Hepatitis delta virus antigen forms dimers and multimeric complexes in vivo

Area of Science:

• Virology
• Molecular Biology
• Protein Biochemistry

Background:

• Hepatitis delta virus (HDV) replication involves a single open reading frame encoding hepatitis delta antigen (HDAg).
• HDAg exists in two forms, p24 delta and p27 delta, determined by translation termination.
• Understanding HDAg interactions is key to elucidating HDV replication mechanisms.

Purpose of the Study:

• To investigate the in vivo complex formation of hepatitis delta antigen (HDAg) species.
• To characterize the structure and stability of HDAg multimers.
• To identify potential protein interaction domains within HDAg.

Main Methods:

• Antibody precipitation assays to detect HDAg complexes.
• Glutaraldehyde cross-linking to stabilize protein interactions.
• Sucrose density gradient centrifugation to analyze HDAg multimer size.
• RNase digestion and SDS-PAGE to assess complex composition and monomeric forms.

Main Results:

• p27 delta and p24 delta form heterologous complexes in infected liver.
• HDV antigen (HDAg) exists as dimers and stable 15S multimers in vivo.
• 15S multimers dissociate into monomers upon denaturation, indicating non-covalent interactions.
• A specific N-terminal fragment of HDAg retains dimer formation capability, suggesting a role for residues 27-58.

Conclusions:

• Hepatitis delta antigen (HDAg) self-associates into dimers and multimers, essential for its function.
• The N-terminal region of HDAg, potentially via a coiled-coil motif, mediates these protein-protein interactions.
• These findings provide insights into the structural biology of HDAg during HDV infection.