Phosphorylation of the Arginine-Rich C-Terminal Domains of the Hepatitis B Virus (HBV) Core Protein as a Fine Regulator of the Interaction between HBc and Nucleic Acid

Abstract

<jats:p>The morphogenesis of Hepatitis B Virus (HBV) viral particles is nucleated by the oligomerization of HBc protein molecules, resulting in the formation of an icosahedral capsid shell containing the replication-competent nucleoprotein complex made of the viral polymerase and the pre-genomic RNA (pgRNA). HBc is a phospho-protein containing two distinct domains acting together throughout the viral replication cycle. The N-terminal domain, (residues 1–140), shown to self-assemble, is linked by a short flexible domain to the basic C-terminal domain (residues 150–183) that interacts with nucleic acids (NAs). In addition, the C-terminal domain contains a series of phospho-acceptor residues that undergo partial phosphorylation and de-phosphorylation during virus replication. This highly dynamic process governs the homeostatic charge that is essential for capsid stability, pgRNA packaging and to expose the C-terminal domain at the surface of the particles for cell trafficking. In this review, we discuss the roles of the N-terminal and C-terminal domains of HBc protein during HBV morphogenesis, focusing on how the C-terminal domain phosphorylation dynamics regulate its interaction with nucleic acids throughout the assembly and maturation of HBV particles.</jats:p>

Early Steps of Hepatitis B Life Cycle: From Capsid Nuclear Import to cccDNA Formation

“…However, this functional separation of HBc is over simplified, as different studies have shown that NTD plays a role in DNA synthesis and, conversely, CTD participates in capsid assembly [ 32 , 33 ]. CTD is highly basic and undergoes dynamic phosphorylation and dephosphorylation, which regulate many HBc functions including pgRNA encapsidation, reverse transcription, capsid stability, and intracellular trafficking [ 34 , 35 , 36 , 37 ].…”

“…In the first model, HBV capsids are believed to be responsible for NPC docking and genome delivery. Indeed, the CTD region, which is highly conserved between all genotypes, contains nuclear localization signal (NLS) sequences that have been shown to be functional when using NLS defective SV40 large T antigen as a reporter for subcellular localization or by studying the impact of mutations on HBc subcellular localization [ 35 , 43 , 44 ]. The role of these sequences in nuclear trafficking was further confirmed in the context of an assembled capsid by performing competition experiments for NPCs binding with peptides corresponding to NLS, using digitonin-permeabilized cells, or by studying capsid subcellular localization in hepatoma cells cotransfected with a vector coding HBc containing mutations in the putative NLS and viral polymerase [ 43 , 44 , 45 ].…”

Conformational Plasticity of Hepatitis B Core Protein Spikes Promotes Peptide Binding Independent of the Secretion Phenotype

“…The N -terminal domain of HBc is mainly α-helical and assembles into dimers, which form protruding spikes at the capsid surface [ 10 , 11 , 12 ]. The C -terminal domain is largely disordered and contains several phosphorylation sites [ 13 ] and an arginine-rich domain (ARD) that together regulate genome interaction (reviewed in [ 14 ]). The capsid accommodates the viral polymerase and a viral, partially double-stranded DNA genome of 3.2 kb.…”

Review article: immunisation against hepatitis B virus infection and the prevention of hepatocellular carcinoma

“…The nucleocapsid migrates towards the nucleus thanks to nuclear localisation signals carried by the HBc antigen. Through interactions with nuclear transport receptors and adaptor proteins of the nuclear pore complex, the capsids eventually disintegrate permitting the release of both core capsid subunits and of the relaxed circular HBV DNA (rcDNA) genome 13 . HBV DNA then enters the nucleus.…”