Interactions between hepatitis delta virus proteins.

Area of Science:

• Virology
• Molecular Biology
• Structural Biology

Background:

• Hepatitis delta virus (HDV) delta antigens (deltaAg-S and deltaAg-L) have distinct roles in viral replication and assembly.
• A shared N-terminal region (aa 12-60) mediates protein-protein interactions essential for HDV lifecycle.
• Previous structural studies suggested coiled-coil dimer formation with potential for tetramerization.

Purpose of the Study:

• To investigate if in vitro structural predictions of delta antigen multimerization apply to full-length proteins in vivo.
• To determine the role of conserved amino acids in delta antigen protein-protein interactions and biological functions.

Main Methods:

• Site-directed mutagenesis of nine conserved amino acids to alanine in both deltaAg-S and deltaAg-L.
• In vivo assessment of mutant deltaAg-S ability to support HDV genome replication.
• In vivo evaluation of mutant deltaAg-L as dominant-negative inhibitors of HDV replication.

Main Results:

• Mutations in conserved amino acids significantly affected the in vivo functions of both deltaAg-S and deltaAg-L.
• The observed effects of mutations correlated with the predicted hierarchy of importance for multimerization.
• DeltaAg-S supported HDV replication, while deltaAg-L inhibited it, with both activities modulated by the mutations.

Conclusions:

• Ordered protein-protein interactions mediated by the N-terminal region are critical for delta antigen biological activities.
• In vivo functions of delta antigens in HDV replication and assembly depend on their multimerization status.
• Structural predictions of peptide interactions can be extrapolated to full-length proteins in a biological context.