Newcastle disease virus (NDV), an avian paramyxovirus, causes Newcastle disease (ND) which is a highly contagious and fatal viral disease affecting poultry and most species of birds. The fusion (F) protein of NDV mediates membrane fusion, which is essential to the processes of viral entry, replication, and dissemination. Although several domains of NDV F are known to have important effects on regulating the membrane fusion activity, the role of the region around domain III (DIII) and domain I (DI) still remains ill-defined. Site-directed mutagenesis was utilized to change the conserved amino acids at 269, 274, 277, 286, 287, 290, 295, and 297 to alanine in order to investigate the effects of these conserved amino acids around the DIII and DI linker region of the NDV F protein on fusion activity. It was found that five of these substitutions almost abolished fusion activity except for mutants I269A, Q286A, and N297A, which showed 57.1%, 161.1%, and 97.7% of the wt F level, respectively. Four (I274A, D277A, V287A, and P290A) of these five mutants likely result in interfering with folding or transporting of the molecule since these proteins were minimally expressed at the cell surface, formed aggregates, or not proteolytically cleaved. However, mutant L295A almost abolished fusion activity even with a similar level of cell surface expression. These data indicated that conserved amino acids around the DIII-DI linker region are critical for the folding of the F protein and have an important influence on fusion activity.

Background: Sepsis frequently occurs in patients after infection and is highly associated with death. Septic encephalopathy is characterized by dysfunction of the central nervous system, of which the root cause is a systemic inflammatory response. Sepsis-associated encephalopathy is a severe disease that frequently occurs in children, resulting in high morbidity and mortality. Objectives: In the present study, we aim to investigate the neuroprotective mechanism of ginsenoside Rg1 in response to septic encephalopathy. Methods: Effects of ginsenoside Rg1 on septic encephalopathy were determined by cell viability, cytotoxicity, ROS responses, and apoptosis assays and histological examination of brain. Inflammatory activities were evaluated by expression levels of IL-1β, IL-6, IL-10, TNF-α, and MCP-1 using qPCR and ELISA. Activities of signaling pathways in inflammation were estimated by the production of p-Erk1/2/Erk1/2, p-JNK/JNK, p-p38/p38, p-p65/p65, and p-IkBα/IkBα using western blot. Results: LPS simulation resulted in a significant increase in cytotoxicity, ROS responses, and apoptosis and a significant decrease in cell viability in CTX TNA2 cells, as well as brain damage in rats. Moreover, the production of IL-1β, IL-6, IL-10, TNF-α, and MCP-1 was significantly stimulated both in CTX TNA2 cells and in the brain, which confirmed the establishment of vitro and in vivo models of septic encephalopathy. The damage and inflammatory responses induced by LPS were significantly decreased by treatment with Rg1. Western blot analyses indicated Rg1 significantly decreased the production of p-Erk1/2/Erk1/2, p-JNK/JNK, p-p38/p38, p-p65/p65, and p-IkBα/IkBα in LPS-induced CTX TNA2 cells and in the brain. Conclusions: These findings suggested that Rg1 inhibited the activation of NF-κB and MAPK signaling pathways, which activate the production of proinflammatory cytokines and chemokines. The findings of this study suggest that ginsenoside Rg1 is a candidate treatment for septic encephalopathy.

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Human parainfluenza virus type 3 (hPIV3) is an important respiratory pathogen that causes the majority of viral pneumonia of infants and young children. hPIV3 can infect host cells through the synergistic action of hemagglutinin-neuraminidase (HN) protein and the homotypic fusion (F) protein on the viral surface. HN protein plays a variety of roles during the virus invasion process, such as promoting viral particles to bind to receptors, cleaving sialic acid, and activating the F protein. Crystal structure research shows that HN tetramer adopted a "heads-down" conformation, at least two heads dimmer on flank of the four-helix bundle stalk, which forms a symmetrical interaction interface. The stalk region determines interactions and activation of F protein in specificity, and the heads in down position statically shield these residues. In order to make further research on the function of these amino acids at the hPIV3 HN stalk/head interface, fifteen mutations (8 sites from stalk and 7 sites from head) were engineered into this interface by site-directed mutagenesis in this study. Alanine substitution in this region of hPIV3 HN had various effects on cell fusion promotion, receptor binding, and neuraminidase activity. Besides, L151A also affected surface protein expression efficiency. Moreover, I112A, D120A, and R122A mutations of the stalk region that were masked by global head in down position had influence on the interaction between F and HN proteins.