Filovirus Structural Biology: The Molecules in the Machine

Abstract

In this chapter, we describe what is known thus far about the structures and functions of the handful of proteins encoded by filovirus genomes. Amongst the fascinating findings of the last decade is the plurality of functions and structures that these polypeptides can adopt. Many of the encoded proteins can play multiple, distinct roles in the virus life cycle, although the mechanisms by which these functions are determined and controlled remain mostly veiled. Further, some filovirus proteins are multistructural: adopting different oligomeric assemblies and sometimes, different tertiary structures to achieve their separate, and equally essential functions. Structures, and the functions they dictate, are described for components of the nucleocapsid, the matrix, and the surface and secreted glycoproteins.

Ebola virus inclusion body formation and RNA synthesis are controlled by a novel domain of NP interacting with VP35

“…These data clearly suggest that NP-Ct has an important role in genomic RNA incorporation or stability within the VLP nucleocapsids, and as such defines a novel function for this domain. Our finding that NP(1-641) has wild-type transcription/replication activity in p0 cells is consistent with it containing previously identified binding sites for VP35 and VP30 that support transcription/replication, as well as the novel binding site for VP35 described in this work (the CD), in addition to its other well-characterized N-terminal domain functions (aa 1-450) (29, 31, 32).…”

“…IBs within EBOV infected cells are initially small and located near the endoplasmic reticulum, but become more widespread as infection progresses, and many increase in size (17, 29, 30). They contain viral proteins NP, VP35, VP40, VP30, VP24 and L, which are involved in various aspects of positive and negative sense RNA synthesis, nucleocapsid assembly and function, and viral maturation (30-32). Indeed, intact viral nucleocapsids have been visualized within EBOV IBs (18, 29, 33).…”

“…In contrast, other viral nucleocapsid proteins fail to exhibit this behavior when individually expressed (34, 35, 38, 39), although there are somewhat conflicting data regarding the L polymerase in this regard. NP is a multifunctional 739 aa protein that is the most abundant component of the viral nucleocapsid, and in addition to triggering IB formation, its roles include RNA packaging, acting as a co-factor for RNA synthesis carried out by the viral polymerase L, and nucleocapsid assembly (32). A second viral protein, VP35, is also a required co-factor for EBOV and MARV RNA synthesis and is important in nucleocapsid function and assembly (40, 41).…”

Species-Specific Functional Regions of the Green Alga Gamete Fusion Protein HAP2 Revealed by Structural Studies

“…In C. reinhardtii HAP2, the longest is loop E 0 F 0 (residues 239–284), a 45-residue-long segment rich in proline and serine/threonine residues (Figure S2A), which are typical of heavily O-glycosylated proteins such as the mucins (Shogren et al., 1989) (Figure 2A, left panel, and Figure S2A). Mucin-like regions (MLRs), which are known to confer unique rheological properties on proteins (Tabak, 1995), are present on viral proteins involved in attachment to cells, for instance in glycoprotein C of herpes simplex viruses (Rajcani and Vojvodova, 1998), the respiratory syncytial virus glycoprotein G (Satake et al., 1985, Wertz et al., 1985), or in the surface glycoprotein of Ebola virus (Kirchdoerfer et al., 2017). These viral proteins have in common the recognition and binding of glycosaminoglycans (GAGs) present at the surface of target cells, and the MLR was shown to modulate GAG binding (Altgarde et al., 2015).…”

Protein Interaction Mapping Identifies RBBP6 as a Negative Regulator of Ebola Virus Replication

“…The EBOV genome is approximately 19 kilobases in length and encodes at least 9 translation products from 7 separate transcriptional units (Feldmann et al, 2015; Messaoudi et al, 2015). These genes encode the viral nucleoprotein (NP), viral protein of 35 kDa (VP35), VP40, a secreted glycoprotein (sGP), a type I transmembrane glycoprotein (GP), a second secreted glycoprotein (ssGP), VP30, VP24, and the large protein (L), which is the viral polymerase (Kirchdoerfer et al, 2017). NP associates with the viral genomic and antigenomic RNAs throughout the course of infection and is required for viral mRNA synthesis (transcription) and viral genome RNA replication (Muhlberger, 2007; Su et al, 2018).…”