Capture and imaging of a prehairpin fusion intermediate of the paramyxovirus PIV5

Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 12/2011; 108(52):20992-7. DOI: 10.1073/pnas.1116034108
Source: PubMed


During cell entry, enveloped viruses fuse their viral membrane with a cellular membrane in a process driven by energetically favorable, large-scale conformational rearrangements of their fusion proteins. Structures of the pre- and postfusion states of the fusion proteins including paramyxovirus PIV5 F and influenza virus hemagglutinin suggest that this occurs via two intermediates. Following formation of an initial complex, the proteins structurally elongate, driving a hydrophobic N-terminal "fusion peptide" away from the protein surface into the target membrane. Paradoxically, this first conformation change moves the viral and cellular bilayers further apart. Next, the fusion proteins form a hairpin that drives the two membranes into close opposition. While the pre- and postfusion hairpin forms have been characterized crystallographically, the transiently extended prehairpin intermediate has not been visualized. To provide evidence for this extended intermediate we measured the interbilayer spacing of a paramyxovirus trapped in the process of fusing with solid-supported bilayers. A gold-labeled peptide that binds the prehairpin intermediate was used to stabilize and specifically image F-proteins in the prehairpin intermediate. The interbilayer spacing is precisely that predicted from a computational model of the prehairpin, providing strong evidence for its structure and functional role. Moreover, the F-proteins in the prehairpin conformation preferentially localize to a patch between the target and viral membranes, consistent with the fact that the formation of the prehairpin is triggered by local contacts between F- and neighboring viral receptor-binding proteins (HN) only when HN binds lipids in its target membrane.

    • "In this study, it was found that the 'strap' peptide was the first region of F to be released (Poor et al., 2014). Once F is triggered, successful membrane merger requires that the target membrane must be within the range of insertion of the fusion peptide, estimated at a distance of 210 Å (Kim et al., 2011). The viral membrane attachment proteins HN, H or G, bound to receptors on the host membrane presumably brings cellular and viral membranes within this range such that productive insertion of the F fusion peptide into the target membrane can occur to initiate the fusion process. "
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    ABSTRACT: The Paramyxoviridae include some of the great and ubiquitous disease-causing viruses of humans and animals. In most paramyxoviruses, two viral membrane glycoproteins, fusion protein (F) and receptor binding protein (HN, H or G) mediate a concerted process of recognition of host cell surface molecules followed by fusion of viral and cellular membranes, resulting in viral nucleocapsid entry into the cytoplasm. The interactions between the F and HN, H or G viral glycoproteins and host molecules are critical in determining host range, virulence and spread of these viruses. Recently, atomic structures, together with biochemical and biophysical studies, have provided major insights into how these two viral glycoproteins successfully interact with host receptors on cellular membranes and initiate the membrane fusion process to gain entry into cells. These studies highlight the conserved core mechanisms of paramyxovirus entry that provide the fundamental basis for rational anti-viral drug design and vaccine development. Copyright © 2015 Elsevier Inc. All rights reserved.
    No preview · Article · Mar 2015 · Virology
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    • "Since E2 does not contain any clearly recognizable fusion motifs to insert into the host cell membrane, E1 is thought to bear the fusion motif in pestiviruses (El Omari et al., 2013; Li et al., 2013). If so, E1 would have to at least transiently extend to span the distance between the cellular and viral membranes prior to membrane fusion, approximately 20 nm (Kim et al., 2011). With only 177 amino acids in its ectodomain, or 143 amino acids excluding the predicted perimembrane helices, E1 would have to adopt a highly elongated fold in order to span 20 nm. "
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    ABSTRACT: The membrane anchors of viral envelope proteins play essential roles in cell entry. Recent crystal structures of the ectodomain of envelope protein E2 from a pestivirus suggest that E2 belongs to a novel structural class of membrane fusion machinery. Based on geometric constraints from the E2 structures, we generated atomic models of the E1 and E2 membrane anchors using computational approaches. The E1 anchor contains two amphipathic perimembrane helices and one transmembrane helix; the E2 anchor contains a short helical hairpin stabilized in the membrane by an arginine residue, similar to flaviviruses. A pair of histidine residues in the E2 ectodomain may participate in pH sensing. The proposed atomic models point to Cys987 in E2 as the site of disulfide bond linkage with E1 to form E1-E2 heterodimers. The membrane anchor models provide structural constraints for the disulfide bonding pattern and overall backbone conformation of the E1 ectodomain.
    Full-text · Article · Apr 2014 · Virology
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    • "However, evidence of the extended intermediate has been largely indirect (Jiang et al., 1993; Miller et al., 2011; Pessi et al., 2012). Two recent reports have provided direct information about the extended intermediates in paramyxoviruses (Kim et al., 2011) and avian sarcoma leukosis virus (ASLV) (Cardone et al., 2012; Matsuyama et al., 2004). At present, no extended intermediate conformation from any virus has been characterized in high resolution. "
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    ABSTRACT: Viral fusion proteins undergo dramatic conformational transitions during membrane fusion. For viruses that enter through the endosome, these conformational rearrangements are typically pH sensitive. Here, we provide a comprehensive review of the molecular interactions that govern pH-dependent rearrangements and introduce a paradigm for electrostatic residue pairings that regulate progress through the viral fusion coordinate. Analysis of structural data demonstrates a significant role for side-chain protonation in triggering conformational change. To characterize this behavior, we identify two distinct residue pairings, which we define as Histidine-Cation (HisCat) and Anion-Anion (AniAni) interactions. These side-chain pairings destabilize a particular conformation via electrostatic repulsion through side-chain protonation. Furthermore, two energetic control mechanisms, thermodynamic and kinetic, regulate these structural transitions. This review expands on the current literature by identification of these residue clusters, discussion of data demonstrating their function, and speculation of how these residue pairings contribute to the energetic controls.
    Full-text · Article · Jul 2013 · Structure
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