Influence of RNA binding on the structure and functionality of Borna disease virus matrix protein
P. Kolenko1, P. Dautel1, R. Novotny2, A. Martin2, Ch. Parthier1, M. Schwemmle2, M.T. Stubbs1
1Institut für Biochemie und Biotechnologie, Martin-Luther Universität, Kurt-Mothes-Straße 3, 06 120 Halle (Saale), Germany
2Institut für Virologie, Universität Freiburg, Hermann-Herder-Straße 11, 79 104 Freiburg, Germany
Borna disease virus (BDV) is the causative agent for Borna disease, a non-cytolytic, persistent infection of the central nervous system detected originally among horses in Borna, Germany. BDV has been used as a model system to investigate and understand persistent viral infections of the brain. Known hosts of BDV range from rodents to non-human primates  and recently it was shown that BDV is responsible for the first endogenized non-retroviral virus-derived elements in mammalian genomes . BDV is the only member of the family of Bornaviridae that belongs to the order Mononegavirales, which includes among others the viruses Marburg, Ebola and Rabies.
BDV has the smallest genome among all known negative stranded non-segmented RNA viruses, with a size of 8.9 kb, encoding for six proteins . The matrix protein of BDV (BDVM), a 16.2 kDa protein that forms either a stable homotetramer or –octamer , is associated with virus assembly and budding and may also be associated with the regulation of the viral ribonucleoprotein activity . We have recently shown that BDVM binds single stranded RNA , as does the matrix protein VP40 of the Ebola virus .
To further investigate the structural and functional influence of RNA binding on BDVM, we mutated the specific RNA binding site, creating the variant BDVM H112W. This variant shows a previously unknown dodecameric oligomerization state and altered RNA binding abilities. More variants of BDVM were created to anticipate the new oligomerization state of BDVM H112W, giving a more detailed insight concerning the oligomerization state and RNA binding abilities of BDVM. An additional cell-based investigation of recombinant viruses harbouring these mutations showed potent growth attenuation and an atypical cytoplasmic accumulation in Vero cells.
Taken together the structural and functional data indicates that RNA binding and appropriate oligomerization of BDVM is required for proper viral growth.
The work on this project was supported by the Graduiertenkolleg 1026 “Conformational transitions in macromolecular interactions” of the Deutsche Forschungsgemeinschaft.
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