Crystal structure of the kinase and JM domain of human Flt3. (A) The section highlighted in red shows Tyr842 pointing into the active site of the activation loop, thereby stabilizing the inhibited conformation of Flt3 by forming a hydrogen bond with Asp811, which in turn is linked to Arg834 through an ion pair. (B) Relative conformation of Tyr842 (Y842), Asp811 (D811), Arg834 (R834), and Asp835 (D835) in autoinhibited Flt3.