Identification of determinants that mediate binding between Tembusu virus and the cellular receptor heat shock protein A9

Self-Assembled Nanoparticles with E Protein Domains I and II of Duck Tembusu Virus Can Induce a More Comprehensive Immune Response Against the Duck Tembusu Virus Challenge

Duck Tembusu virus (DTMUV) is a pathogenic flavivirus that causes a substantial drop in egg production and severe neurological disorders in domestic waterfowl. Self-assembled ferritin nanoparticles with E protein domains I and II (EDI-II) of DTMUV (EDI-II-RFNp) were prepared, and its morphology was observed. Two independent experiments were conducted. First, Cherry Valley ducks aged 14 days were vaccinated with EDI-II-RFNp, EDI-II, and phosphate buffered solution (PBS, pH 7.4), and special and virus neutralization (VN) antibodies, interleukin 4 (IL-4) and interferon gamma (IFN-γ) in serum, and lymphocyte proliferation were detected. Second, the vaccinated ducks with EDI-II-RFNp, EDI-II, and PBS were injected with virulent DTMUV, clinical signs at 7 days postinfection (dpi) were observed, and mRNA levels of DTMUV in the lungs, liver, and brain at 7 and 14 dpi were detected. The results showed near-spherical nanoparticles EDI-II-RFNp with a 16.46 ± 4.70 nm diameters. The levels of specific and VN antibodies, IL-4 and IFN-γ, and lymphocyte proliferation in the EDI-II-RFNp group were significantly higher than those in the EDI-II and PBS groups. In the DTMUV challenge test, clinical signs and mRNA levels in tissue were used to evaluate protection of EDI-II-RFNp. EDI-II-RFNp-vaccinated ducks showed milder clinical signs and lower levels of DTMUV RNA in the lungs, liver, and brain. These results indicate that EDI-II-RFNp effectively protects ducks against the DTMUV challenge and could be a vaccine candidate to provide an effective and safe method for preventing and controlling DTMUV infection.

The key amino acids of E protein involved in early flavivirus infection: viral entry

Flaviviruses are enveloped viruses that infect multiple hosts. Envelope proteins are the outermost proteins in the structure of flaviviruses and mediate viral infection. Studies indicate that flaviviruses mainly use envelope proteins to bind to cell attachment receptors and endocytic receptors for the entry step. Here, we present current findings regarding key envelope protein amino acids that participate in the flavivirus early infection process. Among these sites, most are located in special positions of the protein structure, such as the α-helix in the stem region and the hinge region between domains I and II, motifs that potentially affect the interaction between different domains. Some of these sites are located in positions involved in conformational changes in envelope proteins. In summary, we summarize and discuss the key envelope protein residues that affect the entry process of flaviviruses, including the process of their discovery and the mechanisms that affect early infection.

Tembusu virus enters BHK-21 cells through a cholesterol-dependent and clathrin-mediated endocytosis pathway

Tembusu virus (TMUV) is a newly emerging flavivirus and has caused significant economic loss to the poultry industry in China. To date, the entry of TMUV into host cells remains poorly understood. Here, the mechanism of TMUV entry into BHK-21 cells was investigated. The depletion of cellular cholesterol by methyl-β-cyclodextrin led to a significant decline in the titers and RNA levels of the infectious TMUV. This reduction was restored by supplementation of exogenous cholesterol. Membrane cholesterol depletion mainly blocked viral internalization but not attachment. However, viral infection was unaffected by genistein treatment or caveolin-1 silencing by small interfering RNA. In addition, clathrin-mediated endocytosis might be utilized in TMUV entry given that the viral infection was inhibited by knockdown of clathrin heavy chain and treatment of chlorpromazine (CPZ). Moreover, the number of internalized virus particles decreased under CPZ treatment. Dynasore inhibited TMUV entry suggesting a role for dynamin. Our results reveal that TMUV entry into BHK-21 cells is dependent on cholesterol, clathrin and dynamin but not caveolae.