Structural and antigenic variation in Hepatitis B virus oncogene, HBx

Hepatitis B Virus (HBV) is a known oncogenic virus, with over 50% of infections leading to hepatocellular carcinoma. The virus's primary oncogenic protein is identified as HBx. Over the past decade, only a limited number of studies have explored the structure of HBx using computational approaches. Depending on the method used, two significantly different topologies with notable variations in secondary structure elements have been predicted for this protein. In this study, we compare both predicted structural configurations of HBx and extend our analysis across different genotypes and strains of both human and non-human HBV. Phylogenetic analysis of HBx suggests zoonotic transmission of the virus between humans and orangutan HBV. Several critical residues essential for HBV transcription, including Cys61, Cys69, Cys137, and His139, are conserved across all mammalian HBV, including human strains. In contrast, residues such as Ser25 (involved in intranuclear localization of HBx), Pro90 (associated with UVDBB interaction), and Cys115 (linked to mitochondrial localization of HBx) are exclusive to human HBV, indicating potential sub-neofunctionalization of the HBx protein in human strains. Molecular models of HBx generated using I-TASSER and AlphaFold were non-superimposable. Structural alignment with a partially resolved HBx structure, along with molecular dynamics (MD) simulations, supports the prediction made by AlphaFold. Additionally, AlphaFold predicted HBx structure exhibits similarity to palmitoleoyl transferases, suggesting a possible evolutionary origin. This study provides valuable insights into the origin and evolutionary development of the oncogenic potential of HBx in mammalian HBV.