Fusion protein corresponding to the serine protease NS3 (a.a. 3-181) and cofactor NS4A (a.a. 21-32) from Hepatitis C virus genotype 1a (HCV1a), GenBank Accession No. NC_004102, with Asp-to- Glu mutation on a.a. 168, and N-terminal FLAG-His tag, MW = 22.4 kDa, expressed in an E. coli expression system.