The data show that this hyperfusogenic F-L179V virus induces greater morbidity and mortality than the wild-type virus while the hypofusogenic and attenuated F-K180Q virus causes much less. == FIG. and fusogenicity. In DBA/2 mice, the hyperfusogenic F-L179V computer virus induced greater morbidity and mortality than wild-type computer virus, while the attenuated F-K180Q computer virus was much less pathogenic. During the first week of contamination, computer virus replication and inflammation in the lungs were comparable for wild-type and F-L179V viruses. After approximately 1 week of contamination, the clearance of F-L179V computer virus was delayed, and more considerable interstitial inflammation and necrosis were observed in the lungs, affecting entire lobes of the lungs and having significantly greater numbers of syncytial cell masses in alveolar spaces on day 10. On the other Melphalan hand, the slower-growing F-K180Q computer virus caused much less considerable inflammation than wild-type computer virus, presumably due to its reduced replication rate, and did not cause observable syncytium formation in the lungs. Overall, the results show that residues in the heptad repeat A region of the F protein modulate the virulence of Sendai computer virus in mice by influencing both the spread and clearance of the computer virus and the extent and severity of inflammation. An understanding of how the F protein contributes to contamination and inflammation in vivo may assist in the development of antiviral therapies against respiratory paramyxoviruses. Sendai computer virus (SeV), a murine parainfluenza computer virus (PIV), belongs to the genusRespiroviruswithin the familyParamyxoviridae(33). Sendai computer virus is the murine counterpart of human parainfluenza computer virus 1 (HPIV1), and these two viruses share high sequence homology and antigenic cross-reactivity (23,38,58). Melphalan Both Sendai computer virus and HPIV1 cause respiratory diseases in their hosts that range from mild to severe, with the greatest morbidity and mortality occurring in immunocompromised hosts (3,17). In pediatric medicine, HPIV1 is an important cause of bronchiolitis, pneumonia, and laryngotracheobronchitis, or croup (11). Other members of the genusRespirovirusinclude human and bovine forms of PIV3 (30). Like other paramyxoviruses, Sendai computer virus is an enveloped, nonsegmented, negative-strand RNA computer virus that invades host cells by fusion (F) protein-mediated membrane fusion at the plasma membrane (33). The receptor binding protein for Sendai computer virus, as well as the other parainfluenza viruses, is the hemagglutinin-neuraminidase (HN) protein. During viral access, the Rabbit Polyclonal to C/EBP-alpha (phospho-Ser21) HN protein binds sialic acid-containing receptors around the surfaces of host cells and then triggers the F protein to refold and cause membrane fusion (34,40). Paramyxovirus replication occurs in the cytoplasm of infected cells, where the viral nucleocapsid is usually formed by the encapsidation of the viral genome with the viral nucleoprotein (N), phosphoprotein (P), and the large RNA-dependent RNA-polymerase (L) protein (33). The assembly and budding of infectious parainfluenza virions from your plasma membrane are mediated largely by the matrix (M) protein, which interacts with the viral nucleocapsid and the cytoplasmic tails of the HN and F proteins (56,63). The paramyxovirus F protein mediates both virus-cell fusion and cell-cell fusion. Much like other class I viral fusion proteins, paramyxovirus F proteins are expressed around the surfaces of infected cells and virions as trimers that are caught in metastable (high energy) conformations (29,54,71,73). In order to become activated for membrane fusion, uncleaved F0precursor protein trimers must be cleaved into a fusion-capable complex created by F1and F2subunits (55). Field isolates of Sendai computer virus that have a monobasic cleavage site are cleavage activated by tryptase Clara secreted from respiratory epithelial cells (32,69) while the pantropic F1-R laboratory isolate of Sendai computer virus has a mutated cleavage site and is cleaved by more ubiquitously expressed proteases (41,67). Paramyxovirus F proteins have several regions involved in F protein conformational changes during membrane fusion: a hydrophobic fusion peptide, two 4-3 heptad repeat regions (designated heptad repeat A [HRA] and HRB), a Melphalan transmembrane domain name, and a cytoplasmic tail. The prefusion form of the PIV5 F0protein has a mushroom-like shape formed by a large globular head attached to a rod-like stalk created by the HRB region (76). Upon triggering by the HN protein, the HRB region dissociates, the HRA region springs into a coiled coil, and the fusion peptide is usually inserted into the target membrane (52). Membrane fusion is usually catalyzed by the formation of a coiled-coil hairpin structure (2,7,75,78), created by the HRA and HRB regions, that juxtaposes the membrane-interacting fusion peptide and transmembrane domains (52). We recently performed a mutational analysis on a 10-residue sequence in the HRA region of the Sendai computer virus F protein (37) that forms a -strand-turn–helix structure in the prefusion conformation and a part of a triple-stranded coiled coil in the hairpin conformation (75,76). The mutated residues were found to play important functions in regulating the activation and membrane fusion activity of the Sendai computer virus F protein, showing that F protein refolding is usually regulated by residues that undergo dramatic changes in secondary and tertiary structure between the prefusion and hairpin conformations. Upon triggering by the HN protein, cell surface-expressed F protein trimers mediate cell-cell fusion (syncytium formation).
