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Updated: Jun 25, 2026
Assessing Cellular Target Engagement by SHP2 (PTPN11) Phosphatase Inhibitors
Published on: July 17, 2020
Structural and functional characterization of the 2H-phosphatase domain of Sts-2 reveals an acid-dependent
Yunting Chen1, Jean Jakoncic, Nick Carpino
1Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York 11794-8661, USA.
Abstract:
The suppressors of T cell receptor (TCR) signaling 1 and 2 (Sts-1 and -2, respectively) are multidomain proteins that negatively regulate the signaling of membrane-bound receptors, including TCR and the epidermal growth factor receptor (EGFR). Sts-1 was recently shown to be a new type of protein tyrosine phosphatase (PTP), with the phosphatase activity located within its C-terminal phosphoglycerate mutase (PGM) homology domain and key for the regulation of TCR signaling in T cells. The activity of the related Sts-2 enzyme is significantly less than that of Sts-1. Here we investigate the phosphatase activity of the PGM domain of Sts-2, Sts-2(PGM). The crystal structure of Sts-2(PGM) is remarkably similar to Sts-1(PGM), including conservation of all catalytic residues. Insight into mechanistic details is provided by the structures of the apo, tungstate-bound, and phosphate-bound enzyme. The active site shows stringent specificity, with the k(cat) optimum at pH 5.0 suggesting that Sts-2 might function as an acid-dependent phosphatase. Mutation of active site residues Gln372, Ala446, Glu481, Ser552, and Ser582 to their equivalents in Sts-1 increases the phosphatase activity of Sts-2(PGM) toward model substrates. Overall, our data demonstrate that Sts-2(PGM) adopts the conformation of an active phosphatase whose activity is fundamentally different from that of Sts-1 despite the strong structural homology. They also demonstrate that nonconserved active site residues are responsible for the difference in activity between the two isoforms. These differences reflect possible distinct physiological substrates.
Insights
Suppressors of T cell receptor (TCR) signaling 1 and 2 (Sts-1 and Sts-2) are phosphatases. Despite structural similarity, Sts-2 has lower activity than Sts-1 due to nonconserved active site residues, suggesting distinct physiological roles.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Signaling
Background:
- Suppressors of T cell receptor (TCR) signaling (Sts-1 and -2) are negative regulators of receptor signaling.
- Sts-1 functions as a protein tyrosine phosphatase (PTP) via its C-terminal phosphoglycerate mutase (PGM) domain, crucial for T cell signaling.
- Sts-2 exhibits significantly lower enzymatic activity compared to Sts-1.
Purpose of the Study:
- To investigate the phosphatase activity of the Sts-2 PGM domain (Sts-2(PGM)).
- To elucidate the structural and mechanistic basis for the differing activities of Sts-1 and Sts-2.
- To identify key residues responsible for the distinct phosphatase activities between Sts-1 and Sts-2.
Main Methods:
- X-ray crystallography to determine the structure of Sts-2(PGM) in apo, tungstate-bound, and phosphate-bound states.
- Enzyme kinetics to assess the catalytic activity and pH optimum of Sts-2(PGM).
- Site-directed mutagenesis to alter Sts-2(PGM) active site residues to their Sts-1 counterparts.
Main Results:
- The crystal structure of Sts-2(PGM) closely resembles Sts-1(PGM), with conserved catalytic residues.
- Sts-2(PGM) exhibits optimal activity at pH 5.0, indicating potential acid-dependent function.
- Mutating specific active site residues in Sts-2(PGM) to their Sts-1 equivalents significantly enhanced its phosphatase activity.
Conclusions:
- Sts-2(PGM) possesses the active conformation of a phosphatase, but its activity differs fundamentally from Sts-1.
- Nonconserved active site residues are critical determinants of the distinct enzymatic activities between Sts-1 and Sts-2.
- These activity differences suggest that Sts-1 and Sts-2 may target distinct physiological substrates, implying specialized roles in cellular regulation.
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