Structural insights into the interaction between the BH3-like domain of hepatitis B virus X protein and LC3B

Area of Science:

• Biochemistry
• Molecular Biology
• Virology

Background:

• Chronic hepatitis B virus (HBV) infection is a global health concern, leading to severe liver diseases.
• The HBV X protein (HBx) drives viral replication and disease progression through host protein interactions.
• HBx interacts with LC3B, a key mediator of selective autophagy, to regulate immune protein removal.

Purpose of the Study:

• To elucidate the molecular mechanism of the HBx-LC3B interaction.
• To identify the specific binding region and structural basis of this interaction.

Main Methods:

• Isothermal titration calorimetry (ITC) to quantify binding.
• Nuclear magnetic resonance (NMR) spectroscopy to determine the structure of the complex.
• Site-directed mutagenesis to assess the role of specific residues.

Main Results:

• Identified a conserved LC3-interacting region (LIR) motif (Trp120-X-X-Leu123) in the HBx BH3-like domain that directly binds LC3B.
• Determined the first NMR structure of LC3B complexed with an HBx peptide, showing an extended conformation.
• Confirmed Trp120 and Leu123 are essential for LC3B recognition.
• Observed that the HBx peptide adopts an α-helical conformation when binding to Bcl-2 and Bcl-xL, contrasting with its LC3B-bound state.

Conclusions:

• The HBx-LC3B interaction is mediated by a specific LIR motif within the HBx BH3-like domain.
• HBx exhibits structural plasticity, adopting different conformations to bind distinct host proteins like LC3B, Bcl-2, and Bcl-xL.
• This conformational flexibility likely contributes to the multifaceted roles of HBx in HBV pathogenesis.