Abstract
Parechoviruses belong to the genus Parechovirus within the family Picornaviridae and are non-enveloped icosahedral viruses with a single-stranded RNA genome. Parechoviruses include human and animal pathogens classified into six species. Those that infect humans belong to the Parechovirus A species and can cause infections ranging from mild gastrointestinal or respiratory illness to severe neonatal sepsis. There are no approved antivirals available to treat parechovirus (nor any other picornavirus) infections. In this parechovirus review, we focus on the cleaved protein products resulting from the polyprotein processing after translation comparing and contrasting their known or predicted structures and functions to those of other picornaviruses. The review also includes our original analysis from sequence and structure prediction. This review highlights significant structural differences between parechoviral and other picornaviral proteins, suggesting that parechovirus drug development should specifically be directed to parechoviral targets.
Highlights
Parechoviruses belong to a single genus within a large family, Picornaviridae, which comprise small, icosahedral, non-enveloped, single-stranded RNA viruses approximately 30 nm in diameter
The Parechovirus genus is currently divided into six species Parechovirus A-F (PeV-A-F) out of which PeV-A contains human parechoviruses
We summarize current knowledge on the structure of the parechovirus virion as well as the royalsocietypublishing.org/journal/rsob Open Biol. 11: 210008
Summary
Parechoviruses belong to a single genus within a large family, Picornaviridae, which comprise small, icosahedral, non-enveloped, single-stranded RNA (ssRNA) viruses approximately 30 nm in diameter. CryoEM and X-ray data on the mature human parechoviruses PeV-A1 and PeV-A3, as well as PeV-B1 enabled detailed characterization of the viral capsid; there are no structural data available for parechoviral non-structural proteins [14,20,21,22,23]. We aligned amino acid sequences of non-structural proteins from six parechovirus isolates, each from different species, and from an unassigned Rattus tanezumi parechovirus (RtPV) (table 1). These sequences were compared to the sequences of the homologous proteins for which molecular models are available in the Protein Data Bank (PDB). Parechoviruses exhibit at least six distinct features at both structural and functional level which are different from that of many other picornaviruses, which we will discuss in detail later, but summarize here. (i) VP0 is not cleaved nor myristoylated in parechoviruses [29,30]. (ii) A lipid factor, present in the hydrophobic pocket in VP1 of many enteroviruses, is absent from the parechovirus capsids [20,21,22,23]. (iii) The interactions between multiple packaging signals in genomic ssRNA and capsid proteins occurs at different sites in parechoviruses compared to enteroviruses [31,32]. (iv) The parechovirus 2A protein is homologous to eukaryotic phospholipid-metabolizing enzymes [33]. (v) Parechoviruses do not cause protein synthesis shut-off during virus replication described for enteroviruses [34]. (vi) As opposed to the guanidine hydrochloride sensitive 2C protein from enteroviruses, parechovirus infection is resistant to guanidine hydrochloride, revealing a functional difference between parechovirus and enterovirus 2C proteins [35]
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