Editing Parvoviridae (section)

==Structure==
[[File:Parvoviridae virion.jpg|thumb|250 px|Schematic diagram of a ''Parvoviridae'' [[virion]]]]
[[File: 4dpv.jpg|thumb|250 px|A diagram of the canine parvovirus's capsid, containing 60 monomers of the capsid protein.]]
Parvovirus virions are 23–28 nanometers (nm) in diameter and consist of the genome enclosed inside a capsid that is [[Icosahedron|icosahedral]] in shape with a rugged surface. The capsid is composed of 60 structurally equivalent polypeptide chains derived from the C-terminal end of a VP protein's sequence, interlocking extensively to form an icosahedron with 60 asymmetric, superficial triangular units. These units have 3-fold [[radial symmetry]] at two vertices and 5-fold radial symmetry at one, with 2-fold radial symmetry at the line opposite of the 5-fold vertex and a 2/5 circular fold wall surrounding the point of the 5-fold vertex. Twenty 3-fold vertices, thirty 2-fold lines, and twelve 5-fold vertices exist per capsid, the latter corresponding to the 12 vertices of the icosahedron.<ref name=cotmoreictv />

Typical features of the capsid surface include depressions at each 2-fold axis, elevated protrusions surrounding the 3-fold axes, and raised cylindrical projections made of five beta-barrels<ref name=qiu >{{cite journal |vauthors=Qiu J, Söderlund-Venermo M, Young NS |date=January 2017 |title=Human Parvoviruses |journal=Clin Microbiol Rev |volume=30 |issue=1 |pages=43–113 |doi=10.1128/CMR.00040-16 |pmc=5217800 |pmid=27806994}}</ref> surrounded by canyon-like depressions at the 5-fold axes. Each of these cylinders potentially contains an opening to connect the exterior of the capsid to the interior, which mediates entry and exit of the genome. About 20 nucleotides from the 5′-end of the genome may remain exposed outside of the capsid carrying a copy of NS1 bound to the 5′-end, which is a result of how the genome is synthesized and packaged.<ref name=cotmoreictv />

Varying sizes of the VP protein are expressed for different parvoviruses, the smaller ones, VP2–5, being expressed at a higher frequency than the large size, VP1. The smaller VPs share a common C-terminus with different N-terminus lengths due to truncation. For VP1, the N-terminus is extended to contain regions important in the replication cycle, and it is incorporated into the capsid, typically 5–10 per capsid, with the common C-terminus responsible for assembling capsids.<ref name=mietzsch /><ref name=cotmoreictv />

Each VP monomer contains a core beta-barrel structure called the [[Jelly roll fold|jelly roll motif]] of eight strands arranged in two adjacent antiparallel beta sheets, labeled CHEF and BIDG after the individual strands, the latter forming the interior surface of the capsid. Individual beta strands are connected by loops that have varying length, sequence, and conformation, and most of these loops extend toward the exterior surface, giving parvoviruses their unique, rough surface. Related parvoviruses share their surface topologies and VP protein folds to a greater degree than their sequence identities, so the structure of the capsid and capsid protein are useful indicators of phylogeny.<ref name=mietzsch /><ref name=cotmoreictv />