Crystal Structure of the Human Astrovirus Capsid Protein

Abstract

Human astrovirus (HAstV) is a leading cause of viral diarrhea in infants and young children worldwide. HAstV is a nonenveloped virus with a T=3 capsid and a positive-sense RNA genome. The capsid protein (CP) of HAstV is synthesized as a 90-kDa precursor (VP90) that can be divided into three linear domains: a conserved N-terminal domain, a hypervariable domain, and an acidic C-terminal domain. Maturation of HAstV requires proteolytic processing of the astrovirus CP both inside and outside the host cell, resulting in the removal of the C-terminal domain and the breakdown of the rest of the CP into three predominant protein species with molecular masses of ∼34, 27/29, and 25/26 kDa, respectively. We have now solved the crystal structure of VP9071–415 (amino acids [aa] 71 to 415 of VP90) of human astrovirus serotype 8 at a 2.15-Å resolution. VP9071–415 encompasses the conserved N-terminal domain of VP90 but lacks the hypervariable domain, which forms the capsid surface spikes. The structure of VP9071–415 is comprised of two domains: an S domain, which adopts the typical jelly-roll β-barrel fold, and a P1 domain, which forms a squashed β-barrel consisting of six antiparallel β-strands similar to what was observed in the hepatitis E virus (HEV) capsid structure. Fitting of the VP9071–415 structure into the cryo-electron microscopy (EM) maps of HAstV produced an atomic model for a continuous, T=3 icosahedral capsid shell. Our pseudoatomic model of the human HAstV capsid shell provides valuable insights into intermolecular interactions required for capsid assembly and trypsin-mediated proteolytic maturation needed for virus infectivity. Such information has potential applications in the development of a virus-like particle (VLP) vaccine as well as small-molecule drugs targeting astrovirus assembly/maturation.IMPORTANCE Human astrovirus (HAstV) is a leading cause of viral diarrhea in infants and young children worldwide. As a nonenveloped virus, HAstV exhibits an intriguing feature in that its maturation requires extensive proteolytic processing of the astrovirus capsid protein (CP) both inside and outside the host cell. Mature HAstV contains three predominant protein species, but the mechanism for acquired infectivity upon maturation is unclear. We have solved the crystal structure of VP9071–415 of human astrovirus serotype 8. VP9071–415 encompasses the conserved N-terminal domain of the viral CP. Fitting of the VP9071–415 structure into the cryo-EM maps of HAstV produced an atomic model for the T=3 icosahedral capsid. Our model of the HAstV capsid provides valuable insights into intermolecular interactions required for capsid assembly and trypsin-mediated proteolytic maturation. Such information has potential applications in the development of a VLP vaccine as well as small-molecule drugs targeting astrovirus assembly/maturation.

Isolation of Neutralizing Monoclonal Antibodies to Human Astrovirus and Characterization of Virus Variants That Escape Neutralization

“…To identify the neutralization epitopes on the HAstV capsid, we first evaluated the capacity of the core and spike domains to induce total (determined by enzyme-linked immunosorbent assay [ELISA]) and neutralizing antibodies. These two structural domains of the virus can be produced in Escherichia coli in a soluble and correctly folded form (10)(11)(12)(13)(14). Rabbits and mice were immunized with either the purified, recombinant core or the spike domain of HAstV-1 (core1 or spike1).…”

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Transition metal complexes of nano bidentate organometallic Schiff base: Preparation, structure characterization, biological activity, DFT and molecular docking studies

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