Poster Presentation The 43rd Lorne Conference on Protein Structure and Function 2018

Structural studies of full length JAK1 (#185)

Nicholas PD Liau , Nadia J Kershaw , Artem Laktyushin , Jeff J Babon , Nicos A Nicola

The Janus Kinases (JAKs) are tyrosine kinases which are constitutively attached to the intracellular domain of a cytokine receptor. Upon cytokine stimulation, they phosphorylate downstream substrates, including the Signal Transducer and Activator of Transcription (STAT) transcription factors. Phosphorylated STATs enter the nucleus and upregulate particular gene sets, driving a biological response.

Mutations to the JAKs causing overactive signalling have been associated with a group of diseases known as the myeloproliferative neoplasms, as well as some cancers. To ensure JAK signalling is only active when required, the JAKs are switched off under resting conditions, and only become activated in response to cytokine signalling (except for some constitutively active JAK disease-causing mutants).

The JAKs have four domains. The kinase domain phosphorylates substrates, however, the other three domains are also involved in the regulation of the activity of the kinase domain. No high-resolution structure of all four domains of JAK together has been reported, so the mechanism by which these domains regulate kinase activity is largely unexplained. A high-resolution structure including all JAK domains may help to explain how its kinase activity is regulated.

We have developed a method to recombinantly express and purify large amounts of full length JAK1 for structural studies, along with two of its physiological binding partners. We have undertaken studies on this protein using X-ray crystallography, SAXS and Cryo-EM with a view to solving a high-resolution structure of full length JAK1. To date, we have only obtained low resolution information about full length JAK1, which suggests that a significant amount of inter-domain flexibility exists within the protein.