Hepatitis C Virus Non-structural Protein 3 (HCV NS3): A Multifunctional Antiviral Target

Abstract

Hepatitis C virus non-structural protein 3 contains a serine protease and an RNA helicase. Protease cleaves the genomeencoded polyprotein and inactivates cellular proteins required for innate immunity. Protease has emerged as an important target for the development of antiviral therapeutics, but drug resistance has turned out to be an obstacle in the clinic. Helicase is required for both genome replication and virus assembly. Mechanistic and structural studies of helicase have hurled this enzyme into a prominent position in the field of helicase enzymology. Nevertheless, studies of helicase as an antiviral target remain in their infancy. Hepatitis C virus (HCV)3 infection is a leading cause of chronic liver disease and hepatocellular carcinoma. HCV is the founding member of the Hepacivirus genus of the family Flaviviridae (1). The HCV genome is a single-stranded RNA of positive polarity that is on the order of 9000 nucleotides (nt) in length (Fig. 1a). The 5Ј-non-translated region (NTR) contains a terminal stem-loop that is a required cis-acting replication element and the internal ribosome entry site. The 3Ј-NTR contains a cis-acting replication element that consists of an RNA stem-loop of variable sequence, a polyuridine/polypyrimidine tract of variable length, and a highly conserved "X-tail. " The variability observed in the 3Ј-NTR and elsewhere in the genome is sufficient to permit classification of HCV into six distinct genotypes.The HCV genome encodes a single open reading frame, the translation of which is directed by the internal ribosome entry site. The HCV polyprotein is on the order of 3000 amino acids long and can be divided into a structural region (C-p7 proteins) and a non-structural (NS) region (NS2-NS5B proteins) (Fig. 1a). Cleavage of the HCV polyprotein occurs co-and posttranslationally by host (structural region) and viral (non-structural region) proteases. Only the NS3-NS5B region of the polyprotein is required for genome replication in cell culture (2). NS5B is the viral RNA-dependent RNA polymerase (3). NS5A is a phosphoprotein (4) capable of specifically interacting with the 3Ј-NTR of the HCV genome (5), other non-structural proteins (6), and numerous cellular proteins (7,8). NS5A also functions in virus assembly (9, 10). NS4B is an integral membrane protein that is required for assembly of the "membranous web," the organelle used for RNA replication (11,12). NS4A is a cofactor for NS3 that directs the localization of NS3 and modulates its enzymatic activities (13). The N-terminal one-third of NS3 contains the protease activity responsible for processing of the non-structural region of the polyprotein (Fig. 1b) (14 -16) and some cellular proteins (17-19). The C-terminal two-thirds of NS3 is an RNA helicase of the DExH family (Fig. 1c) (20). The biological function of the RNA helicase activity is not known but may include 1) RNA folding/remodeling (21), 2) enhancement of polymerase processivity (22), and/or 3) genome encapsidation (23).The significance, if any, of having the major viral p...

Hepatitis C virus in vitro replication is efficiently inhibited by acridone Fac4

“…Some acridones from Rutaceae plants showed great 153 antiviral activity against viruses with DNA genomes like herpes simplex virus serotypes 1 and 2 154 (HSV-1 and HSV-2), human cytomegalovirus (HCMV) and Epstein-Barr virus (Chansriniyom et 155 al., 2009;Itoigawa et al, 2003;Takemura et al, 1995;Yamamoto et al, 1989). For RNA 156 viruses, acridones presented activity against HIV-1, bovine viral diarrhea virus (BVDV), all 157 serotypes of dengue virus (DENV) and HCV, the last three belonging to the Flaviviridae family 158 (Fujiwara et al, 1999;Houe, 2003;Mazzucco et al, 2015;Raney et al, 2010;Sepulveda et al, 159 2008;Stankiewicz-Drogon et al, 2010;Stankiewicz-Drogon et al, 2008;Tabarrini et al, 2006;160 Turpin et al, 1998). 161 Our results showed that Fac4 inhibited up to 92% of HCV replication in the context of either the 162 subgenomic replicon or full length JFH1 HCVcc.…”

Exploring resistance pathways for first-generation NS3/4A protease inhibitors boceprevir and telaprevir using Bayesian network learning

“…Generations can be distinguished within the PI class based on binding properties with the catalytic triad of the NS3 protease (Salam and Akimitsu, 2013). The first-generation PIs are linear α-ketoamide compounds telaprevir and boceprevir, which covalently bind the enzyme and display only antiviral activity towards HCV genotype 1 (Raney et al, 2010). The second-generation PIs such as faldaprevir and simeprevir, bind the catalytic triad in a non-covalent manner, and show antiviral activity towards non-1 HCV genotypes too (De Luca et al, 2014).…”

Untitled

“…where Ser139, His57, and Asp81 in HCV NS3 form the catalytic triad of the enzyme ( Figure 2). The crystal structure and specificity of HCV protease have been characterized in detail [9][10][11]. Its catalytic triad has been found to be constituted of Ser139, His57, and Asp81 residues ( Figure 2).…”