title: Quantitative analysis of Nipah virus proteins released as virus-like particles reveals central role for the matrix protein.
abstract: BACKGROUND
  Nipah virus (NiV) is an emerging paramyxovirus distinguished by its ability to cause fatal disease in both animal and human hosts. Together with Hendra virus (HeV), they comprise the genus Henipavirus in the Paramyxoviridae family. NiV and HeV are also restricted to Biosafety Level-4 containment and this has hampered progress towards examining details of their replication and morphogenesis. Here, we have established recombinant expression systems to study NiV particle assembly and budding through the formation of virus-like particles (VLPs).
  
  
  RESULTS
  When expressed by recombinant Modified Vaccinia virus Ankara (rMVA) or plasmid transfection, individual NiV matrix (M), fusion (F) and attachment (G) proteins were all released into culture supernatants in a membrane-associated state as determined by sucrose density gradient flotation and immunoprecipitation. However, co-expression of F and G along with M revealed a shift in their distribution across the gradient, indicating association with M in VLPs. Protein release was also altered depending on the context of viral proteins being expressed, with F, G and nucleocapsid (N) protein reducing M release, and N release dependent on the co-expression of M. Immunoelectron microscopy and density analysis revealed VLPs that were similar to authentic virus. Differences in the budding dynamics of NiV proteins were also noted between rMVA and plasmid based strategies, suggesting that over-expression by poxvirus may not be appropriate for studying the details of recombinant virus particle assembly and release.
  
  
  CONCLUSIONS
  Taken together, the results indicate that NiV M, F, and G each possess some ability to bud from expressing cells, and that co-expression of these viral proteins results in a more organized budding process with M playing a central role. These findings will aid our understanding of paramyxovirus particle assembly in general and could help facilitate the development of a novel vaccine approach for henipaviruses.
authors.affiliation: Department of Microbiology and Immunology, Uniformed Services University, Bethesda, Maryland 20814, USA. jpatch@usuhs.mil
authors.forename: Jared R
authors.initials: JR
authors.lastname: Patch
authors.forename: Gary
authors.initials: G
authors.lastname: Crameri
authors.forename: Lin-Fa
authors.initials: LF
authors.lastname: Wang
authors.forename: Bryan T
authors.initials: BT
authors.lastname: Eaton
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Broder
mesh_terms: D000818:Animals; D002460:Cell Line; D002642:Chick Embryo; D002522:Chlorocebus aethiops; D006801:Humans; D045405:Nipah Virus / Q000378:metabolism*; D019590:Nucleocapsid Proteins / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011995:Recombination, Genetic; D014162:Transfection; D014616:Vaccinia virus / Q000235:genetics / Q000378:metabolism; D014709:Vero Cells; D014759:Viral Envelope Proteins / Q000378:metabolism; D014760:Viral Fusion Proteins / Q000378:metabolism; D014763:Viral Matrix Proteins / Q000378:metabolism*; D014771:Virion / Q000378:metabolism*; D019065:Virus Assembly
chemical_list: D019590:Nucleocapsid Proteins; D014759:Viral Envelope Proteins; D014760:Viral Fusion Proteins; D014763:Viral Matrix Proteins; C116204:attachment protein G