Mapping of a region within the N terminus of Jak1 involved in cytokine receptor interaction

Janus kinase 1 (Jak1) is a cytoplasmic tyrosine kinase that noncovalently a ssociates with a variety of cytokine receptors. Here we show that the in vi tro translated N-terminal domains of Jak1 are sufficient for binding to a b iotinylated peptide comprising the membrane-proximal 73 amino acids of gp13 0, the signal-transducing receptor chain of interleukin-6-type cytokines. B y the fold recognition approach amino acid residues 36-112 of Jah1 were pre dicted to adopt a beta -grasp fold, and a structural model was built using ubiquitin as a template. Substitution of Tyr(107) to alanine, a residue con served Among Jaks and involved in hydrophobic core interactions of the prop osed beta -grasp domain, abrogated binding of full-length Jak1 to gp130 in COS-7 transfectants. By further mutagenesis we identified the loop 4 region of the Jak1 beta -grasp domain as essential for gp130 association and gp13 0-mediated signal transduction. In Jak1-deficient U4C cells reconstituted w ith the loop 4 Jak1 mutants L80A/Y81A and Delta (Tyr(81)-Ser(84)), the inte rferon-gamma, interferon-a, and interleukin-6 responses were similarly impa ired. Thus, loop 4 of the beta -grasp domain plays a role in the associatio n of Jak1 with both class I and II cytokine receptors. Taken together the s tructural model and the mutagenesis data provide further insight into the i nteraction of Janus kinases with cytokine receptors.