| This thesis reports the atomic structure of the Hepatitis E virus (HEV) in the form of a virus-like particle (VLP). HEV is a small, non-enveloped RNA virus in the family Hepeviridae and is the principal cause of endemic and epidemic acute viral hepatitis in developing countries. HEV contains three Open Reading Frames (ORFs), among which ORF2 encodes the capsid protein (amino acid 1-660), which plays a major role in virus assembly, viral cell entry, and host immune response.;Originally purified as a dimer, the truncated capsid protein (amino acid 112-608) self-assembles into a subviral particle during crystallization. Such a VLP, though smaller than its native counterpart, retains native-like immunogenicity and is a promising candidate for vaccine. With a 14-A cryo-electron microscopy (EM) reconstruction as the initial phasing model, we have solved the crystal structure of the HEV VLP to 3.5 A resolution using X-ray crystallography.;This high-resolution structure shows that each capsid protein contains three linear domains that form distinct structural elements: S, the continuous capsid shell; P1, the 3-fold protrusions; and P2, the 2-fold spikes. The S domain adopts a jelly-roll beta-barrel fold commonly observed in small RNA viruses. The P1 and P2 domains both adopt beta-barrel folds Each of these two domains possesses a potential polysaccharide binding site that may function in cell-receptor binding. Particularly, sugar binding to P1 at the capsid protein interface may lead to capsid disassembly and facilitate cell entry. The subviral particle structure allows us to postulate a possible pathway for the assembly of HEV. Further structural modeling, mimicking the native virus, indicates that the native T=3 capsid contains flat dimers, with less curvature than those of the T=1 VLP. Our findings significantly advance the understanding of HEV molecular biology and have applications to the development of vaccines and antiviral medications. |
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