Single Ion Pair Is Essential for Stabilizing SHP2's Open Conformation

Src-homology-2-domain-containing PTP-2 (SHP2) is a widely expressed signaling enzyme whose misregulation is associated with multiple human pathologies. SHP2's enzymatic activity is controlled by a conformational equilibrium between its autoinhibited ("closed") state and its activated ("open") state. Although SHP2's closed state has been extensively characterized, the putative structure of its open form has only been revealed in the context of a highly activated mutant (E76K), and no systematic studies of the biochemical determinants of SHP2's open-state stabilization have been reported. To identify amino-acid interactions that are critical for stabilizing SHP2's active state, we carried out a mutagenic study of residues that lie at potentially important interdomain interfaces of the open conformation. The open/closed equilibria of the mutants were evaluated, and we identified several interactions that contribute to the stabilization of SHP2's open state. In particular, our findings establish that an ion pair between glutamate 249 on SHP2's PTP domain and arginine 111 on an interdomain loop is the key determinant of SHP2's open-state stabilization. Mutations that disrupt the R111/E249 ion pair substantially shift SHP2's open/closed equilibrium to the closed state, even compared to wild-type SHP2's basal-state equilibrium, which strongly favors the closed state. To the best of our knowledge, the ion-pair variants uncovered in this study are the first known SHP2 mutants in which autoinhibition is augmented with respect to the wild-type protein. Such "hyperinhibited" mutants may provide useful tools for signaling studies that investigate the connections between SHP2 inhibition and the suppression of human disease progression.