The C-terminal amyloidogenic peptide contributes to self-assembly of Avibirnavirus viral protease.

Unlike other viral protease, Avibirnavirus infectious bursal disease virus (IBDV)-encoded viral protease VP4 forms unusual intracellular tubule-like structures during viral infection. However, the formation mechanism and potential biological functions of intracellular VP4 tubules remain largely elusive. Here, we show that VP4 can assemble into tubules in diverse IBDV-infected cells. Dynamic analysis show that VP4 initiates the assembly at early stage of IBDV infection, and gradually assembles into larger size of fibrils within the cytoplasm and nucleus. Intracellular assembly of VP4 doesn't involve the host cytoskeleton, other IBDV-encoded viral proteins or vital subcellular organelles. Interestingly, the last C-terminal hydrophobic and amyloidogenic stretch (238)YHLAMA(243) with two "aggregation-prone" alanine residues was found to be essential for its intracellular self-assembly. The assembled VP4 fibrils show significantly low solubility, subsequently, the deposition of highly assembled VP4 structures ultimately deformed the host cytoskeleton and nucleus, which was potentially associated with IBDV lytic infection. Importantly, the assembly of VP4 significantly reduced the cytotoxicity of protease activity in host cells which potentially prevent the premature cell death and facilitate viral replication. This study provides novel insights into the formation mechanism and biological functions of the Avibirnavirus protease-related fibrils.

Ginseng stem-leaf saponins (GSLS) and mineral oil act synergistically to enhance the immune responses to vaccination against foot-and-mouth disease in mice.

Saponins extracted from ginseng stems and leaves (GSLS) as well as the synergistic effect between GSLS and oil emulsion were investigated for their adjuvant effects on the immune responses of mice to vaccination against foot-and-mouth disease virus (FMDV) serotype Asia 1. In experiment A, ICR mice were subcutaneously immunized twice with FMDV antigen with or without GSLS (0, 1, 5, 10 and 20 microg) at 3 week intervals. Highest FMDV-specific IgG level was observed 2 weeks after the boosting in mice immunized with FMDV antigen plus 10 microg of GSLS. In experiment B, mice were subcutaneously injected with FMDV antigen with or without GSLS (10 microg), or in oil emulsion with or without GSLS (10 microg) on days 1 and 21. Results indicated that when co-administered with a mixture of oil and GSLS, FMDV antigen induced significantly higher IgG titer and IgG1, IgG2a, IgG2b and IgG3 responses, production of IFN-gamma (Th1 cytokine) and IL-5 (Th2 cytokine) by splenocytes, as well as T and B lymphocyte proliferation in response to Con A and LPS than when FMDV antigen was used alone or mixed with either GSLS or oil. This suggests that GSLS and oil adjuvant synergistically promote both Th1 and Th2 immune responses. As protection against FMDV requires both cellular and humoral immune responses, the combined effects of GSLS and oil deserve further study in other animals such as cattle and pigs in order to induce effective immunity against FMDV infection.