Development of an efficient cell-based assay system for monitoring hepatitis C virus genotype 4a NS3/4A protease activity.

Background: Hepatitis C virus (HCV) represents a serious worldwide healthcare problem. No protective vaccines against HCV have been developed yet due to the fact that HCV is rapidly mutable, allowing the virus to escape from the neutralizing antibodies. Understanding of HCV was initially hampered by the inability to achieve viral replication in cell culture. Given its essential roles in viral polyprotein processing and immune evasion, HCV NS3/4A protease is a prime target for antiviral chemotherapy. We aimed to establish in vivo cell-based assay system for monitoring the activity of NS3/4A protease from HCV genotype 4a, the predominant genotype in Egypt, and the Middle East. Furthermore, the developed system was used to evaluate the inhibitory potency of a series of computer-designed chemically-synthesized compounds against NS3/4A protease from HCV genotype 4a.

Materials And Methods: Native as well as mutant cleavage sites to NS3/4A protease were cloned in frame into β-galactosidase gene of TA cloning vector. The target specificity of HCV NS3/4A was evaluated by coexpression of β-galactosidase containing the protease cleavage site with NS3/4A protease construct in bacterial cells. The activity of β-galactosidase was colorimetrically estimated in the cell lysate using orthonitro phenyl β-D-galactopyanoside (ONPG) as a substrate.

Results And Conclusions: We successfully developed an efficient cell-based system based on the blue/white selection of bacterial cells that are able to express functional/nonfunctional β-galactosidase enzyme.