DescriptionHepatitis C is a liver disease caused by hepatitis C virus (HCV). HCV is the major cause of cirrhosis and hepatocellular cancer in the US and is the number one cause of liver transplantation. An estimate of 3.5 million people is chronically infected in the US with 400,000 individuals deaths from chronic HCV infection every year. Several direct-acting antiviral (DAA) agents have been approved by the Food and Drug Administration (FDA). HCV is a blood-borne virus, which prior to 1992 was transmitted through blood transfusion. An estimated 41,200 new cases of HCV infection occurred in the US with an additional 1.75 million worldwide in 2016. Therefore, there is an urgent need to control the transmission of HCV, in addition to the antiviral intervention to limit the spread of the virus. Vaccination is the most effective way to control the infection rate as no infectious disease has ever been eradicated by treatment alone. However, no vaccine is available to prevent HCV infection.
A useful mammalian cell expression system was described to produce HCV envelope glycoproteins E1 and E2, as well as the cell surface receptors, scavenger receptor class B type I (SRB1) and cluster of differentiation 81 (CD81). Our method combines the speed and high efficiency of lentiviral infection with an adherent cell bioreactor to allow large-scale production of proteins in mammalian cell lines. The full-length ectodomain of HCV E1 was produced at milligram quantity and is recognized by conformational antibodies from patient samples. E1 can associate with the apolipoproteins from the cell culture serum. HCV E2 produced by the mammalian cell expression system has the function to bind cell surface receptors and antibodies. Crystals of E2 and CD81 diffract to 4.3 Å resolution allowing us to produce a low-resolution model of the E2-receptor complex.
Overall, our result extends the current understanding of HCV entry by providing more structural, biophysical, and functional information on the HCV glycoproteins. The studies of the receptor interaction can contribute to vaccine design to halt the spread of HCV infection.