A Filovirus-Unique Region of Ebola Virus Nucleoprotein Confers Aberrant Migration and Mediates Its Incorporation into Virions

Abstract

The Ebola virus nucleoprotein (NP) is an essential component of the nucleocapsid, required for filovirus particle formation and replication. Together with virion protein 35 (VP35) and VP24, this gene product gives rise to the filamentous nucleocapsid within transfected cells. Ebola virus NP migrates aberrantly, with an apparent molecular mass of 115 kDa, although it is predicted to encode an ϳ85-kDa protein. In this report, we show that two domains of this protein determine this aberrant migration and that this region mediates its incorporation into virions. These regions, amino acids 439 to 492 and amino acids 589 to 739, alter the mobility of Ebola virus NP by sodium dodecyl sulfate-polyacrylamide gel electrophoresis by 5 and 15 kDa, respectively, and confer similar effects on a heterologous protein, LacZ, in a position-independent fashion. Furthermore, when coexpressed with VP40, VP35, and VP24, this region mediated incorporation of NP into released viruslike particles. When fused to chimeric paramyxovirus NPs derived from measles or respiratory syncytial virus, this domain directed these proteins into the viruslike particle. The COOH-terminal NP domain comprises a conserved highly acidic region of NP with predicted disorder, distinguishing Ebola virus NPs from paramyxovirus NPs. The acidic character of this domain is likely responsible for its aberrant biochemical properties. These findings demonstrate that this region is essential for the assembly of the filamentous nucleocapsids that give rise to filoviruses.Ebola virus is a member of the family Filoviridae, most closely related to the paramyxoviruses among the negativestranded RNA viruses. Filoviruses are characterized by their enveloped, nonsegmented, and filamentous forms, and these viruses replicate rapidly in monocytes/macrophages, fibroblasts, and endothelial cells during acute infection (7,10,24). Ebola virions are characterized by their longitudinal fibers, with forms ϳ970 nm in length displaying optimal infectivity (9). They otherwise show a uniform diameter. In previous studies, three viral proteins-Ebola virus nucleoprotein (NP), virion protein 35 (VP35), and VP24-were shown to be necessary and sufficient for the formation of nucleocapsid-containing viruslike structures in transfected cells (13). Although expression of VP40 gives rise to filamentous vesicles when expressed in cells, it does not by itself allow formation of nucleocapsid-containing viruslike particles (2,11,15,19,26). Transfection of these genes gave rise to nucleocapsids confirmed by transmission electron microscopy, and they appear to be necessary and sufficient for the formation of these particles within cells. In a previous study, NP was found to interact with glycan-binding proteins (lectins) (13), and it was suggested that this posttranslational modification may account for its aberrant migration. A subsequent investigation provided further insight into the structure-function relationship within NP, including the role of the first 450 amino acids in NP-NP interactions and vi...

Ebola Virus Does Not Induce Stress Granule Formation during Infection and Sequesters Stress Granule Proteins within Viral Inclusions

“…In line with previous reports, our data show that VP35 is also able to disrupt NP-mediated inclusion formation when expressed at large amounts (68). Similar to the SG nucleating proteins, NP is the assembly factor of RNA-protein aggregates, the viral inclusions, and serves as a hub for the recruitment of other viral proteins, including VP35 (6,76). The disruption in inclusion formation by VP35 might be related to a recently identified intrinsically disordered region within VP35, which mediates binding to monomeric NP and interferes with NP self-aggregation (77,78).…”

Cold Adaptation, Ca2+ Dependency and Autolytic Stability Are Related Features in a Highly Active Cold-Adapted Trypsin Resistant to Autoproteolysis Engineered for Biotechnological Applications

“…The first corresponds to the molecular mass of MBP and the second is the active KT1, which was confirmed by Western blot (Figure 6). KT1 presents an anomalous migration in SDS-PAGE, consistent with our previous results [30], which can be explained by its high content of acidic amino acids and very low pI [57–60]. Two other relevant bands around 26 and 17 kDa also appeared after enterokinase digestion (Figure 5A).…”

Electron Cryo-microscopy Structure of Ebola Virus Nucleoprotein Reveals a Mechanism for Nucleocapsid-like Assembly

“…We and others have previously identified a region at the N-terminus of eNP that is conserved among paramyxoviruses and filoviruses, spanning residues 1–450, whereas the C-terminal portion of eNP encompassing residues 451–739 is unique to filoviruses (Leung et al, 2015; Shi et al, 2008; Watanabe et al, 2006) (Figure 1A). Using a combination of biophysical analysis and X-ray crystallographic studies, we determined a structured region in the eNP N-terminus using a truncated N-terminal domain construct (PDB 4YPI)(Leung et al, 2015).…”