Signal peptide and helical bundle domains of virulent canine distemper virus fusion protein restrict fusogenicity.
Persistence in canine distemper virus (CDV) infection is correlated with very limited cell-cell fusion and lack of cytolysis induced by the neurovirulent A75/17-CDV compared to that of the cytolytic Onderstepoort vaccine strain. We have previously shown that this difference was at least in part due to the amino acid sequence of the fusion (F) protein (P. Plattet, J. P. Rivals, B. Zuber, J. M. Brunner, A. Zurbriggen, and R. Wittek, Virology 337:312-326, 2005). Here, we investigated the molecular mechanisms of the neurovirulent CDV F protein underlying limited membrane fusion activity. By exchanging the signal peptide between both F CDV strains or replacing it with an exogenous signal peptide, we demonstrated that this domain controlled intracellular and consequently cell surface protein expression, thus indirectly modulating fusogenicity. In addition, by serially passaging a poorly fusogenic virus and selecting a syncytium-forming variant, we identified the mutation L372W as being responsible for this change of phenotype. Intriguingly, residue L372 potentially is located in the helical bundle domain of the F(1) subunit. We showed that this mutation drastically increased fusion activity of F proteins of both CDV strains in a signal peptide-independent manner. Due to its unique structure even among morbilliviruses, our findings with respect to the signal peptide are likely to be specifically relevant to CDV, whereas the results related to the helical bundle add new insights to our growing understanding of this class of F proteins. We conclude that different mechanisms involving multiple domains of the neurovirulent A75/17-CDV F protein act in concert to limit fusion activity, preventing lysis of infected cells, which ultimately may favor viral persistence.
Department of Clinical Veterinary Medicine, Bremgartenstrasse 109a, 3001 Bern, Switzerland.
Philippe
P
Plattet
Pascal
P
Cherpillod
Dominique
D
Wiener
Ljerka
L
Zipperle
Marc
M
Vandevelde
Riccardo
R
Wittek
Andreas
A
Zurbriggen
D000818:Animals; D004217:Distemper Virus, Canine / Q000737:chemistry / Q000472:pathogenicity*; D004285:Dogs; D020125:Mutation, Missense; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D014760:Viral Fusion Proteins / Q000737:chemistry* / Q000235:genetics; D014774:Virulence
D021382:Protein Sorting Signals; D014760:Viral Fusion Proteins