Purification and crystallization of NS5A domain I of hepatitis C virus

The NS5A protein of HCV is an essential component of the viral RNA replication machinery and may also function in modulation of the host cell environment. The exact function of NS5A in these processes remains unknown. NS5A is a large hydrophilic phosphoprotein protein consisting of three domains. The amino-terminal domain, designated domain I, coordinates a single zinc atom that is required for virus replication. We have determined the X-ray crystallographic structure of the domain I region of NS5A, and the structure sheds some light on the previously reported RNA binding activity observed for NS5A and suggests that the protein functions as a dimer. Here we describe the bacterial expression, purification, crystallization, and structural determination of the amino-terminal domain I of NS5A. The methods described herein should be of use for the generation of domain I for biochemical studies as well as future crystallization studies as antiviral compounds directed against this region of NS5A become available.