Research Progress Towards Poliovirus Virus-like Particle Vaccines: A Review

Figures

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  Figure 1. Schematic diagram of poliovirus’s genomic structure and VLP assembly [8,16,17]. This figure was created by the authors based on [8,16,17]. The PV genome is a single positive-sense RNA molecule which includes a 5′ UTR containing an internal ribosomal entry site (IRES), a 3′ UTR, and a poly(A) tail. The open reading frame (ORF) encodes a polyprotein processed into structural (P1) and nonstructural (P2, P3) regions. P1 is cleaved into VP0, VP3, and VP1 by the 3CD protease. A 5S protomer is assembled from one copy of VP0, VP3, and VP1, and five protomers are assembled into a 14S pentamer. In the absence of viral genomic RNA, 80S empty particles (C-antigen) are self-assembled from these pentamers. After viral genome encapsidation, a 150S particle is formed; VP0 is further cleaved into VP4 and VP2, and mature 160S virions (D-antigen) are consequently formed. Heating or improper handling of viral particles can induce the conversion from D-antigens to C-antigens.

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  Figure 2. PV2 wtVLP and sVLP co-expression strategy [33]. This figure is reproduced from [33]. TRP2-L and TRP2-R, the up- and downstream parts of the TRP region; PAOX1, AOX1 promoter; CYC1 TT, CYC1 transcription termination region; ADE2, expression cassette encoding phosphoribosylaminoimidazole carboxylase, used as the selection marker.

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  Figure 3. Cryo-EM structures of D-antigen and C-antigen particles of poliovirus Type 1 (Mahoney strain) [9]. This figure is reproduced from [9]. D-antigen: Radially colored isosurface of refined particles at high contour (160S (left panel)); C-antigen: Radially colored isosurface of early 135S particles at high contour (σ = 5), showing an opening at the 2-fold axis (right panel). Scale bar indicates the radial range corresponding to each color.