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[[Image:MyJak2.jpg|thumb|250px|left|Not, "just another kinase". Picture from Protein Data Bank.]]

Janus Kinase 2 is a non-receptor janus kinase, a protein which is part of the tyrosine kinases. These group of kinases are the primary intracellular mediators of cytokine signaling and are involved in the control of cellular growth. As a non-receptor kinase, Jak 2 has a cytoplasmic enzyme which catalyzes the transfer of a phosphate group through phosphorylation to the tyrosine residue in the protein.  Such an enzyme plays a crucial role in regulating various cellular functions by switching on or off additional enzymes within the cell. <ref> Hanks, SK., Quinn, AM., Hunter, T. (1988). The protein kinase family: conserved features and deduced phylogeny of the catalytic domains. Science 241 (4861): 42–52. doi:10.1126/science.3291115. PMID 3291115. </ref> Such phosphorylation is a reversible process, and used in many different pathways as a method to control cellular activity. However kinases like Jak2, have enzymes which add phosphate groups to hydroxyl side chains as can be seen in the diagram. <ref> Hudel, H. [Internet]. Irvine [CA]. Center for Biomembrane Systems at UC Irvine; c2013. [Updated 2013 Jan 3; cited 2013 March 23]. Available from: http://bass.bio.uci.edu </ref> [[Image:Phosphorylation.png]]

<Structure load='2b7a' size='350' frame='true' align='right' caption='3-D Structure of Jak2 as created in Protein Data Bank' scene='Insert optional scene name here' />

[[Image:Jak2structure.png|thumb|300px|left|Ribbon representation of Jak2 structure as determined by Dr. Isabelle S. Lucet et al]]

The structure of Jak 2 can be broken down into seven separate components, as seen in the pictured diagram to the left. The top, gray, portion of the protein was found to be the N-terminal lobe (residues 840-931). This loop is comprised of a 5-stranded anti-parallel beta-sheet (Beta1 - 5) and one alpha-helix (alpha C). The large dark green portion seen on the bottom is the COOH-terminal lobe. This carboxylic acid lobe is comprised of 8 alpha-helices (alpha D-alpha K), and 3 3/10 helices (3/10B, 3/10C, 3/10D), and 3 pairs of anti-parallel Beta-strands (Beta7-8, 6-9, and 10-11). The orange portion in the middle-right of the protein is the glycine loop which makes contacts with the activation loop and catalytic loop. This glycine loop, while small, is of great importance, as it is known to be essential in substrate and nucleotide binding. In yellow, to the top-left, there is a hinge region present which aids in molecule interactions. The blue section in the low middle is the catalytic loop, the red loop to the right is the activation loop and finally the dark blue section towards the bottom-right is the JAK2 lip which contains one 3/10C helix and one alpha-helix connected by a short linker. <ref> ) Lucet, I., Fantino, E., & Styles, M. (2005). The structural basis of janus kinase 2 inhibition by a potent and specific pan-janus kinase inhibitor. Blood, 107, 176-183. doi: 10.1182/blood-2005-06-2413 http://bloodjournal.hematologylibrary.org/content/107/1/176.full.pdf </ref>