Structural and Functional Insights into HBx-Smc6 Targeting for HBV Inhibition

The hepatitis B virus (HBV) X protein (HBx) is a multifunctional regulator essential for HBV replication and HBV-associated hepatocarcinogenesis. Despite its central role, the molecular basis of HBx function has remained elusive. Here, we present the first cryo-electron microscopy structure of the human HBx-CRL4-Smc5/6 complex at 3.1 [A] resolution. In this reconstituted ten-subunit assembly, HBx adopts a Zn2 {square}-stabilized Y-shaped architecture that simultaneously engages the DDB1 and the Smc6 subunit. A composite helix-turn-helix (HTH) pocket in HBx accommodates a conserved "Leucine Key" motif (LRCKL) on Smc6, forming a critical interface essential for complex stability and function. Molecular docking and biochemical validation reveal that the compound Tranilast binds this HTH pocket, disrupts the HBx-Smc6 interaction, and suppresses HBV replication. These findings define the structural mechanism by which HBx counteracts host restriction and establish the HBx-Smc6 interface as a previously unrecognized and druggable target for antiviral intervention.