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Review
. 2017 Jun;24:105-114.
doi: 10.1016/j.coviro.2017.05.004. Epub 2017 Jun 8.

Structure and Organization of Paramyxovirus Particles

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Free PMC article
Review

Structure and Organization of Paramyxovirus Particles

Robert M Cox et al. Curr Opin Virol. .
Free PMC article

Abstract

The paramyxovirus family comprises major human and animal pathogens such as measles virus (MeV), mumps virus (MuV), the parainfluenzaviruses, Newcastle disease virus (NDV), and the highly pathogenic zoonotic hendra (HeV) and nipah (NiV) viruses. Paramyxovirus particles are pleomorphic, with a lipid envelope, nonsegmented RNA genomes of negative polarity, and densely packed glycoproteins on the virion surface. A number of crystal structures of different paramyxovirus proteins and protein fragments were solved, but the available information concerning overall virion organization remains limited. However, recent studies have reported cryo-electron tomography-based reconstructions of Sendai virus (SeV), MeV, NDV, and human parainfluenza virus type 3 (HPIV3) particles and a surface assessment of NiV-derived virus-like particles (VLPs), which have yielded innovative hypotheses concerning paramyxovirus particle assembly, budding, and organization. Following a summary of the current insight into paramyxovirus virion morphology, this review will focus on discussing the implications of these particle reconstructions on the present models of paramyxovirus assembly and infection.

Figures

Figure 1
Figure 1
A) Model of an MeV virion in which the matrix protein coats the nucleocapsid protein. The viral envelope is shown in orange. The nucleocapsid proteins are shown in cyan. The fusion protein trimers are shown in red. The attachment glycoprotein tetramers are shown as green. Matrix protein depicted is from Newcastle disease virus (PDB 4g1g). Viral glycoproteins are based on PIV5 (PDB: 4gip for the F protein; PDB ID: 4jf7 and 3tsi for the PIV5 HN ectodomain and stalk, respectively. The vesicular stomatitis virus L protein structure (yellow) was used to represent the unknown paramyxovirus L conformation (PDB ID: 5a22). The phosphoprotein (brown) was modeled using the oligomerization domain of measles P (PDB ID: 3zdo). B) A model of an MeV virion in which a matrix protein array is located at the inner leaflet of the viral membrane. The matrix protein is shown in blue. The matrix-coated nucleocapsids were created using Chimera [92] using electron density maps EMD-1973 and EMD-1974 [43]. PDB structures were created in PyMOL [93].
Figure 2
Figure 2
Organization of the paramyxovirus nucleocapsid. A) Nucleocapsid proteins for all paramyxoviruses form helical assemblies of N proteins encapsidating the viral RNA (shown in this model are MeV RNPs, N proteins are depicted in cyan and forest green, the RNA is colored in red) (PDB ID: 4UFT). BD) While RNPs for 20 nm diameter tubules, MeV RNPs were also found M protein wrapped in larger diameter 30 nm tubules [43]. Matrix proteins are shown in dark blue and nucleocapsids in cyan. Top view (B) and side view (C) of the 30 nm tubules depicting the distinct cylindrical M complex surrounding the MeV nucleocapsid. D) A clipped model of the 30 nm tubule structure. The matrix coated nucleocapsids were created using Chimera [92] based on electron density maps EMD-1973 and EMD-1974 [43].
Figure 3
Figure 3
Models of alternative spatial organizations of the paramyxovirus glycoproteins on the virion surface. A) The overall organization of the paramyxovirus glycoproteins was thought to be random with an undetermined relative stoichiometry of individual fusion protein trimers (red) and attachment protein tetramers (green). B, C, D) In a recent study [25], an arrangement of NiV F protein trimers into hexamers of trimers and higher order complexes was proposed. Schematics of hexameric F trimer arrangements in contact with one (A) or multiple (B) attachment protein tetramers and higher order F assemblies consisting of interacting hexamers of trimers (C). Different hypothetical contacts of the F assemblies with attachment protein tetramers are shown, but the stoichiometry and positioning of the attachment protein oligomers relative to the F protein complexes has not yet been defined.

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