Molecular basis of the interaction of the human tyrosine phosphatase PTPN3 with the hepatitis B virus core protein.

Interactions between the hepatitis B virus core protein (HBc) and host cell proteins are poorly understood, although they may be essential for the propagation of the virus and its pathogenicity. HBc has a C-terminal PDZ (PSD-95, Dlg1, ZO-1)-binding motif (PBM) that is responsible for interactions with host PDZ domain-containing proteins. In this work, we focused on the human protein tyrosine phosphatase non-receptor type 3 (PTPN3) and its interaction with HBc. We solved the crystal structure of the PDZ domain of PTPN3 in complex with the PBM of HBc, revealing a network of interactions specific to class I PDZ domains despite the presence of a C-terminal cysteine in this atypical PBM. We further showed that PTPN3 binds the HBc protein within capsids or as a homodimer. We demonstrate that overexpression of PTPN3 significantly affects HBV infection in HepG2 NTCP cells. Finally, we performed proteomics studies on both sides by pull-down assays and screening of a human PDZ domain library. We identified a pool of human PBM-containing proteins that might interact with PTPN3 in cells and that could be in competition with the HBc PBM during infection, and we also identified potential cellular partners of HBc through PDZ-PBM interactions. This study opens up many avenues of future investigations into the pathophysiology of HBV.

Structural and functional characterization of the PDZ domain of the human phosphatase PTPN3 and its interaction with the human papillomavirus E6 oncoprotein.

The human protein tyrosine phosphatase non-receptor type 3 (PTPN3) is a PDZ (PSD-95/Dlg/ZO-1) domain-containing phosphatase with a tumor-suppressive or a tumor-promoting role in many cancers. Interestingly, the high-risk genital human papillomavirus (HPV) types 16 and 18 target the PDZ domain of PTPN3. The presence of a PDZ binding motif (PBM) on E6 confers interaction with a number of different cellular PDZ domain-containing proteins and is a marker of high oncogenic potential. Here, we report the molecular basis of interaction between the PDZ domain of PTPN3 and the PBM of the HPV E6 protein. We combined biophysical, NMR and X-ray experiments to investigate the structural and functional properties of the PDZ domain of PTPN3. We showed that the C-terminal sequences from viral proteins encompassing a PBM interact with PTPN3-PDZ with similar affinities to the endogenous PTPN3 ligand MAP kinase p38γ. PBM binding stabilizes the PDZ domain of PTPN3. We solved the X-ray structure of the PDZ domain of PTPN3 in complex with the PBM of the HPV E6 protein. The crystal structure and the NMR chemical shift mapping of the PTPN3-PDZ/peptide complex allowed us to pinpoint the main structural determinants of recognition of the C-terminal sequence of the E6 protein and the long-range perturbations induced upon PBM binding.

The molecular basis for the substrate specificity of protein tyrosine phosphatase PTPN3.

In this issue of Structure, Chen et al. present structures of the FERM-containing protein tyrosine phosphatase PTPN3 in complex with a phosphopeptide fragment of substrate epidermal growth factor receptor pathway substrate, providing detailed information on substrate specificity.

Substrate specificity and plasticity of FERM-containing protein tyrosine phosphatases.

Epidermal growth factor receptor (EGFR) pathway substrate 15 (Eps15) is a newly identified substrate for protein tyrosine phosphatase N3 (PTPN3), which belongs to the FERM-containing PTP subfamily comprising five members including PTPN3, N4, N13, N14, and N21. We solved the crystal structures of the PTPN3-Eps15 phosphopeptide complex and found that His812 of PTPN3 and Pro850 of Eps15 are responsible for the specific interaction between them. We defined the critical role of the additional residue Tyr676 of PTPN3, which is replaced by Ile939 in PTPN14, in recognition of tyrosine phosphorylated Eps15. The WPD loop necessary for catalysis is present in all members but not PTPN21. We identified that Glu instead of Asp in the WPE loop contributes to the catalytic incapability of PTPN21 due to an extended distance beyond protonation targeting a phosphotyrosine substrate. Together with in vivo validations, our results provide novel insights into the substrate specificity and plasticity of FERM-containing PTPs.

Reciprocal allosteric regulation of p38γ and PTPN3 involves a PDZ domain-modulated complex formation.

The mitogen-activated protein kinase p38γ (also known as MAPK12) and its specific phosphatase PTPN3 (also known as PTPH1) cooperate to promote Ras-induced oncogenesis. We determined the architecture of the PTPN3-p38γ complex by a hybrid method combining x-ray crystallography, small-angle x-ray scattering, and chemical cross-linking coupled to mass spectrometry. A unique feature of the glutamic acid-containing loop (E-loop) of the phosphatase domain defined the substrate specificity of PTPN3 toward fully activated p38γ. The solution structure revealed the formation of an active-state complex between p38γ and the phosphatase domain of PTPN3. The PDZ domain of PTPN3 stabilized the active-state complex through an interaction with the PDZ-binding motif of p38γ. This interaction alleviated autoinhibition of PTPN3, enabling efficient tyrosine dephosphorylation of p38γ. Our findings may enable structure-based drug design targeting the PTPN3-p38γ interaction as an anticancer therapeutic.

Protein-tyrosine phosphatase H1 controls growth hormone receptor signaling and systemic growth.

Several protein-tyrosine phosphatases (PTPs) have been implicated in the control of growth hormone receptor (GHR) signaling, but none have been shown to affect growth in vivo. We have applied a battery of molecular and cellular approaches to test a family-wide panel of PTPs for interference with GHR signaling. Among the subset of PTPs that showed activity in multiple readouts, we selected PTP-H1/PTPN3 for further in vivo studies and found that mice lacking the PTP-H1 catalytic domain show significantly enhanced growth over their wild type littermates. In addition, PTP-H1 mutant animals had enhanced plasma and liver mRNA expression of insulin-like growth factor 1, as well as increased bone density and mineral content. These observations point to a controlling role for PTP-H1 in modulating GHR signaling and systemic growth through insulin-like growth factor 1 secretion.