A new regulatory switch in a JAK protein kinase.

Members of the JAK family of protein kinases mediate signal transduction from cytokine receptors to transcription factor activation. Over-stimulation of these pathways is causative in immune disorders like rheumatoid arthritis, psoriasis, lupus, and Crohn's disease. A search for selective inhibitors of a JAK kinase has led to our characterization of a previously unknown kinase conformation arising from presentation of Tyr962 of TYK2 to an inhibitory small molecule via an H-bonding interaction.