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JAK2 activation by growth hormone and other cytokines.

Waters MJ, Brooks AJ - Biochem. J. (2015)

Bottom Line: Binding of the bivalent ligand reorientates and rotates the receptor subunits, resulting in a transition from a form with parallel TMDs to one where the TMDs separate at the point of entry into the cytoplasm.This results in phosphorylation and activation of STATs and other signalling pathways linked to this receptor which then regulate postnatal growth, metabolism and stem cell activation.We believe that this model will apply to most if not all members of the class I cytokine receptor family, and will be useful in the design of small antagonists and agonists of therapeutic value.

View Article: PubMed Central - PubMed

Affiliation: *Institute for Molecular Bioscience, The University of Queensland Institute, QLD 4072, Australia.

ABSTRACT
Growth hormone (GH) and structurally related cytokines regulate a great number of physiological and pathological processes. They do this by coupling their single transmembrane domain (TMD) receptors to cytoplasmic tyrosine kinases, either as homodimers or heterodimers. Recent studies have revealed that many of these receptors exist as constitutive dimers rather than being dimerized as a consequence of ligand binding, which has necessitated a new paradigm for describing their activation process. In the present study, we describe a model for activation of the tyrosine kinase Janus kinase 2 (JAK2) by the GH receptor homodimer based on biochemical data and molecular dynamics simulations. Binding of the bivalent ligand reorientates and rotates the receptor subunits, resulting in a transition from a form with parallel TMDs to one where the TMDs separate at the point of entry into the cytoplasm. This movement slides the pseudokinase inhibitory domain of one JAK kinase away from the kinase domain of the other JAK within the receptor dimer-JAK complex, allowing the two kinase domains to interact and trans-activate. This results in phosphorylation and activation of STATs and other signalling pathways linked to this receptor which then regulate postnatal growth, metabolism and stem cell activation. We believe that this model will apply to most if not all members of the class I cytokine receptor family, and will be useful in the design of small antagonists and agonists of therapeutic value.

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Related in: MedlinePlus

Transition of the GH receptor TMDsThe interaction of the GH receptor TMDs in the inactive parallel State 1 and active crossover State 2 are shown.
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Figure 3: Transition of the GH receptor TMDsThe interaction of the GH receptor TMDs in the inactive parallel State 1 and active crossover State 2 are shown.

Mentions: Our group sought to understand these findings through molecular dynamics modelling, first in vacuo, then in DPPC membrane bilayers [44]. Using coarse grain models to model the approach of two GH receptor TMD helices in DPPC, it was observed that the helices first converge at their C-termini when their centres of mass are approximately 20 Å apart. The main reason for this is repulsive interactions at the N-termini. As the helices approach more closely, aromatic Phe-276 and Phe-283 interact, and together with Thr–Thr hydrogen bonding, this stabilizes a parallel form with a helix interaction face evident in the cysteine crosslink pattern. Further approach, as would be induced by ligand binding, resulted in a rotation of helices and separation of their C-termini, so that the two glycines of the conserved GxxG motif packed together. This meant the phenylalanines were rotated out of contact, resulting in a left-handed crossover dimer with lowest PMF (potential of mean force) (Figure 3). The PMF of the parallel form (State 1) is close to that of the crossover form (State 2) so that the transition between the two forms would be relatively facile. Importantly, the predicted free energy of binding for the two helices (approximately 10 kcal/mol) indicated little monomer will be present. The latter prediction was borne out by homo-FRET efficiency measurements at the cell surface using confocal microscopy which showed that little monomer was detectible at moderate expression levels. It was gratifying that it was possible to recapitulate State 2 in silico by introducing disulfide bonds at Glu-260 and Ile-270 in the JM and upper TMD helix locations because this mutant had substantial constitutive activity experimentally [44].


JAK2 activation by growth hormone and other cytokines.

Waters MJ, Brooks AJ - Biochem. J. (2015)

Transition of the GH receptor TMDsThe interaction of the GH receptor TMDs in the inactive parallel State 1 and active crossover State 2 are shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4325515&req=5

Figure 3: Transition of the GH receptor TMDsThe interaction of the GH receptor TMDs in the inactive parallel State 1 and active crossover State 2 are shown.
Mentions: Our group sought to understand these findings through molecular dynamics modelling, first in vacuo, then in DPPC membrane bilayers [44]. Using coarse grain models to model the approach of two GH receptor TMD helices in DPPC, it was observed that the helices first converge at their C-termini when their centres of mass are approximately 20 Å apart. The main reason for this is repulsive interactions at the N-termini. As the helices approach more closely, aromatic Phe-276 and Phe-283 interact, and together with Thr–Thr hydrogen bonding, this stabilizes a parallel form with a helix interaction face evident in the cysteine crosslink pattern. Further approach, as would be induced by ligand binding, resulted in a rotation of helices and separation of their C-termini, so that the two glycines of the conserved GxxG motif packed together. This meant the phenylalanines were rotated out of contact, resulting in a left-handed crossover dimer with lowest PMF (potential of mean force) (Figure 3). The PMF of the parallel form (State 1) is close to that of the crossover form (State 2) so that the transition between the two forms would be relatively facile. Importantly, the predicted free energy of binding for the two helices (approximately 10 kcal/mol) indicated little monomer will be present. The latter prediction was borne out by homo-FRET efficiency measurements at the cell surface using confocal microscopy which showed that little monomer was detectible at moderate expression levels. It was gratifying that it was possible to recapitulate State 2 in silico by introducing disulfide bonds at Glu-260 and Ile-270 in the JM and upper TMD helix locations because this mutant had substantial constitutive activity experimentally [44].

Bottom Line: Binding of the bivalent ligand reorientates and rotates the receptor subunits, resulting in a transition from a form with parallel TMDs to one where the TMDs separate at the point of entry into the cytoplasm.This results in phosphorylation and activation of STATs and other signalling pathways linked to this receptor which then regulate postnatal growth, metabolism and stem cell activation.We believe that this model will apply to most if not all members of the class I cytokine receptor family, and will be useful in the design of small antagonists and agonists of therapeutic value.

View Article: PubMed Central - PubMed

Affiliation: *Institute for Molecular Bioscience, The University of Queensland Institute, QLD 4072, Australia.

ABSTRACT
Growth hormone (GH) and structurally related cytokines regulate a great number of physiological and pathological processes. They do this by coupling their single transmembrane domain (TMD) receptors to cytoplasmic tyrosine kinases, either as homodimers or heterodimers. Recent studies have revealed that many of these receptors exist as constitutive dimers rather than being dimerized as a consequence of ligand binding, which has necessitated a new paradigm for describing their activation process. In the present study, we describe a model for activation of the tyrosine kinase Janus kinase 2 (JAK2) by the GH receptor homodimer based on biochemical data and molecular dynamics simulations. Binding of the bivalent ligand reorientates and rotates the receptor subunits, resulting in a transition from a form with parallel TMDs to one where the TMDs separate at the point of entry into the cytoplasm. This movement slides the pseudokinase inhibitory domain of one JAK kinase away from the kinase domain of the other JAK within the receptor dimer-JAK complex, allowing the two kinase domains to interact and trans-activate. This results in phosphorylation and activation of STATs and other signalling pathways linked to this receptor which then regulate postnatal growth, metabolism and stem cell activation. We believe that this model will apply to most if not all members of the class I cytokine receptor family, and will be useful in the design of small antagonists and agonists of therapeutic value.

Show MeSH
Related in: MedlinePlus