== In consideration of the crystal structures of the NDV and parainfluenza virus 5 (PIV5) F proteins (3,27), several residues located on the head and stalk of the NDV F protein were mutated

== In consideration of the crystal structures of the NDV and parainfluenza virus 5 (PIV5) F proteins (3,27), several residues located on the head and stalk of the NDV F protein were mutated. The N211A, L461A, I463A, and I463F mutants showed a hyperfusogenic phenotype both in syncytium and in dye transfer assays. The four mutants promoted fusion more efficiently at lower temperatures than the wild type did, meaning they probably experienced lower energy requirements for activation. Moreover, the N211A, I463A, and I463F mutants exhibited hemagglutinin-neuraminidase (HN)-impartial activity when influenza computer virus hemagglutinin (HA) was coexpressed as an attachment protein. The data are discussed in terms of alterations of the refolding pathway and/or the stability of the prefusion and fusion conformations. Newcastle disease computer virus (NDV) is an avian enveloped computer virus belonging to the familyParamyxoviridae. Two viral membrane-associated proteins are responsible for the entry of the computer virus into the host cell: they are hemagglutinin-neuraminidase (HN), a receptor-binding protein that interacts with sialoglycoconjugates at the cell surface, and F, a trimeric class I fusion protein that, upon activation, triggers the fusion of the viral and target membranes. F protein is usually activated after the attachment of its homotypic HN protein to the proper receptor; however, how HN activates F is not well comprehended. F protein is usually synthesized as an inactive precursor, F0, that is activated by proteolytic cleavage to the disulfide-linked F1-F2fusion-competent form (Fig.1) (10). The crystal structures of several paramyxoviral fusion proteins, in both the prefusion and postfusion conformations (3,26,27), have revealed that these proteins undergo major conformational changes, from a metastable conformation to a highly stable, postfusion form. Several regions in the ectodomain Atipamezole of class I viral fusion proteins are involved in these conformational conversions, including a hydrophobic fusion peptide at the N terminus of the F1 protein and two hydrophobic heptad repeat motifs, HRA and HRB, located at its N and C termini, respectively (Fig.1). In the prefusion form, HRB shows a triple-stranded coiled-coil conformation forming the stalk of the mushroom-like protein (3,19,27). Its globular head contains three domains, DI to DIII (Fig.1), with the base of the head being formed by the DI and DII domains, with residues predominantly located between HRA and HRB. The top of the head is usually created by DIII, consisting mainly of HRA and the fusion peptide, located on the side of the head sequestered between adjacent subunits. In this prefusion state, HRA is usually folded as two antiparallel -strands and four (h1 to h4) helices (27) (observe Fig.6). The DIII domain name undergoes major structural changes from your prefusion to the final postfusion conformation. HRA refolds as Atipamezole an -helix, propelling the fusion peptide into the target membrane and generating a prehairpin intermediate (observe Fig.6). The final, stable conformation consists of a six-helical bundle (6HB), comprising a dimer of trimers in which the trimeric HRA coiled coil forms the core, packed along the outside by three antiparallel HRB -helices (1,3,19,27). Atipamezole == FIG. 1. == Schematic representation of the structure of the NDV fusion protein. (A) Domain structure of F protein (27). (B) Locations of the fusion peptide, HR regions, and sequences analyzed. Mutated residues are indicated in strong. == FIG. 6. == Plan of conformational changes in HRA from prefusion to postfusion state. (A) Ribbon model of Atipamezole PIV5 F protein in its metastable prefusion conformation (PDB accession number 2b9b) (27), showing some residues (named in white) from Mouse monoclonal to MYL3 your A subunit and the corresponding residues in the NDV F protein (named in yellow). Subunits B and C are depicted in gray for clarity. (B) In the metastable, prefusion conformation, HRA is usually folded as a spring-loaded mixture of -helices, turns, and -strands, comprising 11 segments in the DIII head domain of the trimer (27). (C) After fusion, HRA is usually presented as a single long helix that allows the fusion peptide to be buried in the target membrane. The approximate Atipamezole positions of HRC and the core.