RESUMO
Signaling from JAK (Janus kinase) protein kinases to STAT (signal transducers and activators of transcription) transcription factors is key to many aspects of biology and medicine, yet the mechanism by which cytokine receptors initiate signaling is enigmatic. We present a complete mechanistic model for activation of receptor-bound JAK2, based on an archetypal cytokine receptor, the growth hormone receptor. For this, we used fluorescence resonance energy transfer to monitor positioning of the JAK2 binding motif in the receptor dimer, substitution of the receptor extracellular domains with Jun zippers to control the position of its transmembrane (TM) helices, atomistic modeling of TM helix movements, and docking of the crystal structures of the JAK2 kinase and its inhibitory pseudokinase domain with an opposing kinase-pseudokinase domain pair. Activation of the receptor dimer induced a separation of its JAK2 binding motifs, driven by a ligand-induced transition from a parallel TM helix pair to a left-handed crossover arrangement. This separation leads to removal of the pseudokinase domain from the kinase domain of the partner JAK2 and pairing of the two kinase domains, facilitating trans-activation. This model may well generalize to other class I cytokine receptors.
Assuntos
Janus Quinase 2/metabolismo , Receptores da Somatotropina/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Cisteína/química , Ativação Enzimática , Células HEK293 , Humanos , Janus Quinase 2/antagonistas & inibidores , Janus Quinase 2/química , Modelos Moleculares , Dados de Sequência Molecular , Mutação , Multimerização Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Receptores da Somatotropina/química , Receptores da Somatotropina/genéticaRESUMO
BACKGROUND: Deficiencies in daily ward rounds are increasingly identified. A ward safety checklist has recently been devised to improve the fast-paced surgical ward round. METHODS: Over 2 weeks the morning post-take surgical ward round was evaluated using the ward safety checklist. In order to avoid the Hawthorne effect, doctors involved were not aware their performance was being observed. RESULTS: One hundred patient encounters were evaluated. The three phases of the card safety checklist showed statistically significant improvement but for many components compliance was below 100%. CONCLUSION: Implementing this simple checklist has provided our unit with a starting point in how to overcome some of the deficiencies of the post-take surgical ward round.