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New strategy attacks the ebola virus at a RNA level and stops viral replication.

Opening the door to potential treatments for the deadly Ebola virus, scientists have found that a protein made by the virus plays a role similar to that of a coat-check attendant.  The protein removes a protective coat from the virus’s genetic material, exposing the viral genome so that it can be copied, and then returns the coat, according to new research from Washington University, Icahn School of Medicine, University of Texas Southwestern, Texas Biomedical Research Institute and Baylor University.  The research, in cell cultures, showed that interfering with this process kills the virus.

As part of the current study, the researchers introduced rogue coat-check attendants into Ebola-infected cells. These rogue attendants carried a short chain of amino acids that forms the part of the protein that removes the coat. But they lacked the ability to return the coat, disrupting the emergence of newly created viruses from infected cells. Consequently, the virus did not survive.

This coat-check protein, known as VP35, has a great deal of potential as a new target for Ebola treatments state the team.  If the medical community can block this process, they can stop Ebola infection by blocking viral replication.  The opensource study is published in the journal Cell Reports.

The Ebola outbreak that began last year in West Africa has infected nearly 25,000 people and killed more than 10,000, according to the Centers for Disease Control and Prevention.  Ebola and other viruses like it are made of a single strand of RNA, a genetic material closely related to DNA. Higher organisms use RNA to copy protein-building instructions from their DNA, but Ebola stores such instructions, the virus’s genetic self, directly in RNA.  RNA is less stable than DNA and can set off immune defenses that destroy viruses. So Ebola keeps its RNA covered with a protective coat called the nucleoprotein, explain the team.

To replicate, however, the virus has to partially remove the nucleoprotein and expose its RNA to the viral copying machinery. The team have spent the past seven years studying the role of VP35, a viral protein involved in the replication process.

One of the major challenges was that the part of VP35 involved in this interaction is an intrinsically disordered peptide state the team, adding that this means that it may not take on a definite structure until it binds to another protein. That made structural studies of VP35 difficult because the structure, which plays a critical role in determining function, doesn’t form without its specific binding partner.

The researchers showed that VP35 binds to the virus’s nucleoprotein, which forms part of the protective coat worn by the virus’ RNA. The current study showed that this binding removes the nucleoprotein from the viral RNA prior to replication. And while the viral RNA is being copied, VP35 keeps newly synthesized nucleoproteins from attaching to other RNA in the host cell.

New copies of the virus require new protein coats. So VP35 also ensures that new nucleoproteins, made by the host cell’s protein-making machinery, bind only to Ebola RNA, allowing the virus to complete replicating. The team surmise that disabling or disrupting VP35 could stop the virus in its tracks.

Source:  Washington University School of Medicine in St. Louis

During viral RNA synthesis, Ebola virus (EBOV) nucleoprotein (NP) alternates between an RNA-template-bound form and a template-free form to provide the viral polymerase access to the RNA template. In addition, newly synthesized NP must be prevented from indiscriminately binding to noncognate RNAs. Here, we investigate the molecular bases for these critical processes. We identify an intrinsically disordered peptide derived from EBOV VP35 (NPBP, residues 20–48) that binds NP with high affinity and specificity, inhibits NP oligomerization, and releases RNA from NP-RNA complexes in vitro. The structure of the NPBP/ΔNPNTD complex, solved to 3.7 Å resolution, reveals how NPBP peptide occludes a large surface area that is important for NP-NP and NP-RNA interactions and for viral RNA synthesis. Together, our results identify a highly conserved viral interface that is important for EBOV replication and can be targeted for therapeutic development.  An Intrinsically Disordered Peptide from Ebola Virus VP35 Controls Viral RNA Synthesis by Modulating Nucleoprotein-RNA Interactions.  Amarasinghe et al 2015.
During viral RNA synthesis, Ebola virus (EBOV) nucleoprotein (NP) alternates between an RNA-template-bound form and a template-free form to provide the viral polymerase access to the RNA template. In addition, newly synthesized NP must be prevented from indiscriminately binding to noncognate RNAs. Here, we investigate the molecular bases for these critical processes. We identify an intrinsically disordered peptide derived from EBOV VP35 (NPBP, residues 20–48) that binds NP with high affinity and specificity, inhibits NP oligomerization, and releases RNA from NP-RNA complexes in vitro. The structure of the NPBP/ΔNPNTD complex, solved to 3.7 Å resolution, reveals how NPBP peptide occludes a large surface area that is important for NP-NP and NP-RNA interactions and for viral RNA synthesis. Together, our results identify a highly conserved viral interface that is important for EBOV replication and can be targeted for therapeutic development. An Intrinsically Disordered Peptide from Ebola Virus VP35 Controls Viral RNA Synthesis by Modulating Nucleoprotein-RNA Interactions. Amarasinghe et al 2015.

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