A research team at Gilead Sciences recently determined the x-ray crystal structure of the Hepatitis C virus (HCV) RNA polymerase while assembled with the other components of the RNA replication machinery, as published in the study entitled “Structural basis for RNA replication by the hepatitis C virus polymerase” in the journal Science on Feb 19, 2015.
HCV infects more than 3% of the world’s population, and although frequently asymptomatic, a long-term HCV infection can lead to liver cancer and cirrhosis, making it a major cause of liver transplantation in the US.
HCV genetic material is packed in a single strand of RNA which is replicated by the viral NS5B RNA-dependent RNA polymerase once the virus enters hepatocytes. The virus then uses the intracellular machinery to replicate and it is estimated that 1.3 × 1012 virons (virus particles) are produced per day in each infected patient. As the active enzymatic site of this replication complex is highly conserved it is targetable by nucleotide analog inhibitors such as sofosbuvir, recently approved for chronic HCV treatment.
The elucidation of HCV RNA’s replication molecular details can lead to the discovery of more effective nucleotide-based drugs for HCV.
The research team, led Thomas Edwards, determined high resolution X-ray crystal structures of the HCV polymerase during the process of RNA replication, revealing molecular snap-shots of the process both at primed initiation and elongation states of RNA replication. “For the first time we can see at the atomic level how the HCV polymerase interacts with the genomic RNA template, replicating RNA, and nucleotide substrates,” said Edwards in a press release.
In addition, the structural data presented demonstrates how the HCV polymerase recognizes sofosbuvir in a manner distinct from either native substrates or other nucleotide-based inhibitors used in therapies.
“These structures advance our understanding of how an important member of the Flaviviridae family of viruses replicates genomic RNA,” said William Lee, Senior Vice President of Research at Gilead Sciences, further concluding that “this information will be useful in identifying replication inhibitors of other pathogenic viruses in this family responsible for human diseases.”