Molecular Mechanism of Capsid Disassembly in Hepatitis B Virus

The disassembly of a viral capsid leading to the release of its genetic material into the host cell is a fundamental step in viral infection. Hepatitis B virus (HBV) in particular consists of identical capsid protein monomers that dimerize and also arrange themselves into pentamers or hexamers on the capsid surface. By applying atomistic molecular dynamics simulation to an entire solvated HBV capsid subject to a uniform mechanical stress protocol, we monitor the disassembly process down to the level of individual amino acids. The strain of an external force combined with thermal fluctuations causes structurally heterogeneous cracks to appear in the HBV capsid. Unlike the expectation from purely mechanical considerations, the cracks mainly occur within and between hexameric sites, whereas pentameric sites remain largely intact. Only a small subset of the capsid protein monomers governs disassembly. These monomers are distributed across the whole capsid, but belong to regions with a high degree of collective motion that we label communities. Cross-talk within these communities is a mechanism of crack propagation leading to destabilization of the entire capsid, and eventually its disassembly. We identify specific residues whose interactions are most readily lost during disassembly: R127, I139, Y132, N136, A137, and V149 are among the hotspots at the interfaces between dimers that lie within or span hexamers, leading to dissociation. The majority of these hotspots are evolutionary conserved, indicating that they are important for disassembly by avoiding over-stabilization of capsids. SignificanceHepatitis B virus (HBV) is a DNA virus that is 100 times more infectious than HIV. Despite the availability of a vaccine, the chronic infection rate of this virus is still about 300 million people globally. HBV chronic infection, for which no cure is currently available, can lead to liver cancer. Therefore, there is an unmet need to investigate the infection cycle of the virus. One of the most crucial steps in virus replication cycle is the release of its genetic material to the nucleus. During this step, the viral capsid enclosing the genetic material disassembles. However, its mechanism is unknown. Here, we utilize molecular simulations to shed light on the events leading to the capsid disassembly with atomistic detail.