Feline McDonough Sarcoma-like tyrosine kinase (Flt3) is a member of the class III tyrosine kinase receptor family. Ligand binding induces conformational changes in the Flt3 receptor, which facilitates its dimerization and autophosphorylation. Once fully active, Flt3 receptors can associate with growth factor receptor-bound protein 2 (Grb2), which then recruits Grb2-associated-binding protein 2 (Gab2). Consequently, Gab2 is phosphorylated and recruits tyrosine-protein phosphatase non-receptor type 11 (Ptpn11). The serine residue at position 623 in Gab2 is known to be involved in Ptpn11 binding (Zhang et al. 2000, Arnaud et al. 2004). The precise association mechanism of Gab2 and Ptpn11 is unclear. Interaction of Flt3 with Ptpn11 is known to trigger Stat5 activation in various pathological conditions.