Structural and functional characterization of the severe fever with thrombocytopenia syndrome virus L protein

Severe fever with thrombocytopenia syndrome virus (SFTSV) belongs to the Bunyavirales order. For preventing the bad consequence of this disease, specific vaccine and antiviral drugs are necessary. Viral mRNAs are transcribed by RNA-dependent RNA polymerase L protein that is responsible for the replication of viral genome. So, this is a target point of drug development. This scientific paper revealed the expression and purification procedure of full-length L protein of SFTSV using electron cryo-microscopy and X -ray crystallography. Researcher prevailed 3D models with 70% L protein, polymerase core region, the endonuclease and cap-binding domains. The comprehensive study of structural & biochemical characterization was performed between SFTSV L protein with La Crosse peribunyavirus and influenza orthomyxovirus polymerases to deliver a well-founded structure for futures research of L protein, RNA synthesis and expansion of antiviral strategies against this group.

(AR)

The proprotein convertase SKI-1/S1P is a critical host factor for Nairobi sheep disease virus infectivity

Nairobi sheep disease virus (NSDV) is a tick-borne viral disease of sheep and goats belongs to Orthonairovirus from Bunyavirales order and characterized by fever, haemorrhagic gastroenteritis, abortion, and high mortality. This virus is genetically related to human-pathogenic Crimean-Congo haemorrhagic fever virus (CCHFV) made it proposed as a model organism for researching CCHFV pathogenesis. However, little is known about NSDV pathogenesis and virus-host interactions. The life cycle of human-pathogenic CCHFV is depends on SKI-1/S1P, an important enzyme in the cell’s cholesterol control mechanism. Previous studies have demonstrated that the CCHFV GPC is cleaved by SKI-1/S1P at the consensus motif RRLL519 (amino acid position refers to CCHFV-IbAr 10,200), and this proteolytic cleavage has a strong impact on virus infectivity. Therefore, the aim of this study was to observe the role of SKI-1/S1P expression in NSDV replication and infectivity. The result presented in this study highlights the critical role played by the host cell protease SKI-1/S1P in NSDV replication and infectivity. The findings imply that SKI-1/S1P may be an essential orthonairovirus host factor, which is consistent with the early observation on the function of SKI-1/S1P in the CCHFV life cycle. This study also offers the first proof of the inhibitory small molecule, PF-429242’s antiviral action against NSDV. These results could be the base for further research to assess PF-429242 effectiveness against different orthonairovirus, such as the human pathogenic CCHFV.

(MA)

Comparative Structural and Functional Analysis of Bunyavirus and Arenavirus Cap-Snatching Endonucleases

The cap-snatching mechanism exists in Segmented negative strand RNA viruses (sNSVs) of the arena-, bunya- and orthomyxovirus for mRNA synthesis. Authors focused on that the location of cap-binding domain was not confirmed in bunya- and arenavirus. To confirm the locations and profile of cap-snatching nuclease, they analyzed three dimensional structures, shift of melting temperature of endonuclease crystal in with/without divalent metal ions, Hantaan (one of Bunyavirus) endonuclease activity rates in comparison with other sNSVs, mutational analysis of endonuclease activity, iron induced stability of Hantaan endonuclease, structural characterization of divalent metal ions binding to Lassa (one of Arenavirales) endonuclease and mutational analysis of endonuclease activity, iron induced stability of Lassa endonuclease. These results showed that there are 2 types of endonucleases in sNSVs. One is for orthomyxovirus and bunyavirus and contains characteristic catalytic histidine. The other is for arenavirus without histidine and shows poorer activity.

(NN)

Optimal Expression of the envelope Glycoprotein of Orthobrornaviruses Determines the Production of Mature Virus Particles

Borna disease virus 1, a member of the genus Orthobornavirus, is characterized by its long term gene expression. For improving reproduction RNA virus-based episomal vector system, authors focused on that expression of G protein which is type I surface glycoprotein and contains signal peptide is important for Bornavirus infection to cell. They confirmed the importance of G expression for reproduction of infectious viral particles. As the results, excessive G expression of most Bornavirus except canary bornavirus didn’t affect reproduction but reduces infectious reproduced particles with mature G and genomic RNA. These results suggest that limitation of G expression is necessary for normal Borna viral particle production, because increased pre-G inhibits cleavage of G and introduction of mature-G and viral genomic RNA into particles.

(NN)

Single-cell profiling of lncRNA expression during Ebola virus infection in rhesus macaquas

Not bulk tissue analysis but single-cell RNA sequences are necessary for uncovering current gene expression value and tissue specificity. Especially, Ebola virus (EBOV) causes one of most lethal infectious disease and strong inflammatory to humans. Single-cell analysis of circulating monocytes could uncover that correct gene expression value, regulation, and tissue or cell specificity. As the results, they identified 2 times lncRNA by annotating them with single-cell RNA sequences. Expression of lncRNA was in fewer cells than mRNA. Some lncRNA were regulated on EBOV infection. These results show that single-cell RNA sequence is effective for measuring correct lncRNA expression. Some of lncRNA expression can be in only specific cells. LncRNA whose expression is condition or cell-type specific are candidates of disease biomarkers.

(NN)

“Rule of Six”: How Does the Sendai Virus RNA Polymerase Keep Count?

The “Rule of six” stipulates that the Paramyxovirus polymerase efficiently replicate 6n+0 nucleotides genomes especially. Sendai virus (SeV), a member of paramyxovirus, was used through this series of experiments in this study. As the results, SeV RNA polymerase showed selectivity for RNA following to rule of six without C protein. Swap editing site of SeV RNA was effective for length correction. Experiment of constructs with extra 3’-OH sequences showed that the 3’-OH congruence was not an important signal for SeV RNA polymerase. Furthermore, 2 promoters, working independently, were confirmed. Initiation for one promoter was antigenomic promoter, for another was genomic promoter and both obeyed to rule of six. These results showed that the observance of the rule of six can be necessary for polymerase recognition of certain nucleotides properly positioned regarding the nucleoprotein interaction points for appropriate replication.

(NN)

Mechanistic basis for potent neutralization of Sin Nombre hantavirus by a human monoclonal antibody

Sin Nombre virus (SNV) belonging to Hantaviridae family, is responsible for causing hantavirus cardiopulmonary syndrome, a severe illness associated with high fatality. The transmission of SNV to humans can occur via inhalation of aerosolized excreta from rodent. Gn an Gc, the spike proteins on hantavirus, play an essential role as recognized compartment for antibodies. Prior research suggested that Gn-targeting mAbs potentially enhance neutralization ability against hantavirus. As an effective neutralizing human monoclonal antibody, SNV-42 was isolated from a memory B cell originating from a convalescent SNV donor.  This study aims to evaluate the neutralizing mechanism of SNV-42 through from genetic analysis and protein structure analysis. SNV-42 maintains gene segment which serves a vital part in promoting affinity maturation of antibodies, thereby enhancing antibody specificity. The results of crystallographic analysis on SNV-42 protein binding to SNV Gn protein suggests SNV-42 is capable of interfering with various stages of the viral entry pathway. Subsequently, overlaying SNV-42 and SNV (Gn−Gc) ultrastructure arrangement indicates SNV-42 combine to the distal region of SNV membrane. Furthermore, the researchers conduct a simulation to investigate the interaction between SNV-42 protein and SNV Gn spike protein, suggesting SNV-42 might contribute to receptor blocking and fusion inhibition.

(HW)