Hepatitis A virus strains identified in jogaejeot associated with outbreaks in Seoul,South Korea

Jogaejeot, seasoned Venerupis philippinarum, is a traditional Korean fermented food, and hepatitis A virus (HAV) can be transmitted through contaminated food, especially bivalve shellfish, causing acute gastroenteritis worldwide. Here, we carried out a phylogenetic analysis to identify and characterize HAV strains in jogaejeot samples associated with hepatitis A (HA) outbreaks in Seoul, South Korea, in 2019. The HAV strains were identified using blast and molecular analysis of the amplified HAV VP1-P2B genome region. The HAV strains identified in the five jogaejeot samples shared at least 99% sequence identity, were all classified as genotype IA and were most closely related to strains that are widespread in East Asia. These results support a link between the consumption of jogaejeot and the HA outbreaks observed in 2019 in Seoul. In addition, they indicate a need for more stringent enforcement of food safety regulations for the shellfish industry, especially against HAV, and the value of widespread vaccination.     

A viral mechanism in acute exacerbations of chronic type B hepatitis: Hepatitis B virus reinfection and subsequent reactivation of two viral strains

Chronic hepatitis B virus (HBV) infections are frequently associated with exacerbations of hepatitis of which the majority are due to reactivation of viral activity. Variation in a viral genome during persistent infection has been shown to be a possible cause for reactivation. In this study, we have found another possible mechanism. HBV in a patient with repeated exacerbations was isolated at six different times during follow-up and was characterized by polymerase chain reaction and DNA sequencing. The first episode of exacerbation was accompanied with increased replication of an HBV strain. The second episode, however, was associated with the sudden appearance of an HBV strain that displayed enough sequence variations to warrant the designation as a separate strain. The results suggested a reinfection event by another independent HBV. Subsequent exacerbations were then related to coactivation of both viral stains. These observations provide significant information toward understanding the acute exacerbations of chronic type B hepatitis.     

Hepatitis C virus NS5A protein interacts with lysine methyltransferase SET and MYND domain‐containing 3 and induces activator protein 1 activation

Hepatitis C virus (HCV) non‐structural protein 5A (NS5A) is a multifunctional protein that is involved in the HCV life cycle and pathogenesis. In this study, a host protein(s) interacting with NS5A by tandem affinity purification were searched for with the aim of elucidating the role of NS5A. An NS5A‐interacting protein, SET and MYND domain‐containing 3 (SMYD3), a lysine methyltransferase reportedly involved in the development of cancer, was identified. The interaction between NS5A and SMYD3 was confirmed in ectopically expressing, HCV RNA replicon‐harboring and HCV‐infected cells. The other HCV proteins did not bind to SMYD3. SMYD3 bound to NS5A of HCV genotypes 1b and 2a. Deletion mutational analysis revealed that domains II and III of NS5A (amino acids [aa] 250 to 447) and the MYND and N‐SET domains of SMYD3 (aa 1 to 87) are involved in the full extent of NS5A‐SMYD3 interaction. NS5A co‐localized with SMYD3 exclusively in the cytoplasm, thereby inhibiting nuclear localization of SMYD3. Moreover, NS5A formed a complex with SMYD3 and heat shock protein 90 (HSP90), which is a positive regulator of SMYD3. The intensity of binding between SMYD3 and HSP90 was enhanced by NS5A. Luciferase reporter assay demonstrated that NS5A significantly induces activator protein 1 (AP‐1) activity, this being potentiated by co‐expression of SMYD3 with NS5A. Taken together, the present results suggest that NS5A interacts with SMYD3 and induces AP‐1 activation, possibly by facilitating binding between HSP90 and SMYD3. This may be a novel mechanism of AP‐1 activation in HCV‐infected cells.     

