African swine fever virus (ASFV), the causative pathogen of the recent ASF epidemic, is a highly contagious double-stranded DNA virus. Its genome is in the range of 170~193 kbp and encodes 68 structural proteins and over 100 non-structural proteins. Its high pathogenicity strains cause nearly 100% mortality in swine. Consisting of four layers of protein shells and an inner genome, its structure is obviously more complicated than many other viruses, and its multi-layered structures play different kinds of roles in ASFV replication and survival. Each layer possesses many proteins, but very few of the proteins have been investigated at a structural level. Here, we concluded all the ASFV proteins whose structures were unveiled, and explained their functions from the view of structures. Those structures include ASFV AP endonuclease, dUTPases (E165R), pS273R protease, core shell proteins p15 and p35, non-structural proteins pA151R, pNP868R (RNA guanylyltransferase), major capsid protein p72 (gene B646L), Bcl-2-like protein A179L, histone-like protein pA104R, sulfhydryl oxidase pB119L, polymerase X and ligase. These novel structural features, diverse functions, and complex molecular mechanisms promote ASFV to escape the host immune system easily and make this large virus difficult to control.

Porcine reproductive and respiratory syndrome virus (PRRSV) is prevalent throughout the world and has caused great economic losses to the swine industry. Nonstructural protein 10 (nsp10) is a superfamily 1 helicase participating in multiple processes of virus replication and one of the three most conserved proteins in nidoviruses. Here we report three high resolution crystal structures of highly pathogenic PRRSV nsp10. PRRSV nsp10 has multiple domains, including an N-terminal zinc-binding domain (ZBD), a β-barrel domain, a helicase core with two RecA-like domains, and a C-terminal domain (CTD). The CTD adopts a novel fold and is required for the overall structure and enzymatic activities. Although each domain except the CTD aligns well with its homologs, PRRSV nsp10 adopts an unexpected extended overall structure in crystals and solution. Moreover, structural and functional analyses of PRRSV nsp10 versus its closest homolog, equine arteritis virus nsp10, suggest that DNA binding might induce a profound conformational change of PRRSV nsp10 to exert functions, thus shedding light on the mechanisms of activity regulation of this helicase.In 2006, a large-scale atypical PRRS outbreak caused by the highly pathogenic PRRSV (HP-PRRSV, belonging to PRRSV-2) emerged in China [13,14]. Yan Li and her colleagues demonstrated that nsp9 and nsp10 together contributed to the replication efficiency and the high virulence of HP-PRRSV [15]. Nsp9 contains an RNA-dependent RNA-polymerase (RdRp) domain [16]. Nsp10 belongs to the superfamily 1B (SF1B) Upf1-like family of helicases, which could unwind both DNA and RNA duplexes [17][18][19]. In addition, this family of helicases contains an N-terminal predicted zinc-binding domain (ZBD) which is conserved in all nidovirus helicases, including 12 or 13 conserved Cys and His residues [20]. However, the C-terminal domain (CTD) is variable among nidoviruses. Besides, nsp10 can vary up to approximately 42% on the amino acid level between the two genotypes, and the strains within PRRSV-2 also vary considerably with amino acid differences as high as 8% [21,22]. We previously reported the first structure of the nidovirus helicase, equine arteritis virus (EAV; family Arteriviridae) nsp10, and demonstrated that the CTD perhaps exerts a regulatory function on the helicase core, facilitating coupling between NTPase and polynucleotide binding activities [23]. Another solved structure of nidovirus helicase is Middle East respiratory syndrome coronavirus (MERS-CoV; family Coronaviridae) nsp13 [24]. While the domain organization of nsp13 is similar to EAV nsp10, structural comparisons of the individual domains showed that nsp13 is closely related to Upf1. The N-terminal Cys-His-rich domain (CH domain) of nsp13 is more related to the CH of Upf1 than to the ZBD of EAV nsp10. The helicase core of EAV nsp10 is more compact than that of MERS-CoV nsp13 which has a similar size as Upf1. Meanwhile, MERS-CoV nsp13 does not contain a C-terminal regulatory domain homologous to the CTD of EAV nsp10.Reflecting its ...

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