Expression, Purification and Structural Characterization of Up-Regulated Gene 7 Encoded Protein

Up-Regulated Gene 7 (URG7) is a host gene up-regulated in HBV infected hepatocytes that has been suggested to have an anti-apoptotic activity mediated by caspases 3 and 8 and an endoplasmic reticulum localization. Here we report the structural characterization of the encoded protein URG7 by circular dichroism and fluorescence spectroscopy in different solvent media: phosphate buffer and two membrane-mimetic solvents, i.e. 2,2,2-trifluoroethanol (TFE) and SDS micelles. In all solvents URG7 contains substantial amounts of secondary structures. To obtain information about the structural organization and stability of URG7, its thermal denaturation in a membrane environment was studied and intermediate states of thermal unfolding were observed. Furthermore, fluorescence results in SDS micelles could be compatible with different environments for the four tryptophan residues in URG7. Preliminary NMR data indicate that URG7 in TFE solution is quite flexible and not well folded. These data are the first structural information on URG7 and might provide an insight into its structure-function relationships.