Structure of the Pseudokinase VRK3 Reveals a Degraded Catalytic Site, a Highly Conserved Kinase Fold, and a Putative Regulatory Binding Site

123

Pseudokinases lack conserved motifs typically required for kinase activity. Nearly half of pseudokinases bind ATP, but only few retain phosphotransfer activity, leaving the functional role of nucleotide binding in most cases unknown. Janus kinases (JAKs) are nonreceptor tyrosine kinases with a tandem pseudokinase-kinase domain configuration, where the pseudokinase domain (JAK homology 2, JH2) has important regulatory functions and harbors mutations underlying hematological and immunological diseases. JH2 of JAK1, JAK2, and TYK2 all bind ATP, but the significance of this is unclear. We characterize the role of nucleotide binding in normal and pathogenic JAK signaling using comprehensive structure-based mutagenesis. Disruption of JH2 ATP binding in wildtype JAK2 has only minor effects, and in the presence of type I cytokine receptors, the mutations do not affect JAK2 activation. However, JH2 mutants devoid of ATP binding ameliorate the hyperactivation of JAK2 V617F. Disrupting ATP binding in JH2 also inhibits the hyperactivity of other pathogenic JAK2 mutants, as well as of JAK1 V658F, and prevents induction of erythrocytosis in a JAK2 V617F myeloproliferative neoplasm mouse model. Molecular dynamic simulations and thermal-shift analysis indicate that ATP binding stabilizes JH2, with a pronounced effect on the C helix region, which plays a critical role in pathogenic activation of JAK2. Taken together, our results suggest that ATP binding to JH2 serves a structural role in JAKs, which is required for aberrant activity of pathogenic JAK mutants. The inhibitory effect of abrogating JH2 ATP binding in pathogenic JAK mutants may warrant novel therapeutic approaches.T he Janus kinases (JAK1-3, TYK2) are a family of nonreceptor tyrosine kinases with essential functions in the regulation of hematopoiesis, the immune system, and cellular metabolism. JAKs interact specifically with various cytokine receptors and couple cytokine binding to cytoplasmic signaling cascades, including the signal transducers and activators of transcription (STAT) pathway. JAKs consist of an N-terminal FERM domain, an SH2-like (Src homology 2) domain, a pseudokinase domain (JAK homology 2, JH2), and the C-terminal tyrosine kinase domain (JH1). JH2 mediates critical regulatory functions in JAKs and primarily serves to inhibit basal JH1 activity. Experimental deletion of JH2 increases JH1 activity in full-length JAK in the absence of stimulation (1-3), and in recombinant systems addition of JH2 suppresses JH1 activity (4-6). JH2 is, however, also required for ligand-induced activation of full-length JAKs in cell (1-3, 6, 7). The regulatory functions of JH2 are corroborated by the multitude of human disease mutations identified in the domain. The most common JAK2 mutation, V617F, leads to cytokine-independent signaling through the exclusively JAK2-dependent homotypic receptors for erythropoietin (EPO), granulocyte colony stimulating factor (G-CSF), and thrombopoietin (8). The V617F mutation is found in ∼95% of patients with polycythemia vera (PV) (9...

Section: Discussionmentioning

confidence: 99%

ATP binding to the pseudokinase domain of JAK2 is critical for pathogenic activation

Hammarén

Ungureanu

Grisouard

et al. 2015

123

“…Vector-transformed Escherichia coli (BL21 Rosetta) was grown and purified as described in ref. 31, but with the addition of 750 mM NaCl before concentration of haspin by ultrafiltration. For selenomethionine labeling, the cells were grown in MD medium with 40 mg/L of selenomethionine for 12 h at 18°C, and the protein was purified as the native protein.…”

Section: Methodsmentioning

confidence: 99%

“…A thermal stability assay using differential scanning fluorimetry for nucleotide and cation binding also was performed, as described in ref. 31.…”

