Crystal structure of human TMDP, a testis-specific dual specificity protein phosphatase: Implications for substrate specificity

The testis- and skeletal-musclespecific dual-specificity phosphatase (TMDP) is a member of the dual-specificity phosphatase (DSP) subgroup of protein tyrosine phosphatases. TMDP has similar activities toward both tyrosine and threonine phosphorylated substrates, and is supposed to be involved in spermatogenesis. Here, we report the crystal structure of human TMDP at a resolution of 2.4 angstrom. In spite of high sequence similarity with other DSPs, the crystal structure of TMDP shows distinct structural motifs and surface properties. In TMDP, the alpha 1-beta 1. loop, a substrate recognition motif is located further away from the active site loop in comparison to prototype DSP Vaccinia HI related phophatase (VHR), which preferentially dephosphorylates tyrosine phosphorylated substrates and down-regulates MAP kinase signaling. Residues in the active site residues of TMDP are smaller in size and more hydrophobic than those of VHR. In addition, TMDP cannot be aligned with VHR in loop beta 3-alpha 4. These differences in the active site of TMDP result in a flat and wide pocket structure, allowing equal binding of phosphotyrosine and phosphothreonine substrates. Proteins 2007; 66:239-245. (c) 2006 Wiley-Liss, Inc.