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 (GenBank Accession No. NC_004102) with Asp-to-Val mutation on a.a. 168, an N-terminal FLAG-His tag, and a 4 a.a. linker, MW = 22.4 kDa, expressed in an E. coli expression system.