previously that JAK2 JH2 is, in fact, catalytically active. Here we present crystal structures of human JAK2 JH2, including both wild type and the most prevalent MPN mutant, V617F. The structures reveal that JH2 adopts the fold of a prototypical protein kinase but binds Mg-ATP noncanonically. The structural and biochemical data indicate that the V617F mutation rigidifies α-helix C in the N lobe of JH2, facilitating trans-phosphorylation of JH1. The crystal structures of JH2 afford new opportunities for the design of novel JAK2 therapeutics targeting MPNs.