Uch37 is a de-ubiquitinating enzyme that is activated by Rpn13 and involved in the proteasomal degradation of proteins. The full-length Uch37 was shown to exhibit low iso-peptidase activity and is thought to be auto-inhibited. Structural comparisons revealed that within a homo-dimer of Uch37, each of the catalytic domains was blocking the other's ubiquitin (Ub)-binding site. This blockage likely prevented Ub from entering the active site of Uch37 and might form the basis of auto-inhibition. To understand the mode of auto-inhibition clearly and shed light on the activation mechanism of Uch37 by Rpn13, we investigated the Uch37-Rpn13 complex using a combination of mutagenesis, biochemical, NMR, and small-angle X-ray scattering (SAXS) techniques. Our results also proved that Uch37 oligomerized in solution and had very low activity against the fluorogenic substrate ubiquitin-7-amino-4-methylcoumarin (Ub-AMC) of de-ubiquitinating enzymes. Uch37Δ(Hb,Hc,KEKE), a truncation removal of the C-terminal extension region (residues 256-329) converted oligomeric Uch37 into a monomeric form that exhibited iso-peptidase activity comparable to that of a truncation-containing the Uch37 catalytic domain only. We also demonstrated that Rpn13C (Rpn13 residues 270-407) could disrupt the oligomerization of Uch37 by sequestering Uch37 and forming a Uch37-Rpn13 complex. Uch37 was activated in such a complex, exhibiting 12-fold-higher activity than Uch37 alone. Time-resolved SAXS (TR-SAXS) and FRET experiments supported the proposed mode of auto-inhibition and the activation mechanism of Uch37 by Rpn13. Rpn13 activated Uch37 by forming a 1:1 stoichiometric complex in which the active site of Uch37 was accessible to Ub.
Binding Sites ; Catalytic Domain ; Chromatography, Gel ; Crystallography, X-Ray ; Humans ; Membrane Glycoproteins ; chemistry ; genetics ; metabolism ; Nuclear Magnetic Resonance, Biomolecular ; Protein Binding ; Protein Conformation ; Protein Multimerization ; Scattering, Small Angle ; Ubiquitin Thiolesterase ; chemistry ; genetics ; metabolism ; Ultracentrifugation

OBJECTIVE: To investigate the effect of extracts with water and alcohol from Radix Trichosanthis on the cell survival and the expression of hepatitis B surface antigen (HBsAg) and hepatitis B e-antigen (HBeAg) in HepG2.2.15 cell supernatant. METHODS: The cell survival rate of HepG2.2.15 cells was detected by MTT assay. The HBsAg and HBeAg in HepG 2.2.15 cell supernatant were evaluated by enzyme linked immunosorbent assay. RESULTS: The water and alcohol soluble extracts from Radix Trichosanthis significantly inhibited the levels of HBsAg and HBeAg in HepG2.2.15 cells in a time-and-concentration-dependent manner. However, the therapeutic index of extracts with water from Radix Trichosanthis was better than that in the alcohol group. CONCLUSION The activity of water-soluble extract from Radix Trichosanthis is stronger on anti-hepatitis B virus than that of the alcohol-soluble extract.
Antiviral Agents ; pharmacology ; Drugs, Chinese Herbal ; classification ; pharmacology ; Hep G2 Cells ; Hepatitis B Surface Antigens ; biosynthesis ; Hepatitis B e Antigens ; biosynthesis ; Hepatitis B virus ; drug effects ; Humans