Section: Methodsmentioning

confidence: 99%

Structure and functional characterization of the atypical human kinase haspin

Eswaran

Patnaik

Filippakopoulos

et al. 2009

Self Cite

152

159

The protein kinase haspin/Gsg2 plays an important role in mitosis, where it specifically phosphorylates Thr-3 in histone H3 (H3T3). Its protein sequence is only weakly homologous to other protein kinases and lacks the highly conserved motifs normally required for kinase activity. Here we report structures of human haspin in complex with ATP and the inhibitor iodotubercidin. These structures reveal a constitutively active kinase conformation, stabilized by haspin-specific inserts. Haspin also has a highly atypical activation segment well adapted for specific recognition of the basic histone tail. Despite the lack of a DFG motif, ATP binding to haspin is similar to that in classical kinases; however, the ATP ␥-phosphate forms hydrogen bonds with the conserved catalytic loop residues Asp-649 and His-651, and a His651Ala haspin mutant is inactive, suggesting a direct role for the catalytic loop in ATP recognition. Enzyme kinetic data show that haspin phosphorylates substrate peptides through a rapid equilibrium random mechanism. A detailed analysis of histone modifications in the neighborhood of H3T3 reveals that increasing methylation at Lys-4 (H3K4) strongly decreases substrate recognition, suggesting a key role of H3K4 methylation in the regulation of haspin activity.ATP binding ͉ histone modification ͉ phosphorylation mechanism ͉ germ cell-specific gene 2 (Gsg2) ͉ mitosis E ukaryotic protein kinases (ePKs) constitute a large group of enzymes that regulate a vast diversity of cellular processes. Kinase activity depends on a number of highly conserved sequence motifs required for ATP/Mg 2ϩ binding and catalysis. About 10% of human ePKs lack one or more essential catalytic motifs and have been initially classified as inactive pseudokinases (1). However, a number of such proteins are active kinases, including haspin [haploid germ cell-specific nuclear protein kinase, encoded by Germ cell-specific gene 2 (Gsg2)]. Haspin lacks both the conserved ATP/Mg 2ϩ binding motif Asp-Phe-Gly (DFG), which is replaced by Asp-Tyr-Thr (DYT), and the Ala-Pro-Glu (APE) motif usually found at the C terminus of the activation segment (2). In addition, haspin shares only weak sequence homology with ePKs and contains a highly divergent kinase domain with several unique inserts (2, 3). Haspin mRNA is abundant in testis and also present in somatic cells (4, 5), and orthologues are found throughout eukaryotic phyla (2). Ectopically expressed haspin localizes to the nucleus in interphase and to the chromosomes in mitosis (4, 6), while depletion of haspin leads to premature chromatid separation, failure of chromosome alignment, and a block in mitosis in a prometaphase-like state (6, 7).Haspin autophosphorylates in vitro (4, 6, 8) and phosphorylates its only currently known substrate, histone H3, at threonine-3 (H3T3ph) both in vitro and in cells (6). H3T3 phosphorylation occurs specifically during mitosis and is particularly prominent at inner centromere regions (6, 7, 9). Recently, H3T3ph has been suggested to relieve an inhibitory effect of ...

“…Pseudokinases, which represent Ϸ10% of all human kinases, are assumed to act as scaffolds or allosteric regulators rather than enzymes and are still relatively poorly characterized as a group. The structures of two pseudokinase domains have been reported so far, those of Ca 2ϩ /calmodulin-activated Ser-Thr kinase (CASK) (13) and vaccinia-related kinase 3 (VRK3) (14).…”

mentioning

confidence: 99%

Structural analysis of the catalytically inactive kinase domain of the human EGF receptor 3

Jura¹,

Shan

Cao³

et al. 2009

279

310

The kinase domain of human epidermal growth factor receptor (HER) 3/ErbB3, a member of the EGF receptor (EGFR) family, lacks several residues that are critical for catalysis. Because catalytic activity in EGFR family members is switched on by an allosteric interaction between kinase domains in an asymmetric kinase domain dimer, HER3 might be specialized to serve as an activator of other EGFR family members. We have determined the crystal structure of the HER3 kinase domain and show that it appears to be locked into an inactive conformation that resembles that of EGFR and HER4. Although the crystal structure shows that the HER3 kinase domain binds ATP, we confirm that it is catalytically inactive but can serve as an activator of the EGFR kinase domain. The HER3 kinase domain forms a dimer in the crystal, mediated by hydrophobic contacts between the N-terminal lobes of the kinase domains. This N-lobe dimer closely resembles a dimer formed by inactive HER4 kinase domains in crystal structures determined previously, and molecular dynamics simulations suggest that the HER3 and HER4 N-lobe dimers are stable. The kinase domains of HER3 and HER4 form similar chains in their respective crystal lattices, in which N-lobe dimers are linked together by reciprocal exchange of C-terminal tails. The conservation of this tiling pattern in HER3 and HER4, which is the closest evolutionary homolog of HER3, might represent a general mechanism by which this branch of the HER receptors restricts ligand-independent formation of active heterodimers with other members of the EGFR family.EGFR ͉ human epidermal growth factor receptor 3 ͉ human epidermal growth factor receptor4 ͉ receptor oligomerization