Design, expression, and purification of a Flaviviridae polymerase using a high-throughput approach to facilitate crystal structure determination

Bovine viral diarrhea virus (BVDV) nonstructural protein 5B is an RNA-dependent RNA polymerase, essential for viral replication. Initial attempts to crystallize a soluble form of the 695-residue BVDV polymerase did not produce any crystals. Limited proteolysis, homology modeling, and mutagenesis data were used to aid the design of polymerase constructs that might crystallize more readily. Limited proteolysis of the polymerase with trypsin identified a domain boundary within the protein. Homology modeling of the polymerase, based on the structure of hepatitis C virus polymerase, indicated that the two polymerases share a 23% identical "core," although overall sequence identity is low. Eighty-four expression clones of the BVDV polymerase were designed by fine-sampling of chain termini at the boundaries of domain and of active truncated forms of the polymerase. The resulting constructs were expressed in Escherichia coli and purified using high-throughput methods. Soluble truncated proteins were subjected to crystallization trials in a 96-well format, and two of these proteins were successfully crystallized.     

Detection of a natural point mutation in Potato virus A that overcomes resistance to vascular movement in Nicandra physaloides., and studies on seed-transmissibility of the mutant virus

Isolate M of Potato virus A (PVA‐M; genus Potyvirus) is avirulent in Nicandra physaloides L. (family Solanaceae). The inoculated leaves are infected but no systemic infection is observed. Forty plants of ‘Black Pod’ (BP) and ‘Black Pod Alba’ (BPA), two variants of N. physaloides described in this study, were inoculated with PVA‐M. Two plants of BP and one plant of BPA were systemically infected. Mosaic, blistering and dark green islands developed on the systemically infected leaves, and flowers showed colour‐break symptoms. PVAprogeny were sequence‐characterised for the 6K2 protein and viral genome‐linked protein (VPg) encoding regions known to control the long distance movement of PVA in N. physaloides. All virus progeny (designated as PVA‐Mm) in the systemically infected leaves of the plants inoculated with PVA‐M contained only a single amino acid substitution (Vail 16Met) in the central part of VPg due to a nucleotide substitution G6033A, as compared to PVA‐M. Other PVA isolates that infected N. physaloides systemically also contained Metll6 in VPg. In a previous study using chimeric viruses, Metl16 in VPg was shown to be a major determinant for vascular movement of PVA in N. physaloides, and this study reveals that the mutation for Metl16 can occur in vivo during replication of the avirulent PVA‐M in infected plants. Immunolocalisation studies on BP and BPA plants showed that the pods (berries) and seed coat contained PVA‐Mm in the developing seeds, but no virus was detected in embryons. Up to 27% of the mature seeds contained PVA‐Mm but no transmission to seedlings was observed in a total of 450 seeds tested, and no test plants were infected following mechanical inoculation with extracts prepared from the seeds.     

神经氨酸酶、碱性聚合酶2及非结构蛋白1影响A型流感病毒致病力的分子机制研究进展

随着研究的不断深入,血凝素(HA)之外的其他蛋白在影响A型流感病毒的致病力甚至宿主特异性方面的重要作用逐渐受到关注。本文对神经氨酸酶(NA)、碱性聚合酶2(PB2)及非结构蛋白1(NS1)的相关进展作了综述,以期进一步阐明流感病毒的致病分子基础,并藉此探讨可能的宿主范围限定因素。     

Poly(A) tail affects equilibrium and thermodynamic behavior of tobacco etch virus mRNA with translation initiation factors eIF4F,eIF4B and PABP

We have investigated the effects of poly(A)-tail on binding of eIF4F, eIF4B and PABP with tobacco etch virus (TEV) IRES RNA. The fluorescence anisotropy data showed that the addition of poly(A)₂₀ increases the binding affinity of eIF4F·4B and eIF4F·PABP complexes to IRES RNA ~ 2- and 4-fold, respectively. However, the binding affinity of eIF4F with PK1 was enhanced ~ 11-fold with the addition of PABP, eIF4B, and poly(A)₂₀ together. Whereas, poly(A)₂₀ alone increases the binding affinity of eIF4F·4B·PABP with PK1 RNA about 3-fold, showing an additive effect rather than the large increase in affinity as shown for cap binding. Thermodynamic data showed that PK1 RNA binding to protein complexes in the presence of poly(A)₂₀ was enthalpy-driven and entropy-favorable. Poly(A)₂₀ decreased the entropic contribution 75% for binding of PK1 RNA to eIF4F·4B·PABP as compared to eIF4F alone, suggesting reduced hydrophobic interactions for complex formation and an overall conformational change. Overall, these results demonstrate the first direct effect of poly(A) on the equilibrium and thermodynamics of eIF4F and eIF4F·4B·PABP with IRES-RNA.