Abstract
Hepatitis B virus (HBV) production requires intricate interactions between the envelope and core proteins. Analyses of mutants of these proteins have made it possible to map regions involved in the formation and secretion of virions. Tests of binding between core and envelope peptides have also been performed in cell-free conditions, to study the interactions potentially underlying these mechanisms. We investigated the residues essential for core-envelope interaction in a cellular context in more detail, by transiently producing mutant or wild-type L, S, or core proteins separately or in combination, in Huh7 cells. The colocalization and interaction of these proteins were studied by confocal microscopy and co-immunoprecipitation, respectively. The L protein was shown to constitute a molecular platform for the recruitment of S and core proteins in a perinuclear environment. Several core amino acids were found to be essential for direct interaction with L, including residue Y132, known to be crucial for capsid formation, and residues L60, L95, K96 and I126. Our results confirm the key role of L in the tripartite core-S-L interaction and identify the residues involved in direct core-L interaction. This model may be valuable for studies of the potential of drugs to inhibit HBV core-envelope interaction.
Highlights
Hepatitis B virus (HBV) production requires intricate interactions between the envelope and core proteins
During the egress of HBV particles, the capsid shell formed in the cell is enclosed by the viral envelope, which is composed of cellular lipids and viral envelope proteins, in the endoplasmic reticulum[5,8,37]
The domains of the envelope and core proteins potentially required for capsid envelopment were mapped in previous molecular studies with mutants, in which virions secretion in the supernatant of transfected cells was used as the readout[18,26,38,39,40,41]
Summary
Hepatitis B virus (HBV) production requires intricate interactions between the envelope and core proteins. Several hypotheses have been proposed to explain the secretion of mature and empty particles, but not of immature particles These hypotheses include structural modifications of the core protein[4,9] and the presence of single-stranded (ss) DNA or pre-genomic (pg) RNA in assembled core constituting a signal blocking the envelopment of immature particles[5,6]. The three dimensional (3D) structures of www.nature.com/scientificreports the NTD and the full-length core have been determined by X-ray diffraction and cryoelectron microscopy[11,14,15] They contain five alpha helices, including the α3 and α4 helices forming a protuberance at the capsid surface, called the spike, which is involved in core dimerization. In its i-preS conformation, the preS1 region is involved in interactions with the capsid via a short conserved domain, the matrix domain (MD), which has been mapped to the preS1/preS2 junction[23,26,27]
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