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

Chronic infection with hepatitis B virus (HBV) remains a global health issue, leading to liver diseases such as chronic hepatitis B, cirrhosis, and hepatocellular carcinoma. The HBV X protein (HBx) promotes viral replication and disease progression by interacting with various host proteins. One of its functions involves binding to microtubule-associated protein 1 light chain 3B (LC3B), which mediates selective autophagy and facilitates the removal of the immune-related protein TNFRSF10B (tumor necrosis factor receptor superfamily 10B). However, even the mechanism by which HBx interacts with LC3B remained unclear. In this study, we focused on the HBx-LC3B interaction as a first step and identified a conserved LC3-interacting region motif (Trp120-X-X-Leu123) within the Bcl-2 homology 3 (BH3)-like domain of HBx that directly binds to LC3B. This interaction was characterized using isothermal titration calorimetry and nuclear magnetic resonance (NMR) spectroscopy. We present the first NMR structure of LC3B in complex with the HBx BH3-like peptide, revealing that it adopts an extended conformation upon binding and that Trp120 and Leu123 are essential for LC3B recognition. Notably, the same portion forms an α-helix when binding to B-cell lymphoma 2 (Bcl-2) and B-cell lymphoma extra-large (Bcl-xL), suggesting that HBx uses different conformations to interact with distinct targets. This structural plasticity may underlie the multifunctional roles of HBx.