title: Conserved glycine residues in the fusion peptide of the paramyxovirus fusion protein regulate activation of the native state.
abstract: Hydrophobic fusion peptides (FPs) are the most highly conserved regions of class I viral fusion-mediating glycoproteins (vFGPs). FPs often contain conserved glycine residues thought to be critical for forming structures that destabilize target membranes. Unexpectedly, a mutation of glycine residues in the FP of the fusion (F) protein from the paramyxovirus simian parainfluenza virus 5 (SV5) resulted in mutant F proteins with hyperactive fusion phenotypes (C. M. Horvath and R. A. Lamb, J. Virol. 66:2443-2455, 1992). Here, we constructed G3A and G7A mutations into the F proteins of SV5 (W3A and WR isolates), Newcastle disease virus (NDV), and human parainfluenza virus type 3 (HPIV3). All of the mutant F proteins, except NDV G7A, caused increased cell-cell fusion despite having slight to moderate reductions in cell surface expression compared to those of wild-type F proteins. The G3A and G7A mutations cause SV5 WR F, but not NDV F or HPIV3 F, to be triggered to cause fusion in the absence of coexpression of its homotypic receptor-binding protein hemagglutinin-neuraminidase (HN), suggesting that NDV and HPIV3 F have stricter requirements for homotypic HN for fusion activation. Dye transfer assays show that the G3A and G7A mutations decrease the energy required to activate F at a step in the fusion cascade preceding prehairpin intermediate formation and hemifusion. Conserved glycine residues in the FP of paramyxovirus F appear to have a primary role in regulating the activation of the metastable native form of F. Glycine residues in the FPs of other class I vFGPs may also regulate fusion activation.
authors.affiliation: Howard Hughes Medical Institute, Northwestern University, 2205 Tech Dr., Evanston, IL 60208-3500, USA.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Russell
authors.forename: Theodore S
authors.initials: TS
authors.lastname: Jardetzky
authors.forename: Robert A
authors.initials: RA
authors.lastname: Lamb
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002459:Cell Fusion; D002460:Cell Line; D002522:Chlorocebus aethiops; D017124:Conserved Sequence; D006224:Cricetinae; D015967:Gene Expression Regulation, Viral; D015726:Giant Cells; D005998:Glycine; D006801:Humans; D008561:Membrane Fusion; D008969:Molecular Sequence Data; D009154:Mutation; D009522:Newcastle disease virus / Q000472:pathogenicity; D010224:Parainfluenza Virus 3, Human / Q000472:pathogenicity; D018098:Paramyxovirinae / Q000472:pathogenicity*; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D019213:Rubulavirus / Q000472:pathogenicity; D014709:Vero Cells; D014760:Viral Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D010455:Peptides; D014760:Viral Fusion Proteins; C072983:F protein, parainfluenza virus 3; D005998:Glycine