A function essential to viral entry underlies the hepatitis B virus "a" determinant

Area of Science:

• Virology
• Molecular Biology
• Immunology

Background:

• Hepatitis B virus (HBV) entry relies on a pre-S1 domain receptor-binding site.
• A second infectivity determinant in the envelope protein's antigenic loop (AGL) was identified using hepatitis delta virus (HDV) as a surrogate.
• This AGL determinant's function is linked to cysteine residues crucial for the HBV
• a
• determinant.

Purpose of the Study:

• To precisely map the AGL infectivity determinant using alanine-scanning mutagenesis.
• To investigate the relationship between the AGL infectivity determinant and the HBV
• a
• determinant.
• To validate the role of AGL mutations in HBV infection.

Main Methods:

• Alanine-scanning mutagenesis to map the AGL infectivity determinant.
• Analysis of mutations' impact on viral infectivity and antigenicity.
• Introduction of HDV entry-deficient mutations into HBV virions.

Main Results:

• The AGL infectivity determinant was mapped to conserved residues interacting with cysteines in the disulfide bridge network.
• Some substitutions affected both infectivity and the "a" determinant; others selectively impacted infectivity.
• The G145R substitution, known to affect the "a" determinant, did not alter infectivity.
• Mutations rendering HDV entry-deficient also abrogated HBV infection.

Conclusions:

• The AGL infectivity determinant is closely related to, yet separable from, the HBV "a" determinant.
• A function has been assigned to the previously orphan "a" determinant.
• Characterizing AGL functions in viral entry may yield novel HBV antiviral strategies.