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Architecture of African swine fever virus and implications for viral assembly

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Science  01 Nov 2019:
Vol. 366, Issue 6465, pp. 640-644
DOI: 10.1126/science.aaz1439
  • Fig. 1 Architecture of the ASFV virion.

    (A) The central slice (left) and cross section (right) of the icosahedral ASFV virion structure. The outer membrane, capsid, inner membrane, core shell, and nucleoid are colored in orange, magenta, deep blue, cyan, and gray, respectively. The radius and thickness of each layer are labeled. (B) Radially colored representations of the ASFV capsid and core shell. The T number, including the h and k vectors, is indicated. The color scale represents radial distance in angstroms. (C) Cryo-EM reconstruction of the ASFV capsid. The left half shows the trisymmetron and pentasymmetry organization, and the trisymmetrons, pentasymmetrons, and zippers (the boundaries of two neighboring trisymmetrons) are colored in yellow, light purple, and cyan, respectively. The right half shows the density of the minor capsid proteins, including the penton proteins after removing the outer capsid shell; each minor capsid protein is shown in a different color, as indicated at the bottom right. Boxes in green, red, and blue show the locations with the representative capsomer assembly patterns that will be discussed in Fig. 2D. (D) Diagrammatic organization of the minor capsid proteins and capsomers as viewed from inside the capsid. The pseudo-hexameric capsomers are outlined. The icosahedral threefold and twofold axes are shown as solid black triangles and ovals, respectively. Different minor capsid proteins, including the penton proteins, are shown as different shapes with different colors, as indicated at the bottom right. The pseudo-hexameric capsomers are labeled A, B, C, … in the trisymmetrons and a, b, c, … in the pentasymmetrons.

  • Fig. 2 Structure and organization of p72.

    (A) Density maps and atomic model of the p72 trimer. Each subunit is depicted in a different color. Side-chain features are illustrated on the right. Residues with side chains are labeled. Single-letter abbreviations for the amino acid residues are as follows: E, Glu; F, Phe; G, Gly; I, Ile; K, Lys; L, Leu; N, Asn; Q, Gln; R, Arg; S, Ser; V, Val; W, Trp; and Y, Tyr. (B) Ribbon diagram of the p72 monomer. The domains base, JR1 (jelly roll 1), JR2 (jelly roll 2), and ER1 to ER4 are presented in different colors. (C) Surface presentation of the p72 trimer. ER1 to ER4 domains are depicted in the same colors as in (B); other parts are colored in gray. (D) Detailed depictions of three distinct assembly patterns according to their locations: in the trisymmetron (left), zipper (middle), and pentasymmetron (right). The identities of p72 capsomers are labeled according to the location, as in Fig. 1D. Three types of interaction mode—head to back, head to head, and back to back—are indicated by green, red, and blue triangles, respectively. Interaction areas between two capsomers are measured and marked. Notably, the capsomer interactions in the same interaction mode vary under different microenvironments. These are labeled as 1, 1′; 2, 2′; or 3, 3′, 3′′. The cartoon models depict the changed microenvironments. The diagrams in the dashed boxes show the detailed structural organization in the different microenvironments.

  • Fig. 3 Extensive intermolecular networks from minor capsid proteins underpin capsid stability.

    (A) Cryo-EM map of the penton complex (top). Each subunit of the penton is depicted in a different color, and the pentameric p49 is colored in magenta. The putative homologous structure of the mavirus penton protein is fitted into the ASFV penton cryo-EM map (bottom). (B) Structures of the p17 minor capsid proteins that glue together capsomers within each trisymmetron. Three copies of p17 molecules from one p72 capsomer are depicted in three colors (red, green, and blue), and p72 capsomers are shown as cartoons. (C) Overview of the intermolecular contacts at the inner capsid. One zipper and two neighboring pentasymmetrons are shown with the p72 capsomers labeled. The view is from the inside of the capsid, and the color scheme is the same as that in Fig. 1D. The diagrams labeled (i) to (iv) show enlarged views of the interactions indicated by the dashed boxes.

  • Fig. 4 The proposed assembly pathway for the ASFV capsid.

    (A) Formation of the penton cores on the inner membrane. The ASFV capsid assembly begins with appearance of viral inner membrane precursors that envelop the core shell and nucleoid progressively. During the early stage, the inner membranes exhibit generally open structures, with various inner membrane proteins, for example, p17, floating on them. The penton complexes associate with the inner membrane and then recruit p72 capsomers to form the penton cores, initiating the assembly. (B) Correct assembly of the zipper structures mediated by skeleton protein M1249L and p17 and p72 capsomers. (C) Construction of the polyhedral cage by 12 pentasymmetrons and 30 zippers. (D) Accompanying the formation of the polyhedral framework, p72 capsomers fill in the trisymmetrons to complete the capsid assembly.

Supplementary Materials

  • Architecture of African swine fever virus and implications for viral assembly

    Nan Wang, Dongming Zhao, Jialing Wang, Yangling Zhang Ming Wang, Yan Gao, Fang Li, Jingfei Wang, Zhigao Bu, Zihe Rao, Xiangxi Wang

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 to S10
    • Tables S1 to S3
    • References

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