PTPN11 and leukemia: The crystal structures include: (i) SHP2 in an autoinhibited, closed state (4dgp),38 (ii) the leukemia-associated SHP2E76K mutant in an active, open state (6crf),39 (iii) the PTPN11 tandem SH2 in complex with phosphopeptides (5df6, Eck96, 5x7b, 5x94),24,40,41 (iv) SHP1 (the closest homolog of SHP2) in an active, open state (3ps5).42 The crystal structures were determined under different experimental conditions and within different space groups, which resulted in different arrangements of the tandem SH2 (Fig. 5, Table 1).