title: Conserved leucine residue in the head region of morbillivirus fusion protein regulates the large conformational change during fusion activity.
abstract: Paramyxovirus cell entry is controlled by the concerted action of two viral envelope glycoproteins, the fusion (F) and the receptor-binding (H) proteins, which together with a cell surface receptor mediate plasma membrane fusion activity. The paramyxovirus F protein belongs to class I viral fusion proteins which typically contain two heptad repeat regions (HR). Particular to paramyxovirus F proteins is a long intervening sequence (IS) located between both HR domains. To investigate the role of the IS domain in regulating fusogenicity, we mutated in the canine distemper virus (CDV) F protein IS domain a highly conserved leucine residue (L372) previously reported to cause a hyperfusogenic phenotype. Beside one F mutant, which elicited significant defects in processing, transport competence, and fusogenicity, all remaining mutants were characterized by enhanced fusion activity despite normal or slightly impaired processing and cell surface targeting. Using anti-CDV-F monoclonal antibodies, modified conformational F states were detected in F mutants compared to the parental protein. Despite these structural differences, coimmunoprecipitation assays did not reveal any drastic modulation in F/H avidity of interaction. However, we found that F mutants had significantly enhanced fusogenicity at low temperature only, suggesting that they folded into conformations requiring less energy to activate fusion. Together, these data provide strong biochemical and functional evidence that the conserved leucine 372 at the base of the HRA coiled-coil of F(wt) controls the stabilization of the prefusogenic state, restraining the conformational switch and thereby preventing extensive cell-cell fusion activity.
authors.affiliation: Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Bern, Bern, Switzerland. philippe.plattet@itn.unibe.ch
authors.forename: Philippe
authors.initials: P
authors.lastname: Plattet
authors.forename: Johannes P M
authors.initials: JP
authors.lastname: Langedijk
authors.forename: Ljerka
authors.initials: L
authors.lastname: Zipperle
authors.forename: Marc
authors.initials: M
authors.lastname: Vandevelde
authors.forename: Claes
authors.initials: C
authors.lastname: Orvell
authors.forename: Andreas
authors.initials: A
authors.lastname: Zurbriggen
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000911:Antibodies, Monoclonal; D000956:Antigens, Viral / Q000737:chemistry; D002522:Chlorocebus aethiops; D017124:Conserved Sequence; D004217:Distemper Virus, Canine / Q000737:chemistry* / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D004285:Dogs; D000939:Epitopes / Q000737:chemistry; D007930:Leucine / Q000737:chemistry; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics; D014709:Vero Cells; D014760:Viral Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D053586:Virus Internalization
chemical_list: D000911:Antibodies, Monoclonal; D000956:Antigens, Viral; D000939:Epitopes; D011994:Recombinant Proteins; D014760:Viral Fusion Proteins; D014764:Viral Proteins; C076619:F protein, Phocine distemper virus; D007930:Leucine