Virology. Mutation rate and genotype variation of Ebola virus from Mali case sequences

The occurrence of Ebola virus (EBOV) in West Africa during 2013-2015 is unprecedented. Early reports suggested that in this outbreak EBOV is mutating twice as fast as previously observed, which indicates the potential for changes in transmissibility and virulence and could render current molecular diagnostics and countermeasures ineffective. We have determined additional full-length sequences from two clusters of imported EBOV infections into Mali, and we show that the nucleotide substitution rate (9.6 × 10(-4) substitutions per site per year) is consistent with rates observed in Central African outbreaks. In addition, overall variation among all genotypes observed remains low. Thus, our data indicate that EBOV is not undergoing rapid evolution in humans during the current outbreak. This finding has important implications for outbreak response and public health decisions and should alleviate several previously raised concerns.

Both matrix proteins of Ebola virus contribute to the regulation of viral genome replication and transcription

Ebola virus (EBOV) causes severe hemorrhagic fevers in humans and non-human primates. While the role of the EBOV major matrix protein VP40 in morphogenesis is well understood, nothing is known about its contributions to the regulation of viral genome replication and/or transcription. Similarly, while it was reported that the minor matrix protein VP24 impairs viral genome replication, it remains unclear whether it also regulates transcription, since all common experimental systems measure the combined products of replication and transcription. We have developed systems that allow the independent monitoring of viral transcription and replication, based on qRT-PCR and a replication-deficient minigenome. Using these systems we show that VP24 regulates not only viral genome replication, but also transcription. Further, we show for the first time that VP40 is also involved in regulating these processes. These functions are conserved among EBOV species and, in the case of VP40, independent of its budding or RNA-binding functions.

The Ebola virus ribonucleoprotein complex: a novel VP30-L interaction identified

The ribonucleoprotein (RNP) complex of Ebola virus (EBOV) is known to be a multiprotein/RNA structure, however, knowledge is rather limited regarding the actual protein-protein interactions involved in its formation. Here we show that singularly expressed VP35 and VP30 are present throughout the cytoplasm, while NP forms prominent cytoplasmic inclusions and L forms smaller perinuclear inclusions. We could demonstrate the existence of NP-VP35, NP-VP30 and VP35-L interactions, similar to those described for Marburg virus (MARV) based on the redistribution of protein partners into NP and L inclusion bodies. Significantly, a novel VP30-L interaction was also identified and found to form as part of an NP-VP30-L bridge structure, similar to that formed by VP35. The identification of these interactions allows a preliminary model of the EBOV RNP complex structure to be proposed, and may provide insight into filovirus transcriptional regulation.

A system for functional analysis of Ebola virus glycoprotein

Ebola virus causes hemorrhagic fever in humans and nonhuman primates, resulting in mortality rates of up to 90%. Studies of this virus have been hampered by its extraordinary pathogenicity, which requires biosafety level 4 containment. To circumvent this problem, we developed a novel complementation system for functional analysis of Ebola virus glycoproteins. It relies on a recombinant vesicular stomatitis virus (VSV) that contains the green fluorescent protein gene instead of the receptor-binding G protein gene (VSVDeltaG*). Herein we show that Ebola Reston virus glycoprotein (ResGP) is efficiently incorporated into VSV particles. This recombinant VSV with integrated ResGP (VSVDeltaG*-ResGP) infected primate cells more efficiently than any of the other mammalian or avian cells examined, in a manner consistent with the host range tropism of Ebola virus, whereas VSVDeltaG* complemented with VSV G protein (VSVDeltaG*-G) efficiently infected the majority of the cells tested. We also tested the utility of this system for investigating the cellular receptors for Ebola virus. Chemical modification of cells to alter their surface proteins markedly reduced their susceptibility to VSVDeltaG*-ResGP but not to VSVDeltaG*-G. These findings suggest that cell surface glycoproteins with N-linked oligosaccharide chains contribute to the entry of Ebola viruses, presumably acting as a specific receptor and/or cofactor for virus entry. Thus, our VSV system should be useful for investigating the functions of glycoproteins from highly pathogenic viruses or those incapable of being cultured in vitro.