Browsing by Author "Harper, Justin"

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    Crystal Structure of the Human Astrovirus Capsid Protein
    (American Association for Microbiology, 2016) Toh, Yukimatsu; Harper, Justin; Dryden, Kelly A.; Yeager, Mark; Arias, Carlos F.; Méndez, Ernesto; Tao, Yizhi Jane
    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.
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    Human astrovirus capsid protein releases a membrane lytic peptide upon trypsin maturation
    (American Society for Microbiology, 2023) Ykema, Matthew; Ye, Kai; Xun, Meng; Harper, Justin; Betancourt-Solis, Miguel A.; Arias, Carlos F.; McNew, James A.; Tao, Yizhi Jane
    The human astrovirus (HAstV) is a non-enveloped, single-stranded RNA virus that is a common cause of gastroenteritis. Most non-enveloped viruses use membrane disruption to deliver the viral genome into a host cell after virus uptake. The virus–host factors that allow for HAstV cell entry are currently unknown but thought to be associated with the host-protease-mediated viral maturation. Using in vitro liposome disruption analysis, we identified a trypsin-dependent lipid disruption activity in the capsid protein of HAstV serotype 8. This function was further localized to the P1 domain of the viral capsid core, which was both necessary and sufficient for membrane disruption. Site-directed mutagenesis identified a cluster of four trypsin cleavage sites necessary to retain the lipid disruption activity, which is likely attributed to a short stretch of sequence ending at arginine 313 based on mass spectrometry of liposome-associated peptides. The membrane disruption activity was conserved across several other HAstVs, including the emerging VA2 strain, and effective against a wide range of lipid identities. This work provides key functional insight into the protease maturation process essential to HAstV infectivity and presents a method to investigate membrane penetration by non-enveloped viruses in vitro.
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    The Induction of Infectivity in Human Astrovirus in Response to Capsid Proteolysis
    (2013-06-28) Harper, Justin; Tao, Yizhi Jane; McNew, James A.; Stewart, Charles R.
    Astrovirus is a non-enveloped, T=3, positive-sense RNA virus that presents with self-limiting gastroenteritis; however, it has been additionally associated with serious presentations such as nephritis, hepatitis, and encephalitis, which is compounded by its propensity to engage in cross-species penetrations. Astrovirus undergoes a complex capsid maturation process mediated by host proteases in which an inert, immature capsid composed of VP90 is sequentially cleaved to yield a highly infectious particle composed of VP34 and VP27/VP25, which form the capsid shell and spikes, respectively. By overexpressing a VP9070-418 truncate in insect cells, we have demonstrated that the shell domain alone cannot support particle assembly, implying a crucial role for the dimeric contacts within the spike. Various monomeric, shell domain truncates (i.e. VP9071-252, VP9071-283, VP9071-313, and VP9071-415) have been successfully expressed and purified, but none yielded useful crystals, suggesting the structural context of the capsid lattice may be needed to stabilize their conformational flexibility.