Structure and Composition of picornaviruses
المؤلف:
Stefan Riedel, Jeffery A. Hobden, Steve Miller, Stephen A. Morse, Timothy A. Mietzner, Barbara Detrick, Thomas G. Mitchell, Judy A. Sakanari, Peter Hotez, Rojelio Mejia
المصدر:
Jawetz, Melnick, & Adelberg’s Medical Microbiology
الجزء والصفحة:
28e , p531
2025-12-03
13
The virion of enteroviruses and rhinoviruses consists of a capsid shell of 60 subunits, each of four proteins (VP1–VP4) arranged with icosahedral symmetry around a genome made up of a single strand of positive-sense RNA (Figure 1). Parechoviruses are similar except that their capsids contain only three proteins because VP0 does not get cleaved into VP2 and VP4.
Fig1. Structure of a typical picornavirus. A: Exploded diagram showing internal location of the RNA genome surrounded by capsid composed of pentamers of proteins VP1, VP2, VP3, and VP4. Note the “canyon” depression surrounding the vertex of the pentamer. B: Binding of cellular receptor to the floor of the canyon. The major rhinovirus receptor (intercellular adhesion molecule-1 [ICAM-1]) has a diameter roughly half that of an immunoglobulin G (IgG) antibody molecule. C: Location of a drug-binding site in VP1 of a rhinovirus. The antiviral drug shown, WIN 52084, prevents viral attachment by deforming part of the canyon floor. (Reproduced with permission from Rueckert RR: Picornaviridae: The viruses and their replication. In Fields BN, Knipe DM, Howley PM [editors-in-chief]. Fields Virology, 3rd ed. Lippincott-Raven, 1996.)
By means of x-ray diffraction studies, the molecular structures of poliovirus and rhinovirus have been determined.
The three largest viral proteins—VP1, VP2, and VP3—have a very similar core structure in which the peptide backbone of the protein loops back on itself to form a barrel of eight strands held together by hydrogen bonds (the β barrel). The amino acid chain between the β barrel and the amino and carboxyl terminal portions of the protein contains a series of loops. These loops include the main antigenic sites that are found on the surface of the virion and are involved in the neutralization of viral infection.
There is a prominent cleft or canyon around each pentameric vertex on the surface of the virus particle. The receptor-binding site used to attach the virion to a host cell is thought to be located near the floor of the canyon. This location would presumably protect the crucial cell attachment site from structural variation influenced by antibody selection in hosts because the canyon is too narrow to permit deep penetration of antibody molecules (Figure 1).
The genome RNA ranges in size from 7.2 kb (human rhinovirus) to 7.4 kb (poliovirus, hepatitis A virus) to 8.4 kb (aphthovirus). The organization of the genome is similar for all (Figure 2). The genome is polyadenylated at the 3′ end and has a small viral-coded protein (VPg) covalently bound to the 5′ end. The positive-sense genomic RNA is infectious.
Fig2. Organization and expression of the picornavirus genome. The viral genomic RNA has genome-linked VPg protein at the 5′ end and is polyadenylated at the 3′ terminus. L specifies a leader protein found in cardioviruses and aphthoviruses but not in enteroviruses, human rhinoviruses, or human hepatitis virus A. The plus-sense single-stranded RNA genome is translated into a single polyprotein. The P1 domain (red) encodes capsid proteins, and the P2 (green) and P3 (blue) domains encode noncapsid proteins used for protein processing and replication. Cleavage of the polyprotein is accomplished by virus-coded proteinases 2A and 3C. Protein 2A performs early cleavages of the polyprotein, and all other cleavages are performed by proteinase 3C. (Reproduced with permission from Kerkvliet J, Edukulla R, Rodriguez M: Novel roles of the picornaviral 3D polymerase in viral pathogenesis. Adv Virol 2010;368068. Copyright © 2010 Jason Kerkvliet et al.)
Whereas enteroviruses are stable at acid pH (3.0–5.0) for 1–3 hours, rhinoviruses are acid labile. Enteroviruses and some rhinoviruses are stabilized by magnesium chloride against thermal inactivation. Enteroviruses have a buoyant density in cesium chloride of about 1.34 g/mL; human rhino viruses, about 1.4 g/mL.
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