Proteolytic processing of the astrovirus capsid

J Virol. 2000 Feb;74(4):1810-4. doi: 10.1128/jvi.74.4.1810-1814.2000.

Abstract

To further characterize the nature of proteolytic processing of the astrovirus capsid, we infected Caco-2 cells with a high multiplicity of astrovirus without trypsin in the presence of 5 to 10% fetal calf serum. These infections were characterized by pulse-chase labeling with [35S]Smethionine, electron microscopy, gel electrophoresis of purified viral particles, and analysis of infectivity of such particles with and without added trypsin. Pulse-chase experiments showed that the astrovirus capsid protein was initially translated as an approximately 87-kDa protein. The 87-kDa capsid protein was rapidly converted intracellularly to a 79-kDa form which was found in smaller amounts in the cell supernatant. Purification by differential centrifugation yielded particles that appeared quite similar to trypsin-grown astrovirus particles by negatively stained electron microscopy. These particles were antigenically distinct from trypsin-treated virions as demonstrated by their various reactions with monoclonal antibodies in a solid-phase immunoassay. The purified trypsin-free particles were mainly composed of the 79-kDa capsid protein which was found to have an amino terminus at residue 71 of the entire open reading frame 2 (ORF2) product. The cleavage site was identified in a highly conserved region of the astrovirus ORF2 product. These trypsin-free particles were minimally infectious in cultured Caco-2 cells but became highly infectious (10(5)-fold increase) after trypsin but not chymotrypsin treatment. This trypsin-enhanced infectivity correlated with conversion of the 79-kDa capsid protein to three smaller peptides of approximately 34, 29, and 26 kDa.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antigens, Viral
  • Caco-2 Cells
  • Capsid / metabolism*
  • Humans
  • Mamastrovirus / metabolism*
  • Mamastrovirus / physiology
  • Mamastrovirus / ultrastructure
  • Protein Precursors / metabolism
  • Protein Processing, Post-Translational*
  • Trypsin
  • Virion / ultrastructure

Substances

  • Antigens, Viral
  • Protein Precursors
  • Trypsin