Cytokine receptors play a pivotal role in many cellular processes. They initiate signalling cascades that regulate a vast range of vital physiological functions, including metabolism control, neural stem cell activation, inflammatory responses, bone development, as well as blood cell and immune cell development and growth. GHR is the member of the class I cytokine receptor family. This family does not possess an intrinsic kinase activity, however they bind JAK kinases via a conserved intracellular proline rich box1 motif, located a short distance from the cell membrane. A less conserved box2 sequence consisting of acidic and aromatic residues is located a short distance C-terminal of the box1. The box2 is also thought to play a role in interacting with JAKs and facilitating signal transduction from the receptor. The JAKs (âˆ½1150 amino acid) are multi-domain proteins possessing an N-terminal FERM (band 4.1, ezrin, radixin, moesin) domain followed by SH2, pseudokinase, and kinase domains. The FERM domain is required for receptor binding and the SH2 domain is also thought to be involved in receptor binding. Activation of the receptor results in JAK phosphorylation followed by further phosphorylation of multiple tyrosine residues on the intracellular domain of the receptor and subsequent phosphorylation of STATs. We sought to determine the structure of Box1-2 of GHR bound to FERM-SH2 domains of JAK2. We optimised a recombinant protein expression method resulting in high purity monodispersed solution with protein crystals identified from screening crystallisation conditions. Suitable crystals will be analysed to determine structural basis of JAK2 interaction with GHR.