Efficient cleavage by signal peptide peptidase requires residues within the signal peptide between the core and E1 proteins of hepatitis C virus strain J1

This study resolves a discrepancy in hepatitis C virus (HCV) research regarding which amino acids are essential for signal peptide peptidase (SPP) cleavage of the viral core protein. The authors demonstrate that amino acids Ala180, Ser183, and Cys184 within the signal peptide between core and E1 proteins are necessary for efficient SPP processing in HCV strain J1, contrary to a previous report. The key finding is that the earlier conflicting conclusion resulted from technical limitations in gel electrophoresis using standard Tris/glycine buffers, which failed to adequately separate wild-type core from mutant core proteins. Using alternative Tris/Bicine buffer systems and SPP inhibitor experiments, the researchers showed that mutations at these three positions prevent SPP cleavage, leaving core retained at the endoplasmic reticulum membrane rather than trafficking to lipid droplets. These findings align with previously established requirements for strain Glasgow and demonstrate that these amino acid positions are highly conserved across HCV sequences, suggesting they play a fundamental role in SPP-mediated core maturation across all HCV strains.

Key findings

• Amino acids Ala180, Ser183, and Cys184 in the core-E1 signal peptide are essential for efficient SPP cleavage in HCV strain J1, contradicting a previous study
• Previous conflicting results were due to inadequate separation of wild-type and mutant core proteins on standard polyacrylamide gels; Tris/Bicine buffer systems effectively distinguished these forms
• Mutations preventing SPP cleavage cause core protein to remain at the endoplasmic reticulum membrane instead of trafficking to lipid droplets
• These critical amino acids are invariant across 85% of HCV sequences in public databases, indicating fundamental importance for core maturation across all HCV strains