The 1.35 Å resolution structure of the phosphatase domain of the suppressor of T‐cell receptor signaling protein in complex with sulfate
The suppressor of T‐cell signaling (Sts) proteins are multidomain proteins that negatively regulate the signaling of membrane‐bound receptors, including the T‐cell receptor (TCR) and the epidermal growth‐factor receptor (EGFR). They contain at their C‐terminus a 2H‐phosphatase homology (PGM) domain that is responsible for their protein tyrosine phosphatase activity. Here, the crystal structure of the phosphatase domain of Sts‐1, Sts‐1PGM, was determined at pH 4.6. The asymmetric unit contains two independent molecules and each active site is occupied by a sulfate ion. Each sulfate is located at the phosphate‐binding site and makes similar interactions with the catalytic residues. The structure suggests an explanation for the lower Michaelis–Menten constants at acidic pH.
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