Structural determinant of human La protein critical for internal initiation of translation of hepatitis C virus RNA

Abstract

Human La protein has been implicated to facilitate internal ribosome entry site (IRES) mediated translation of hepatitis C virus (HCV). Earlier, we have demonstrated that RNA recognition motif (RRM) encompassing 112-184 residues of La protein interacts with HCV-IRES near initiator AUG. A synthetic peptide LaR2C (24mer), derived from La-RRM (112-184), retained RNA binding ability, competes with the La protein binding to HCV IRES and inhibits translation. The peptide interferes with the assembly of 48S complexes resulting in the accumulation of pre-initiation complexes that are incompetent for the 60S ribosomal subunit joining. Here, NMR spectroscopy of the HCV-IRES bound peptide complex revealed putative contact points, mutations at which showed reduced RNA binding and translation inhibitory activity. The residues responsible for RNA recognition were found to form a turn in the RRM (112-184) structure. A 7-mer peptide comprising this turn showed significant translation inhibitory activity. The bound structure of the peptide inferred from transferred NOE experiments suggests it to be a β-turn. This conformation is significantly different from that observed in free RRM (112-184) NMR structure suggesting paths towards a better stabilized mimetic. Interestingly, addition of hexa-arginine tag enabled the peptide to enter Huh7 cells and showed inhibition HCV-IRES function. More importantly, the peptide significantly inhibited replication of HCV monocistronic replicon. Elucidation of the structural determinant of the peptide provides basis for developing small peptidomimetic as potent anti-HCV therapeutics.