HCV Microbiology

HCV replicates mainly in the hepatocytes of the liver, where it is estimated that daily each infected cell produces approximately fifty virions with a calculated total of one trillion virions generated.

The virus may also replicate in peripheral blood mononuclear (PBMC) cells, potentially accounting for the high levels of immunological disorders found in chronically infected HCV patients.

HCV mutates rapidly due to a high error rate on the part of the virus’ RNA-dependent RNA polymerase. The mutation rate produces so many variants of the virus it is considered a quasispecies rather than a conventional virus species.

Once inside the hepatocyte, HCV takes over portions of the intracellular machinery to replicate. The HCV genome is translated to produce a single protein of around 3011 amino acids. The polyprotein is subsequently processed by viral and host proteases to produce three structural (virion-associated) and seven nonstructural (NS) proteins.

The HCV core protein has 191 amino acids and can be divided into three domains on the basis of hydrophobicity. The N-terminal hydrophilic D1 domain, which consists of the first 117 amino acids, is mainly involved in RNA binding and oligomerization of the core protein; this core domain D1 interacts with the cellular DEAD-box RNA helicase DDX3

The NS proteins subsequently recruit the viral genome into an RNA replication complex, consisting of rearranged lipid droplet (LD) associated cytoplasmic membranes. The endoplasmic reticulum in particular are deformed into uniquely shaped membrane structures termed ‘membranous webs’. These structures can be induced by expression of the viral protein NS4B.

RNA replication takes places via the viral RNA-dependent RNA polymerase NS5B, which produces a negative strand RNA intermediate. The negative strand RNA then serves as a template for the production of new positive strand viral genomes. With the help of cytoplasmic host machinery, nascent genomes can then be translated, further replicated or packaged within new virus particles.

Expression of HCV core results in the redistribution of a proportion of DDX3 Helicases to the cytoplasmic LD associated replication complex, where it co-localizes with the viral core. It is during the translation phase of viral replication that DDX3 RNA Helicases, mobilised by the HCV core protein D1, play an essential part.