Structural basis of the hepatitis B virus X protein in complex with DDB1

Proc Natl Acad Sci U S A. 2025 Jun 17;122(24):e2421325122. doi: 10.1073/pnas.2421325122. Epub 2025 Jun 13.

Abstract

A cure for chronic hepatitis B requires eliminating or permanently silencing covalently closed circular DNA (cccDNA). A pivotal target of this approach is the hepatitis B virus (HBV) X protein (HBx), which is a key factor that promotes transcription from cccDNA. However, the HBx structure remains unsolved. Here, we present the cryoelectron microscopy structure of HBx in complex with DDB1, which is an essential complex for cccDNA transcription. In this structure, hydrophobic interactions within HBx were identified, and mutational analysis highlighted their importance in the HBV life cycle. Our biochemical analysis revealed that the HBx-DDB1 complex directly interacts simultaneously with NSE3, which is a component of the SMC5/6 complex, and Spindlin1. Additionally, HBx-DDB1 complex dynamics were explored via high-speed atomic force microscopy. These findings provide comprehensive insights into the structure and function of HBx in HBV replication.

Keywords: HBx; cryo-EM structure; hepatitis B virus; high-speed AFM.

MeSH terms

  • Cryoelectron Microscopy
  • DNA, Circular / genetics
  • DNA, Circular / metabolism
  • DNA, Viral / genetics
  • DNA, Viral / metabolism
  • DNA-Binding Proteins* / chemistry
  • DNA-Binding Proteins* / genetics
  • DNA-Binding Proteins* / metabolism
  • Hepatitis B virus* / genetics
  • Hepatitis B virus* / metabolism
  • Hepatitis B virus* / physiology
  • Humans
  • Microscopy, Atomic Force
  • Protein Binding
  • Trans-Activators* / chemistry
  • Trans-Activators* / genetics
  • Trans-Activators* / metabolism
  • Viral Regulatory and Accessory Proteins
  • Virus Replication

Substances

  • Viral Regulatory and Accessory Proteins
  • hepatitis B virus X protein
  • Trans-Activators
  • DDB1 protein, human
  • DNA-Binding Proteins
  • DNA, Viral
  • DNA, Circular