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PDBsum entry 2ikq

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Signaling protein, immune system PDB id
2ikq
Jmol
Contents
Protein chains
262 a.a.
Ligands
PO4 ×3
Waters ×10

References listed in PDB file
Key reference
Title A phosphatase activity of sts-1 contributes to the suppression of tcr signaling.
Authors A.Mikhailik, B.Ford, J.Keller, Y.Chen, N.Nassar, N.Carpino.
Ref. Mol Cell, 2007, 27, 486-497. [DOI no: 10.1016/j.molcel.2007.06.015]
PubMed id 17679096
Abstract
Precise signaling by the T cell receptor (TCR) is crucial for a proper immune response. To ensure that T cells respond appropriately to antigenic stimuli, TCR signaling pathways are subject to multiple levels of regulation. Sts-1 negatively regulates signaling pathways downstream of the TCR by an unknown mechanism(s). Here, we demonstrate that Sts-1 is a phosphatase that can target the tyrosine kinase Zap-70 among other proteins. The X-ray structure of the Sts-1 C terminus reveals that it has homology to members of the phosphoglycerate mutase/acid phosphatase (PGM/AcP) family of enzymes, with residues known to be important for PGM/AcP catalytic activity conserved in nature and position in Sts-1. Point mutations that impair Sts-1 phosphatase activity in vitro also impair the ability of Sts-1 to regulate TCR signaling in T cells. These observations reveal a PGM/AcP-like enzyme activity involved in the control of antigen receptor signaling.
Figure 3.
Figure 3. Sts-1[PGM] Structure
(A) Ribbon diagram of dimeric Sts-1[PGM]. The side chains of His-380 and His-565 are shown as ball-and-stick representations to indicate the location of the active site. Prepared with Molscript (Kraulis, 1991) and PyMOL (http://pymol.sourceforge.net/).
(B) Secondary structure elements of the Sts-1[PGM] dimer.
Figure 4.
Figure 4. The Sts-1[PGM] Active Site
(A) Comparison of Sts-1[PGM] with E. coli PGM (ecPGM). Critical catalytic residues of ecPGM, and the homologous residues of Sts-1[PGM], are shown in gold ball-and-stick representation. The two regions that deviate between the two structures, Inserts 1 and 2 (Sts-1 residues 399–436 and 505–535), are in red and blue, respectively. The C termini are shown in green.
(B) Active site residues. Superposition of the known active site residues of ecPGM (cyan) with the homologous residues of Sts-1[PGM].
(C) Interactions made by Sts-1[PGM] active site residues with a phosphate ion. The omit map difference electron density of the phosphate is shown at 4 σ cutoff in black. The Sts-1[PGM] active site residues interacting with the phosphate molecule are shown in ball-and-stick representation. Dotted lines represent hydrogen bond interactions. Secondary structure elements are displayed in green.
(D) Mutation of Sts-1[PGM] active site residues renders Sts-1 catalytically inactive toward pNPP. Tagged wild-type or mutant proteins were expressed in 293T cells, precipitated, and evaluated for pNPP phosphatase activity. Error bars are as in Figure 1.
(E) Solvent accessibility of the Sts-1[PGM] active site. Surface representations of Sts-1[PGM] (left) and ecPGM (right) illustrate the different configurations of their respective catalytic pockets, with the active site cleft of Sts-1[PGM] broader and more exposed than that of ecPGM. Conserved basic and acidic residues that are visible are labeled and shown as blue and red patches.
(F) PGM domain activity is not regulated by the Sts-1 protein-protein interaction domains. The ΔUBA Sts-1 mutant lacks the UBA domain (residues 1–67), and the W284A point mutation renders the Sts-1 SH3 domain unable to bind its target sequences (Kowanetz et al., 2004). Proteins were expressed in 293T cells, immunoprecipitated with Flag antibodies, and evaluated for pNPP phosphatase activity relative to wild-type Sts-1. Each mutant was assayed in triplicate (error bars), and representative levels of precipitated proteins are displayed.
The above figures are reprinted from an Open Access publication published by Cell Press: Mol Cell (2007, 27, 486-497) copyright 2007.
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